Advances in Child Development and Behavior Volume 5

ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR

VOLUME 5

Contributors to This Volume John H . Flavell Kathryn S. Goodwin L. R. Goulet

Frances K. Graham Tryphena Humphrey Corinne Hutt Jan C. Jackson

ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR edited by Hayne W. Reese Department of Human Development University of Kansas Lawrence, Kansas

Lewis P. Lipsitt Department of Psychology Brown University Providence, Rhode Island

VOLUME 5

@ 1970 ACADEMIC PRESS

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London

COPYRIGHT @ 1970,

BY

ACADEMICPRESS,INC.

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U n i t d Kingdom Edition published by ACADEMIC PRESS. I N C . ( L O N D O N ) LTD. Berkeley Square Houre. London W I X 6BA

LIBRARY OF

CONGRESS CATALOG C A R D

NUMBER: 63-23237

P R I N T E D IN T H E U N I T E D S T A T E S OF A M E R I C A

Contents LISTOF CONTRIBUTORS ....................................................

PREFACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTENTSOF PREVIOUS VOLUMES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

vii ix

xi

The Development of Human Fetal Activity and Its Relation to Postnatal Behavior TRYPHENA HUMPHREY

. ...... .......... .................. 2 Historical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theories on the Development of Behavior ................. 4 ............ Methods of Investigating Behavioral Devel Activity in Response to Tactile Stimulation of Human Fetuses Fetal Activity in Response to Other Types of Stimuli . . . . . . . . . . Spontaneous Activity . . . ............................ VIII. The Relation of lntegratio the Development of Behavior . IX. Other Considerations ............................................... 49 References . . ........................... 51 I. Introduction

11. 111. IV. V. VI. VII.

Arousal Systems and lnfant Heart Rate Responses FRANCES K. GRAHAM A N D JAN C. JACKSON

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

........................................................ 111. Developmental Studies of Evoked HR Response . . . . . . . . . . . . . . . . . . . . . . . I V . Summary and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II. Procedure

60 67 78 108 1II

Specific and Diversive Exploration CORINNE HUTT I. Introduction . . . . . 11. Complexity as a De 111. Novelty as a Determinant of Exploration IV. Specific and Diversi V . Summary and Conclusions . . . . References . . . . . . . . . . . . . . . .

..........

120

V

vi

Contents

Developmental Studies of Mediated Memory JOHN H . FLAVELL

I . Introduction ....................................................... I 1 . The Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1 . Some Impressions Regarding the Nature and Development of Mediated Memory ................................................. IV . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

182 182 193 208 209

Development and Choice Behavior in Probabilistic and Problem-Solving Tasks L. R . GOULET A N D KATHRYN S . GOODWIN

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I I . Probability Learning ................................................ 1 1 1 . OtherTasks ...................................................... IV . Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

214 214 241 249 250

INDEX AUTHOR

.........................................................

255

INDEX SUBJECT

..........................................................

263

List of Contributors Numbers in parentheses indicate the pages on which the authors' contributions begin.

JOHN H . FLAVELL, University of Minnesota, Minneapolis, Minnesota (181)

KATHRYN S. GOODWIN, West Virginia University, Morgantown, Virginia ( 2 1 3 )

L. R. GOULET,' West Virginia University, Morgantown, Virginia ( 2 1 3 )

FRANCES K. GRAHAM, University of Wisconsin, Madison, Wisconsin ( 5 9 )

TRYPHENA HUMPHREY, Department of Anatomy, Medical Center, University of Alabama in Birmingham, Birmingham, Alabamu ( 1 )

CORINNE HUTT,* Human Research U n i t , University of Oxford, Oxford, England ( 1 19)

JAN C. JACKSON, University of Wisconsin, Madison, Wisconsin ( 5 9 )

'Present address: University of Illinois, Urbana, Illinois. 2Present address: Department of Psychology, University of Reading, Reading. England. vii

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Preface The amount of research and theoretical discussion in the field of child development and behavior is so vast that researchers, teachers, and students are confronted with a formidable task in keeping abreast of new developments within their areas of specialization through the use of primary sources, not to mention remaining knowledgeable in areas peripheral to their primary focus of interest. Moreover, there is often simply not enough journal space to permit publication of more speculative kinds of analyses which might spark expanded interest in a problem area or stimulate new modes of attack on the problem. The serial publication of Advances in Child Development and Behavior is intended to ease the burden by providing scholarly technical articles serving as reference material and by providing a place for publication of scholarly speculation. In these documented, critical reviews, recent advances in the field are summarized and integrated, complexities are exposed, and fresh viewpoints are offered. They should be useful not only to the expert in the area but also to the general reader. The publication of Volume 5 marks a change from a biennial to an annual rate, made desirable by the unabated increase in the number of primary sources being published and by an increase in the rate at which new advances seem to be made. No attempt is made to organize each volume around a particular theme or topic, nor is the series intended to reflect the development of new fads. Manuscripts are solicited from investigators conducting programmatic work on problems of current and significant interest. The editors often encourage the preparation of critical syntheses dealing intensively with topics of relatively narrow scope but of considerable potential interest to the scientific community. Contributors are encouraged to criticize, integrate, and stimulate, but always within a framework of high scholarship. Although appearance in the volumes is ordinarily by invitation, unsolicited manuscripts will be accepted for review if submitted first in outline form to the senior editor. With the publication of Volume 5 of this ix

X

Preface

series, Lewis P. Lipsitt will have phased out as coeditor and Hayne W. Reese will be the sole editor of Advances in Child Development and Behavior. We wish to acknowledge with gratitude the aid of our home institutions, the University of Kansas and Brown University, which generously provided time and facilities to produce this volume.

HAYNEW. REESE August, 1970

LEWISP. LIPSITT

CONTENTS OF PREVIOUS VOLUMES Volume 1 Responses of Infants and Children to Complex and Novel Stimulation Gordon N . Cantor Word Associations and Children’s Verbal Behavior David S . Palermo Change in the Stature and Body Weight of North American Boys during the Last 80 Years Howard V . Meredith Discrimination Learning Set in Children Hayne W . Reese Learning in the First Year of Life Lewis P . Lipsitt Some Methodological Contributions from a Functional Analysis of Child Development Sidney W . Bijou and Donald M . Baer The Hypothesis of Stimulus Interaction and an Explanation of Stimulus Compounding Charles C . Spiker The Development of “Overconstancy” in Space Perception Joachim F . Wohlwill Miniature Experiments in the Discrimination Learning of Retardates Betty J . House and David Zeaman AUTHOR INDEX -SUBJECT

INDEX

Volume 2 The Paired-Associates Method in the Study of Conflict Alfred Castaneda Transfer of Stimulus Pretraining in Motor Paired-Associate and Discrimination Learning Tasks Joan H . Cantor xi

xii

Contents of Previous Volumes

The Role of the Distance Receptors in the Development of Social Responsiveness Richard H . Walters and Ross D . Parke Social Reinforcement of Children’s Behavior Harold W . Stevenson Delayed Reinforcement Effects Glenn Terrell A Developmental Approach to Learning and Cognition Eugene S . Gollin Evidence for a Hierarchical Arrangement of Learning Processes Sheldon H . White Selected Anatomic Variables Analyzed for Interage Relationships of the Size-Size, Size-Gain, and Gain-Gain Varieties Howard V . Meredith AUTHOR INDEX-SUBJECT

INDEX

Volume 3 Infant Sucking Behavior and Its Modification Herbert Kaye The Study of Brain Electrical Activity in Infants Robert J . Ellingson Selective Auditory Attention in Children Eleanor E. Maccoby Stimulus Definition and Choice Michael D . Zeiler Experimental Analysis of lnferential Behavior in Children Tracy S . Kendler and Howard H . Kendler Perceptual Integration in Children Herbert L. Pick, Jr., Anne D . Pick, and Robert E. Klein Component Process Latencies in Reaction Times of Children and Adults Raymond H . Hohle AUTHOR INDEX-SUBJECT

INDEX

Volume 4 Developmental Studies of Figurative Perception David Elkin d

Contents of Previous Volumes

xiii

The Relations of Short-Term Memory to Development and Intelligence John M . Belmont and Earl C . Butterfield Learning, Developmental Research, and Individual Differences Frances Degen Horowitz Psychophysiological Studies in Newborn Infants S . J . H u t t , H . C . Lenard, and H . F . R . Prechtl Development of the Sensory Analyzers during Infancy Yvonne Brackbill and Hiram E . Fitzgerald The Problem of Imitation Justin Aronfreed AUTHOR INDEX -SUBJECT

INDEX

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THE DEVELOPMENT OF HUMAN FETAL ACTIVITY AND ITS RELATION TO POSTNATAL

Tryphena Humphrey UNIVERSITY OF ALABAMA IN BIRMINGHAM

1. 11.

INTRODUCTION

............................................

HISTORICAL B A C K G R O U N D

................................

111. T H E O R I E S O N T H E D E V E L O P M E N T OF BEHAVIOR

.........

A. T O T A L PATTERN C O N C E P T O F C O G H I L L A N D O T H E R S B. LOCAL REFLEX C O N C E P T OF W I N D L E . . . . . . . . . . . . . . . . . C. O T H E R VIEWS O N BEHAVIORAL DEVELOPMENT . . . . . . . IV.

M E T H O D S OF INVESTIGATING BEHAVIORAL DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

'This investigation was supported by a U.S. Public Health Service research career program award, NB-K6-167 16, from the National Institute of Neurological Diseases and Blindness. *Aided by Grant HD-00230, National lnstitute of Child Health and Human Development, National Institutes of Health. The present paper is publication No. 55 in a series of functional and morphological studies on human prenatal development begun under the direction of Dr. Davenport Hooker in 1932. The cinematographic records and the morphologic material upon which this paper is based were accumulated under the support of previous grants from the Penrose Fund of the American Philosophical Society, the Carnegie Corporation of New York, the University of Pittsburgh, the Sarah Mellon Scaife Foundation of Pittsburgh, and Grant 8-394 from the National Institute of Neurological Diseases and Blindness, National Institutes of Health. I

2

Tryphena Humphrey

A. METHODS O F RECORDING ACTIVITY . . . . . . . . . . . . . . . . . . B. TYPES OF STIMULI USED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. EFFECTS O F ANOXIA, ASPHYXIA, ANESTHETICS, NARCOTICS. AND OTHER DRUGS . . . . . . . . . . . . . . . . . . . . . . V. ACTIVITY I N RESPONSE TO TACTILE STIMULATION OF HUMAN FETUSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. T H E PERIOD O F WIDESPREAD REACTIONS-COGHILL’S TOTAL PATTERN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. THE DEVELOPMENI- OF LOCALIZED REFLEX ACTIVITY C. FUNCTION O F FETAL REFLEXES . . . . . . . . . . . . . . . . . . . . . . . D. T H E RELATION O F SUPPRESSION (OR INHIBITION) OF ACTIVITY T O T H E DEVELOPMENT O F BEHAVIOR . . . . . E. POSTNATAL REPETITION OF FETAL REFLEX ACTIVITY SEQUENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI. FETAL ACTIVITY IN RESPONSE T O OTHER TYPES O F STIMULI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII. SPONTANEOUS ACTIVITY . . . . . . . . . . . . . . . . . . . .

8 9 10

12 12 16

30 36

40

41

43

VIII. T H E RELATION O F INTEGRATION T O T H E DEVELOPMENT O F BEHAVIOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46

IX. OTHER CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51

I.

Introduction

Prior to the meticulous investigations of Coghill that correlated functional changes with the development of the nervous system in Amblysroma ( 1909- 1930), most of the observations on the development of vertebrate behavior were limited in scope. Coghill’s correlations of structure and function and his theory on the development of behavior mark the onset of the organized attempts to correlate the sequence of behavioral development, as demonstrated by the progressive changes in reflex and spontaneous activity, with the development of the nervous system. Differences in views on the mode of behavioral development arose, as differences do in connection with any significant new concept. Adequate evidence to support the theories that were advanced was not forthcoming and the interest in such behavioral investigations declined. In some recent review papers particularly, the value of Coghill’s investi-

The Development of Human Fetal Activity

3

gations of behavioral development has been minimized or even casually dismissed as of no significance in determining either the mechanisms or the causal factors of behavior (e.g., Jacobson, 1966). Indeed, the brief and none too accurate references lead one to speculate, in some cases, concerning the degree of familiarity of the authors with these concepts. Following the advances in experimental neuroembryology, in neurophysiology, in the relation of genetic factors to the development of the nervous system, in the ultramicroscopic structure of neurons and synapses, in histochemistry of the nervous system, and in endocrine interrelations, attention has turned to the relationship of data from such fields to behavior, with little or no attempt at correlation with the sequential changes in activity, or overt behavior, as development progresses. However significant the data from any specialized field may prove to be, they can contribute only in an ancillary capacity to our knowledge and understanding of the manner in which behavior develops. Discovery of the causes and mechanisms involved in behavior will depend upon acquiring a more complete knowledge of the developmental sequence of the reactions of the fetus to its total environment, upon correlating this knowl-. edge with the morphologic development of the nervous system, with the relevant knowledge from neurophysiology, and with the part played by genetics and prenatal function, when their roles are better understood than at present. Neither the mechanisms nor the causes of behavior can be determined when prenatal activity, which constitutes the “taproot of behavior [Gottlieb, 19641,” is ignored.

11. Historical Background Because we are concerned here with the development of human fetal behavior, a routine review of the behavioral literature related to other vertebrates would contribute little value. Therefore, only the references that are relevant to the points considered will be included. The reviews of Carmichael (1934, 1954), of Coghill ( 1 940), of Hamburger (1 963, 1964), of Hooker (1942, 1944, 1952), and of Windle and his collaborators ( 193 1- 1950) cover these fields. For the observations on human fetal behavior, however, a short resume of the various investigations is appropriate. Some mention of human fetal movements was made in the nineteenth century, even as early as 1837 (Erkbam), but the systematic collection of data began in 1920 with the well-organized investigations of the psychiatrist, Minkowski. The isolated observations made earlier by Strassman ( 1903) and by Yanase ( 1 907) will be considered later (Section

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Tryphena Humphrey

IX). Although the data of Minkowski (1928) were based on “75 or more fetuses [Hooker, 19521,” including both normal fetuses and those having transection of the central nervous system at different levels, no fetuses under 40 mm in crown-heel length were examined. Consequently, the earliest developing reflexes were not seen. All of his conclusions were based on observations dictated when the reflexes were elicited. For fetal reflexes that include action in several areas, the rapid speed of execution makes complete analysis of the movements virtually impossible. Therefore, the accuracy of the reports of Minkowski is truly remarkable. Other investigations of human fetal reflexes during this period were made by Bolaffio and Artom ( 1 924), who reported on about 28 fetuses, but without the maintenance of as satisfactory environmental conditions or methods of stimulation as used by Minkowski. Somewhat later several human fetuses were tested with a variety of stimuli by Windle and his collaborators [Fitzgerald & Windle, 1942, 15 fetuses, 18.0 to 26.0 mm crown-rump measurement (CR); Windle & Becker, 1940, 3 fetuses, 34-40 mm CR length]. Only four of the small fetuses (20.0-26.0 mm) were motile, but “Continuous motion picture records of the experiments performed at the operating table were made [Fitzgerald & Windle, 1942, p. 1601.” Unfortunately, the pictorial records were not published. Reports on human fetal reflexes have appeared during recent years from the USSR (Golubewa, Shulejkina, & Vainstein, 1959; Mavrinskaya, 1960). Most of the data are from observations on older fetuses and premature infants. It has not been possible either to determine satisfactorily the total number of cases studied or to correlate activity with fetal age in many instances. The present account of human fetal activity is based almost entirely on the observations begun in 1932 by Davenport Hooker at the University of Pittsburgh. From 1938 to 1963 the author was associated closely with this program. The investigations on fetal activity include premotile embryos and a total of 136 motile fetuses and premature infants. Motion picture records are available for the majority of these cases and dictated records for the others. It is on the analysis of these motion picture records, however, both by Hooker and by the author, that the interpretations presented in this paper are based.

111. Theories on the Development of Behavior Most theories tend to emphasize one major aspect of a problem without equal consideration of other points. After one theory is set forth, an opposing one is proposed, supporters for both appear, and variations

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5

and modifications of the theories arise. The theories, or parts of them, may be applied in related fields, with beneficial or adverse effects. Without additional evidence, however, interest diminishes, only to reappear later, when new evidence is found. Such is the history of the investigations on the development of human behavior. The revival of interest and the relation of prenatal activity to the development of postnatal behavior make it especially appropriate to review the major theories at the present time. A. TOTALPATTERN CONCEPT OF COGHILL AND OTHERS

From his observations on tailed amphibians, Coghill ( 1929) found that reflex activity in response to touch began in the cervical region and spread caudalward throughout the trunk to include the tail, as development progressed. At first the extremities were moved passively by the change in the position of the trunk. Consequently, the forelimbs were moved earlier than the hindlimbs. Later, when the extremities moved independently, the action appeared in a proximodistal sequence. From these observations Coghill (1929, p. 38) concluded that “Behavior develops from the beginning through the progressive expansion of a perfectly integrated total pattern and the individuation within it of partial patterns which acquire various degrees of discreteness.” Coghill found that gill movements, like limb activity, occurred with head and trunk movements before appearing alone. Similarly, jaw movements began in association with a forward jump involving both trunk and extremities. After making extensive correlations with the observations of Minkowski (1928) on human fetal activity, and with the development of behavior in other higher vertebrates, Coghill ( 1 940) concluded that mammalian behavior followed the same general sequence in development. Whereas Coghill stressed the basic pattern underlying development throughout vertebrate phylogeny and emphasized the involvement of the total organism in the development of overt behavior, others attached more significance to the differences between behavioral development in Amblystoma and that in other vertebrates, particularly mammals. Because the first reflexes to appear were usually limited to the neck region (or the neck and upper extremities) they were interpreted as local reflexes (Windle, 1950; Windle & Becker, 1940) rather than the initial stage in the development of a total body response which is limited in its extent because only the cervical region of the neuromuscular system has attained a functional level of development. In his recent investigation on the development of activity in macaque fetuses, Bodian ( 1 968) also made this interpretation.

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Tryphena Humphrey

Coghill related the primitive sensory and motor systems in Amblystoma with the early total pattern phase of behavior, and the permanent motor neurons and sensory ganglia with the appearance of independent limb reflexes. Although it was later shown that some nerve cells comparable to the primitive neurons of lower vertebrates may appear briefly and degenerate in human embryos (Humphrey, 1944, 1950), the supposed lack of a primitive neuronal system in mammals led certain investigators (Ranson, 1943; Windle, 1934) to deny that mammalian behavior could include a total body reaction comparable to Coghill’s total pattern. From his observations on rat fetuses, however, Angulo y Gonzalez ( 1932) concluded that mammalian behavior developed in the general sequence demonstrated by Coghill. The observations of Coronios ( 1933) on cat fetuses support the concept of Coghill to a considerable degree, although those of Windle and his associates on the cat and rat do not (Windle, 1934; Windle & Griffin, 193 I ; Windle, Minear, Austin, & Orr, 1935; Windle, Orr & Minear, 1934). Carmichael (1934, 1954) did not agree with Coghill’s concept in all respects, but the behavioral sequence that he demonstrated for guinea pig fetuses has a surprisingly close relationship. For the sheep, Barcroft and Barron (1939) found localized (or segmental) reflex activity relatively early in development, but concluded that local reflexes “do appear to become segregated out from the total responses in the sense implied by Coghill.” B. LOCALREFLEXCONCEPTOF WINDLE

In the early papers of Windle and his associates (Windle, 1931; Windle & Griffin, 1931; Windle, O’Donnell, & Glasshagle, 1933), behavioral development in the cat was reported to follow the pattern shown by Coghill. After Swenson (1928, 1929) described the simple local limb reflex of rat fetuses secured by lifting a limb and releasing it, Windle .nd his collaborators made similar observations on other mammals SL :h as the cat, (Windle, 1934; Windle & Griffin, 193 1; Windle et al., 193 4) as well as on the rat (Windle et a f . , 1935). From these investigations and from their observations on the behavior of chick embryos (Orr & Windle, 1934; Windle & Orr, 1934), Windle and his associates concluded that in the higher vertebrates simple, local reflexes constitute the units of behavior which are combined and integrated secondarily to build up coordinated behavioral patterns. Because the observations on human fetuses were not made with the placental circulation intact, but while the fetal oxygen supply was diminishing and carbon dioxide and other metabolites accumulating, Windle considered total pattern reflexes to be abnormal mass movements and not the beginning stage in normal behavioral development.

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C. OTHERVIEWSON BEHAVIORALDEVELOPMENT

Other theories on the development of behavior that deserve special mention are those of Kuo and of Hamburger, who studied the development of behavior in birds, and of the Soviet investigators who worked with human fetuses. In his book on the development of behavior, Kuo (1967, p. 92) emphasized that for any given response and in any given stage of development, the entire organism is involved, either actively or passively. Kuo introduced the concepts of “behavioral gradients” and “behavioral potentials” and stressed that visceral activity and biophysical and biochemical changes are essential parts of the responses of an animal. As the resuIt of their investigations on the development of activity in the chick, Hamburger and his collaborators (Hamburger, 1963; Hamburger, Balaban, Oppenheim, & Wenger, 1965) recognized two components in the development of behavior that “can be dissociated from each other [Hamburger, 1963, p. 35 I]”- spontaneous activity and reflexogenic motility. Furthermore, Hamburger postulated that spontaneous activity is the primary type of behavior and that reflexogenic activity is secondary to it (see Section VII). Spontaneous activity is not integrated and consists of periodic (or cyclic), rhythmic movements resulting from the “self-generated automatic discharge of neurons [Hamburger, I963 p. 3511.” Spontaneous activity was recognized by Weiss in 1955 as uncoordinated. The activity is not random, however, and the marked periodicity is not altered by sensory input (Hamburger, Wenger, & Oppenheim, 1966). The views of the Soviet workers are based mainly on their observations on human fetuses, but data on the earliest stages in the development of reflex activity are lacking. Their theory of behavioral development stresses heterochronic maturation of the different organs of a system and systemogenesis during behavioral development, that is, selective maturation to create the functional systems which must be mature enough at the time of birth for survival (Anokhin, 1964; Golubewa et al., 1959).

IV. Methods of Investigating Behavioral Development Because the following account is concerned particularly with the development of human fetal behavior, the methods discussed are those related to mammalian investigations. Studies of subhuman mammalian fetal activity can be made with the fetus in situ, but, although tried by Fitzgerald and Windle (1942), this procedure has not been used by

8

Tryphena Humphrey

others for human fetuses. Instead, either the fetus and placenta are removed together at Cesarean section or the umbilical cord is cut. Consequently, the fetal oxygen supply is soon diminished and metabolites accumulate. Anesthetics and drugs given the mother also affect the fetus. In other mammalian investigations, the placental circulation can be maintained for some time and the effects of anoxia and of maternal drugs and anesthetics can be avoided. In addition, the activity can be observed for a longer time, both within the amniotic sac and after removal. Therefore, both reflexogenic and spontaneous movements may be documented repeatedly. Upon removal from the amniotic sac, however, an isotonic fluid bath is essential in order to allow free movement and prevent surface drying. Maintaining the fluid bath at normal body temperature helps to simulate the intrauterine environment. Also the state of relative weightlessness and the lack of gravity effects within the uterus (Reynolds, 1962) are partially reproduced when the fetus is immersed in fluid. A. METHODSOF

RECORDING ACTIVITY

Motion picture recording of fetal activity is unquestionably the most satisfactory and accurate method, for each action may be studied repeatedly. Normal speed (16 frames per second) suffices for the most part, but an exceedingly fast reflex or a rapid part of a complex reaction may be completely missed. Slow motion photography eliminates this handicap, but provides other disadvantages, the major one being the increased cost. Slow motion and normal speed together overcome most of the technical problems. Photographic prints can be made for study andlor publication when color photography is used, but the advantages of color may not be great enough to offset the increased cost. Many of the drawbacks of photography at normal speed may be overcome by studying the films with a motion picture projector that can be slowed, stopped on a single frame, and run by hand so that adjacent frames may be compared repeatedly. Even so, some points may escape detection, may be uncertain, or may be wrongly interpreted without photographic prints. Spaced prints are sufficient if the action is slow, but every frame is needed if the action is quick. By this method each frame showing a reflex can be compared with every other frame. The mouth opening of small fetuses (26.0-28.0 mm CR; Figs. lB, 2B, and 22C) and the position of the tongue in older fetuses (Figs. 7A-B, 8B, 9B, and 19B) are examples. When mouth opening reflexes are first demonstrable, usually only the more extensive, rapidly executed head, trunk and extremity movements are seen, either when the reflex is elicited or later

The Development of Human Fetal Activity

9

when the motion pictures are viewed at normal speed. Likewise, any local activity of older fetuses that either requires less than half a second or is not near the area stimulated is easily missed (Humphrey, 1968a, Figs. 6-7 and 11). By far the greater number of investigations of vertebrate behavior have been based on dictated records alone, although the action was watched by more than one observer. Sometimes magnifying lenses have been used (Windle & Griffin, 1931). Angulo y Gonzalez (1932), Coghill (1929), and Coronios (1933) supplemented their direct observations to a varying degree with motion picture recording. Angulo documented his published account with photographs and Coghill (1929) illustrated the reflexes that he described with drawings from his motion pictures. However, the few reports on the development of reptilian behavior (Lacerta, Hughes, Bryant, & Bellairs, 1967; turtle, Smith & Daniel, 1946; Tuge, 1931) are not based on motion picture recording. In the study of Gottlieb and Kuo (1965) on the prehatching behavior of the Peking duck, motion picture color photography was used, but neither the more recent investigations of Hamburger ( 1 963, 1964) and his associates (Hamburger & Balaban, 1963; Hamburger & Oppenheim, 1967; Hamburger et al., 1966) on avian behavior nor the earlier ones of Windle and his collaborators (Orr & Windle, 1934; Windle & Orr, 1934) employed this technique. Bodian ( 1 968) used cinematographic recording in studying the activity of macaque fetuses, but he did not supplement his published descriptions with photographs. Although Fitzgerald and Windle (1942) recorded the activity of four small human fetuses with motion pictures, no photographs were published. B. TYPESOF STIMULI USED

Reactions to tactile stimuli precede vestibular sensitivity in the chick, according to Gottlieb (1968), and proprioception follows later. Sensitivity to touch develops early for human embryos also. When light touch first constitutes an effective stimulus, all sensory nerve fibers approaching the sensitive surfaces consist of naked, growing nerve tips. Those nearest the epithelium are in the region of the lips (Hogg, 1941; Humphrey, 1966b), but the most superficial cones of growth are still 13-20 p below the basement membrane that separates the epithelium from the underlying tissue when they first become sensitive to light touch. Lightly stroking the cutaneous surfaces with graded hair esthesiometers of known pressure values provides adequate stimulation for eliciting reflexes from human (Hooker, 1942, 1944, 1950, 1952) and other mam-

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Tryphena Humphrey

malian fetuses. Stroking the skin several times is the most effective technique because it produces both spatial and temporal summation; repeated punctate stimuli rarely elicit a reflex. The tips of the stimulators must be covered with an inert, smooth coating to prevent penetration of the epithelium and cause muscle contraction by direct stimulation. If comparisons and correlations are to be made with investigations on other mammals or with other observations on the same one, it is essential to record the type of stimulus and the area stimulated, as well as the reaction elicited. Heavy pressure over a muscle with a probe, for example, or stretch stimuli produced by abducting or extending a limb do not excite the polysynaptic reflex arcs stimulated by light touch but activate the monosynaptic arcs of stretch reflexes. Pressure on the amniotic sac produces effects that are practically impossible either to evaluate or to equate with other types of stimuli. Because the stimuius is transmitted through fluid, it is not only intensified, but also probably transferred to almost all surfaces of the fetus to a varying degree. Therefore stimuli applied to the amniotic sac produce stronger excitatory effects than those of the same strength applied to the fetus directly. Because the fetus is in a confined ovoid space, both lateral flexion and extension of the head and trunk will be more limited in extent than extremity movements. Since they are so inconspicuous, the head and trunk movements may be missed entirely unless photographic prints are compared carefully. Sharp needles or even a stiff hair may cause direct stimulation of the underlying muscle, not reflex action. In the perioral region before the underlying muscle has developed, such strong “mechanical” stimuli will elicit a true reflex distally in the neck and trunk muscles before light touch is effective (Fitzgerald & Windle, 1942). Faradic stimulation of the snout of a small fetus is also effective (sheep, Barcroft & Barron, 1939). Such types of stimuli demonstrate that the polysynaptic arcs are capable of functioning before the epithelial surfaces become sensitive to stimulation. C. EFFECTSOF ANOXIA, ASPHYXIA, ANESTHETICS, NARCOTICS, AND OTHER DRUGS

Almost all investigations on the development of behavior in mammalian fetuses discuss these effects to some extent and extensive accounts are given in the papers of Hooker (1942, 1944, 1952), Humphrey (1 953), and Windle (1944). After placental separation or severance of the umbilical cord, anoxia develops progressively as the oxygen supply is depleted. As carbon dioxide and other metabolites accumulate, asphyxia suppresses all reflex activity.

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When the fetus is first removed from the uterus, most investigators have noted a brief period of quiescence during which reflexes are elicitable with difficulty or not at all (Hooker, 1952; Windle, 1944; Windle & Becker, 1940). These observers and others have suggested that the slight increase in carbon dioxide that soon follows placental separation heightens the excitatory state before asphyxia suppresses activity enti re1y . From their observations on mammalian fetuses, Angulo y Gonzalez (19321, Hooker (1952, 1954) and Windle (1940) all noted that anoxia suppresses the most recently functional reflex arcs first of all, whereas the first arcs to mature remain functional longest. The difference depends on the fact that the more mature reflex arcs require less oxygen to function than do those more recently formed. I t is evident, therefore, that for human fetuses the most newly acquired reflexes can be elicited only at or near the beginning of a period of observation. Consequently the total pattern reflexes remain after asphyxia suppresses other reflex activity. Because the total body reactions are present when anoxia is well advanced, Windle ( I 944) considered them abnormal. However, an analysis of the research literature (Humphrey, 1953) indicates that a reflex may be weak or strong, but otherwise true to type. A reflex that is absent when the nervous system is intact, however, may be seen when there is damage (Humphrey, 1968a, 1969d). Sometimes also a reflex, such as the Babinski sign, may be a normal part of development during fetal life and for a period postnatally, but indicate brain damage in adult man. General anesthetics, including the barbiturates (Goodman & Gilman, 19651, cross the placental barrier and anesthetize the fetus as well as the mother. Narcotics like morphine, codeine, and other opium derivatives also suppress fetal movements, as do tranquilizers. If such drugs have been administered preoperatively and a general anesthetic used, the fetus may be completely inactive. If, however, a spinal or a local anesthetic is employed, the fetus will be active. Although Demerol enters the placental circulation as do other opium derivatives (Goodman & Gilman, 1965), apparently it is transferred to the fetus more slowly, for Hooker ( 1 952, 1958) noted no depression of fetal reflexes when it was administered approximately an hour preoperatively. Examination of the known effects of such drugs leads to the conclusion that fetal reflexes are either suppressed or diminished, but, as in anoxia and asphyxia, they do not become abnormal. Because the effects of anoxia cannot be eliminated entirely, however, the reflexes elicited under the best conditions may not represent the most recent functional capabilities of the fetus. The true capacity at any age will be demonstrated only when the conditions are optimal. In interpretating data on human fetal behavior, there-

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fore, it must be remembered that the activity that has been demonstrated at any given age level may not represent the full motor potential for the age in question.

V. Activity in Response to Tactile Stimulation of Human Fetuses The following behavioral sequence for human fetuses is based almost entirely on light tactile stimuli as described by Hooker (1942, 1944, 1952; see Section IV, B). Stroking the cutaneous surfaces with graded hair esthesiometers was the common technique employed. In a few cases, a glass rod was used, so some degree of pressure was probably exerted also. Except for fetuses approaching the age of viability, the observations were made with the fetus in an isotonic bath (usually Tyrode’s solution) kept at normal body temperature. Three or more crownrump measurements (CR) were made after the reflexes ceased while the fetus was still in the isotonic bath. These were checked with the tables of Streeter ( 1 920) in determining the menstrual ages used throughout the following account, unless otherwise stated. A. THEPERIODOF WIDESPREADREACTIONS - COGHILL’S TOTALPATTERN

The youngest fetus from which Hooker elicited a reflex by stimulation of the nose-mouth area (the perioral area) supplied by the maxillary division of the trigeminal nerve was 7.5 weeks of menstrual age (20.7 mm). The reflex consisted of contraction of the neck muscles on the side opposite or contralateral to the stimulus with flexing or bending the head away from the stimulator. This is the avoiding reaction of Angulo y Gonzalez (1932), Coghill (1929), Hooker (1952), Humphrey (1952, 1964), and others. Fitzgerald and Windle ( 1942, p. 167) elicited contralateral head flexion “without movements of the trunk and arms” by “strong mechanical stimulation” of the maxillary region of a 20.0 mm embryo for a period of “about 3 minutes.” The 22.6 mm fetus (No. 131) of Hooker’s motion picture series was stimulated after removal from the amnion. Eleven contralateral flexion reflexes were elicited. The single ipsilateral response consisted only of lateral head movement. The contralateral reactions varied from lateral flexion involving the upper trunk, and extending to the pelvic region in one of the reflexes, to muscle contraction in the neck region alone toward the end of the active period. At this age, the hands of the living fetus at rest obscure the mouth with the palms toward the chest and the finger tips close together but not overlapping. The soles of the feet face

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13

each other. The hands uncovered the mouth a trifle in only one of the contralateral flexion reflexes of the 22.6 mm fetus, a shift in position that is clearly due to active backward movement of the arms at the shoulders (arm extension). In the other reflexes, the arms were moved passively with the trunk when it flexed lateralward. The soles of the feet did not separate, even when the pelvis was included in the reflex. Because the soles of the feet pull apart if there is movement at the hip joints (Figs. IB, ID, and 2B), it was concluded that the lower extremities were moved passively in the single reflex showing lateral flexion of the pelvis. This extensive reflex was elicited near the beginning of the observations, whereas most of those restricted to neck and upper trunk flexion were noted toward the end of the activity. Using a probe to exert pressure on the mouth and nose area, Fitzgerald and Windle ( I 942) elicited contralateral neck and trunk muscle contraction in a 22.5 mm human fetus (considered to be affected by anoxemia before the observations began) and stronger stimulation over a greater area of the face resulted in a response of “greater magnitude” with movement of both the arms and legs “with the body at their attachments [p. 1621.” They reported that ipsilateral responses predominated. Probably these reflexes were elicited with the embryo still in the amnion but this point is not clear in their account. Pressure on the amniotic sac with a 23.0 mm fetus inside and with the placenta still attached was reported to cause quick reactions of the extremities and lower trunk, sometimes the arms or the legs alone, or with a stronger tap on the amnion, sometimes together, but no head movements were seen, either at the time the reflexes were elicited or identified in the motion pictures. N o reflexes were obtained from any of these small fetuses (20.0-26.0 mm CR) by stroking or touching the trunk and extremities. The differences between the activity reported by Fitzgerald and Windle and that just described from Hooker’s motion pictures are due in part to the differences in the stimuli used (see Section IV, B) but also to failure to see the slight trunk and head movements when the extremity action is much greater (see Section IX). Twelve contralateral flexion reflexes were elicited by perioral (nosemouth area) stimulation of a 25.0 mrn fetus (No. 4) in Hooker’s series, but none ipsilaterally (Humphrey, 1968a, Table 1). By 26.0 mm CR (Figs. l A , 1C) or 27.1 mm CR (Fig. 2A), the fingers covering the mouth may overlap. In 4 of the reflexes at 25.0 mm, both the hands and the soles of the feet separated, showing that both shoulder and hip girdle muscles contracted. In 3 others, the hands separated, but not the feet, so only the upper limbs moved actively. The remaining 5 reflexes were limited to trunk and pelvic flexion, with neck flexion appearing only once. Rump rotation was seen twice, and lateral flexion of the pelvis was

Fig. 1 . A and B are prints f r o m a motion picture sequence showing contralateral head, trunk, and rump flexion in response to stimulation of the f a c e with a hair esthesiometer (black line across nose). C shows the return t o the rest position, followed immediately by an ipsilateral flexion reflex (D)including rotation of the pelvis as well a s flexion of the head, trunk, and rump. A s part of the contralateral reflex, the mouth opened (arrow on B), but the hands obscure the mouth during the ipsilateral flexion reflex in D . The photographs of the fetus are slightly larger than its 26.0 m m C R length ( N o . 24, 8.5 weeks, menstrual age). The action illustrated in A and B required '/4 second and that shown in C and D just under $5 second. The entire reflex sequence was reproduced by Hooker (1939).

Fig. 2. A and B are prints from a motion picture sequence following stimulation of the face by drawing a hair esthesiometer from the area lateral to the mouth upward over the bridge of the nose of CI 27.1 nim human fetus ( N o . 116, 8.5 weeks, menstrual age). T h e stimulator overlies the nose in A but does not touch it. In addition to a contralateral bending of the head. trunk, and rump there is some pelvic rotation in B. where the mouth is also open (arrow at corner of mouth). the asymmetrical extremity movements include finger spreading, and there is separation of the soles of the feet. The photographs are about 1.5 times natural size and the action shown covered less than h a l f a second. C is a photograph showing the peak action of a comparable contralateral flexion reflex of a 34.3 m m fetus ( N o . 134, 9.5 weeks, menstrual age). Note the more widely open mouth ( a t arrow) and the greater separation of the soles of the feet. T h e photograph is reproduced at about I .3 natural size. Approximately % second elapsed f r o m the beginning of the reflex to the frame reproduced here.

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15

maintained even after the return to position was complete. Probably active mouth opening also accompanied the vigorous reflex in which the soles of the feet separated (Humphrey, 1968a). Many of the contralateral flexion reflexes elicited by perioral stimulation of the active fetuses from 26.0 to 36.0 mm, CR length, included active mouth opening. The head, trunk, and pelvic flexion was accompanied by rump rotation more often in the older fetuses of the group and the extremity movements increased in amplitude and complexity. This is demonstrated by comparison of Fig. 1 A-B with Fig. 2. At 26.0 mm (Fig. 1 ) the upper extremity movements consist mainly of extension at the shoulder, whereas at 27.1 mm (Fig. 2A-B), the arm extension is accompanied by some forearm flexion and flexion at the wrist, and even some spreading apart of the fingers (Fig. 2B). At 9.5 weeks (Fig. 2C, 34.3 mm CR), these upper extremity movements are more pronounced and distinctly asymmetrical. Movement of the lower extremities at 26.0 mm (Fig. 1 B) was limited to sufficient lateral rotation and abduction at the hip joints to separate the soles of the feet slightly and rotate the knees lateralward. The soles of the feet separated farther in slightly older fetuses (Figs. 2 8 and 2C), and study of the motion pictures indicates that both the toes and the fingers sometimes spread apart. However, the toe action could not be documented satisfactorily by photographic prints due to the minute changes in position of these short digits and the separation of the toes even in the rest position (Fig. I 1A-B). Mouth opening constitutes an integral part of the more vigorous contralateral flexion reflexes elicited by perioral stimulation during this period. Active depression of the lower jaw separates the lips, at first only in the midline region (arrow on Fig. 1 B), but in a fetus only a little larger the lips may part slightly as far as the corners. By 9.5 weeks the lips sometimes separate completely to the corners (Fig. 2C). There is a distinct time sequence for the movements in these total pattern reflexes: first the head bends lateralward, then the hands uncover the mouth as the upper extremities move backward at the shoulders, and additional trunk and pelvic movement follows. The mouth may be open when uncovered by the hands, or may open on the succeeding motion picture frame, or may remain closed until the lower extremity action separates the soles of the feet. The mouth closes more slowly than it opens, just as the trunk and extremities return to the original position more slowly than the lateral flexion developed. Beginning mouth closure is not often seen for the hands usually return to their rest position before the change commences (Humphrey, 1968a, Figs. 4-5). When the motion pictures are observed at normal speed, the small differences between these total pattern lateral flexion reflexes are not seen, and the stereo-

16

Tryphena Humphrey

typed character of these reflexes, as emphasized by Hooker (1952, 1958; Humphrey, 1964), is a prominent feature of the reactions during this period. Ipsilateral flexion reflexes were not elicited either so early or so frequently as contralateral responses from the fetuses studied by Hooker and his co-workers. A single ipsilateral reaction, involving head movement only, was recorded from the 22.6 mm fetus although there were 11 contralateral reflexes extensive enough, as a rule, to include trunk flexion. There was enough active extension of the arms at the shoulder joints to move the hands away from the mouth in only 1 reflex. From 8to 10 weeks (25.0-40.7 mm CR, Humphrey, 1968a, Table 1) only 10 of the 208 total pattern lateral flexion reflexes elicited by perioral stimulation were ipsilateral (4.8 %). Mouth opening accompanied over 43 % of the 198 contralateral flexion reflexes, but was seen with ipsilateral reactions only once during this period (at 10 weeks), probably because the ipsilateral hand usually obscures the mouth. Most of the ipsilateral reflexes are less extensive than the contralateral reactions, but in a few instances may be greater (compare Figs. 1A-B and 1C-D). In general, the ipsilateral reflexes appear to be executed more slowly than those contralateral to the stimulus (Humphrey, 1968a). In other words, the negative avoiding reaction, or withdrawal, is a more rapid one than the positive reflex in which the area touched approaches the stimulus (Section V, B, 2 and 3). From 7.5 weeks to 10 weeks of menstrual age, no local reflexes have been elicited from human fetuses by tactile stimuli of cutaneous surfaces. Mouth opening, reported earlier (Hooker, 1952, 1958; Humphrey, 1964, 1966b) as a local reflex at 9.5 weeks has now been shown to occur as part of the total pattern reflexes, as just described (Figs. 1A-B and 2; see also Humphrey, 1968a, 1968b, 1969b, 1969c, 1969d, 1969e). The limb reflexes reported by Fitzgerald and Windle (1942) for 23.0 mm and 26.0 mm fetuses were elicited either by tapping or by pressing on the amniotic sac (Section V, A) not by stimulating the cutaneous surface. Until 10 weeks also, only the areas of the face supplied by the maxillary and mandibular divisions of the trigeminal nerve are sensitive to stimulation. The oral mucosa has not been tested for reflexes, but it may be sensitive to stimuli early because the nerve fibers are closer to the mucosal epithelium than to the cutaneous surfaces at the age when the earliest reflexes have been elicited (Humphrey, 1966b).

B. THEDEVELOPMENT OF LOCALIZED REFLEX ACTIVITY 1. The Transition Period Beginning at the 10.5 week age level (Hooker, 1960), the palms of the

The Development of Human Fetal Activity

17

hands become sensitive to stimulation, then the soles of the feet (1 1 weeks). The upper and lower extremity reflexes elicited by palmar and plantar stimulation are independent of head and trunk reactions (Section V, B, 4). Also there appears to be a decrease in the number and in the amplitude of the reflexes elicited by perioral stimulation at this time (Humphrey, 1968a). However, the motion picture material at 10 to 10.5 weeks is less adequate than either earlier or later, because more of the fetuses were influenced by the drugs given the mother. Consequently, the decrease in activity may be partly due to the effect of the drugs. Nevertheless, the character of the activity changes between 10 and I 1 weeks. The position at rest also differs. The hands no longer cover the mouth but face each other, and the soles of feet face somewhat downward (Figs. 3 and 6). Lower extremity movements are a less consistent part of the total pattern, contralateral flexion reflexes and mouth opening are less frequent. In these reflexes also, the chin occasionally rotates ipsilateralward when the head flexes contralateralward, and the hands may extend instead of flex. By 11 weeks, head, trunk, and pelvic extension reflexes (Fig. 3) often replace the lateral flexion reflexes, particularly when the perioral stimulation is near the midline. No mouth opening accompanies these extension reflexes. At rest (Fig. 3A), the vermilion borders of the lips show, but at the height of the reflex (Fig. 3B) the lips often appear to tighten somewhat or to be compressed (Humphrey, 1968a, 1969d), for the borders almost disappear. Sometimes the lower extremities extend at the hips, knees, and ankles (Humphrey, 1968a, Fig. 8A), but this action may be limited to slight extension at the hips (Fig. 3). The arms may move forward (flexion at the shoulder joints), there may be forearm extension, and the fingers may extend a little. Although there is some variability in response to perioral stimuli, both the head and trunk extension reflexes and the contralateral flexion reflexes are stereotyped (Hooker, 1952). Like the reflexes during the earlier period, these reflexes are characteristic for the age level. On two occasions, mouth opening reflexes were noted at 1 1 weeks in response to pulling the fetus by the umbilical cord with its back toward the substrate. Both of these oral reflexes were accompanied by some lateral head and trunk flexion and by extremity movements (Humphrey, 1968a, Figs. 6-7; 1969d). These reflexes are of particular interest because of the rapid mouth closure and the equal (but slight) separation of the lips at the midline and at the corners. Just prior to this period, there is an increase in development of the superficial muscles about the mouth (Gasser, 1967) which may account for the changed contour of the lips. The quick, snaplike closure indicates that stretch of the muscles of mastication has become an effective stimulus for their contraction.

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Tryphena Humphrey

Fig. 3. T w o photographs showing an extension reflex following stimulation of the lips of an I I-week fetus ( N o . 6 5 , 48.5 m m C R length) when touched by the clamp on the umbilical cord. In A the action has not yet begun. In B the head, trunk, and rump extension is illustrated just after the peak of the reflex was attained when there was some beginning return to the rest position. At its peak, this reflex included also a slight compression of the lips, extension of the left forearm with some j e x i o n at the shoulder, and extension of the lower extremities at both the knees and hips. The reproduction is at ubout I .2 normal size.

The extension reflexes following perioral stimuli decrease in frequency by 11.5 weeks. An initial head extension may be followed by some contralateral head and trunk flexion combined with rotation of the head, and accompanied by rump rotation and approximation of the palms of the hands (Hooker, 1939, plate on p. 43; Humphrey, 1968a Fig. 9). In these reflexes the mouth is open farther at the midline than laterally. From 11.5 weeks onward stimulation of the perioral region usually produces little or no lower extremity activity. The upper extremity action decreases also, but to a lesser degree. Activity is more often limited to the facial area and is more variable. Head movements frequently constitute part of the reaction when the perioral area is stimulated, but movements of the hand largely disappear (Humphrey, 1968a, 1969b, 1969d).

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19

2. Avoiding and Protective Reflexes The first contractions of the cervical muscles on stimulating the perioral area are avoiding or withdrawal reflexes that are potentially protective, for the area touched is moved away from the stimulus (Humphrey, 1964, 1968a, 1969b, 1969c, 1969d). The extensive total pattern contralateral flexion reflexes that involve all extremities also are avoiding as are the head and trunk extension reflexes that follow them. The quick, snaplike mouth openings and closures accompanied by head, trunk, and extremity action at 1 1 weeks have also been considered potentially protective (Humphrey, 1968a, 1969d). As these total pattern reflexes disappear, local reflexes of a potentially protective nature replace them. Stimulation of the eyelids at 10.5 to 1 I weeks elicits a squintlike contraction of the orbicularis oculi muscle. This reflex is the first truly local reflex elicited by stimulation of the face, for at first there is no other activity with this eyelid movement. Slightly later, contralateral head, trunk, and pelvic flexion may accompany the reflex (Hooker, 1952; Humphrey, 1966b). Contraction of the corrugator supercilii may follow stimulation over the eyebrow area to give a scowl-like movement at 1 1 weeks, as a separate reaction at first, but soon combined with the orbicularis oculi action. At 14 weeks the squintlike orbicularis oculi reflex was accompanied by retraction of the angle of the mouth and elevation of the ala of the nose following stimulation upward over the mandible and across the eyelids (Fig. 4). In this reflex, trunk and lower extremity extension may be present or absent (Humphrey, 1968a, Fig. 14). In a 16-week fetus (Fig. 5 ) orbicularis oculi and corrugator supercilli contraction (squintlike and scowl-like reflexes) have been seen combined with slight closure of the lips, with no trunk or extremity movements and only a minute amount of head extension at the end of the reflex. Potentially, at least, reflexes of this type are protective, just as are the avoiding total pattern reflexes during earlier development. Combined with bilateral corrugator action and bilateral retraction of the corner of the mouth, these reactions in animals bare the teeth and produce a ferocious appearance. In human postnatal development they constitute one of the mechanisms for emotional expression.

3 . Reflexes Related to Feeding The first total pattern reflexes related to feeding are the ipsilateral flexion reflexes that bring the perioral area stimulated toward the stimulus (Humphrey, 1964, 1968a, 1969b, 1969d). Ventral head flexion and rotation of the face ipsilateralward serve the same purpose. These positive reactions, in which the area touched approaches the stimulus, have

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Tryphena Humphrey

Fig. 4 . Four frames from a reflex elicited by drawing the stimulator from the cheek (in B). The head extended and flexed or bent to the side opposite the stimulation ( B and C ) , the angle of the mouth retracted, and the upper lip elevated slightly near the corner ( 0 and C ) . Also, the orbicularis oculi muscle contracted so that the ipsilateral eyeball was flattened and the fusion line between the eyelids almost disappeared (Cj. Finally the fuce rotated away f r o m the side stimulated and the mouth opened more widely f D),but without the upper lip elevation seen in 0 and C . The entire reflex, as reproduced by Hooker (1939), shows trunk extension in the lumbosacral region and extension of the lower extremities (between C and D ) . The part reproduced here covered a time span of I !4 seconds. Other reflexes of this 14-week fetus are reproduced in Figs. 13, IS, 17, and 18. Those in this figure are slightly less than 0.4 the size of the fetus. A) upward across both eyelids (in

neither been seen so early prenatally nor occur so frequently as the avoiding reactions (contralateral head flexion, head extension, and rotation of the face away from a stimulus; Humphrey, 1964, 1968a, 1969b, 1969d). Mouth opening (and closure) as part of the total pattern reflexes at 8.5 weeks precedes swallowing. In these reflexes mouth opening is due to contraction of the muscles that lower the mandible (Humphrey, 1954). Until 11 weeks, closure is probably passive, that is, due to relaxation of the muscles, for the time involved is significantly greater than the time for mouth opening (Humphrey, 1968a, 1969b, 1969d). By 1 1 weeks, at least, and also at 12.5 weeks, when the mouth has been seen to snap shut rapidly (Humphrey, 1968a; Figs. 6, 7 and 1 l), evidently closure is sometimes due to a stretch reflex resulting from the pull on the muscles when the jaw is lowered. Swallowing has been reported as early as 12 to 12.5 weeks (Hooker, 1952; Humphrey, 1964, 1968a), and a characteristic reflex at 13 weeks is shown in Fig. 6 following stimulation in the oral area. Slight head extension as the mouth opened and the larynx elevated (Fig. 6B) is fol-

The Development of Human Fetal Activity

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lowed by ventral head flexion as the larynx is lowered and the sternocleidomastoid muscles again became prominent (Fig. 6C). N o other movements occurred in this reflex or in another illustrated previously at 14 weeks (Hooker, 1939; Humphrey, 1968a, 1969d). No tongue movements have been seen or recorded photographically for human fetuses until 14 weeks when protrusion and retraction of the tongue were photographed following hand stimulation (Fig. 7). Head movement accompanied the oral activity, and finger closure followed the hand stimulation (Humphrey, 1968a, 1969c, 1969d). At 15.5 weeks stimulation of the lips and tongue may cause mouth opening (Fig. 8A), tongue elevation with formation of a groove (or trough) running lengthwise (Fig. 8B), and lip closure on the stimulator when the jaw lifted (Fig. 8C), but no other movements. In the swallowing reflexes (Fig. 6) and in mouth closure following hand stimulation (Fig. 7), the action was due to elevation of the mandible by the muscles of mastication. In lip closure on the stimulator (Fig. 8), both jaw and lip movement occurred. Slight protrusion of both lips accompanied by mouth opening has been seen at

Fig. 5. Drawing the stimulator downward over the left eyebrow, the upper and lower eyelids and along the side of the nose in ( A ) elicited muscle action in three areas, allshown in B . Contraction of the cvrrugator supercilii is shown by the less prominent light area over the superciliary ridge ihat gives a scowl-like effect when the movement is seen (compare B with A and C). The contraction vf the orbicularis oculi muscle pattens the eyeball and obscures the fusion line between the eyelids (see arrow on BJ to give a syuintlike effect when seen in motion. The lips at the time of stimulation were slightly parted ( a s in A). then closed slightly (B), and reopened again as the eyebrow and eyelid returned to position, and the head extended a trifle ( C ) .N o other action took place. The time covered by this figure is just vver one second. T h e photographs of this 16-week fetus ( N o . 27. 114.0 m m C R length) are about 0.4 of its size.

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Tryphena Humphrey

Fig. 6 . Part of a swallowing reflex elicited by stimulating the lower lip in ( A ) of a fetus of I3 weeks of menstruul age ( N o . 45, 75.0 mm C R length). The grid shown in these photographs was tried to bring out small differences in position, but wus found to contribute little if anything. Following stimulation, the head extended and the mouth opened f B). As the larynx was elevated, the curve from chin to sternum rounded (see arrow) and the outline of the sternocleidomastoid muscle disappeared. When the larynx descended ( C ) , the head Jexed forward slightly and the outline of the sternocleidomastoid muscle again became clear (see arrow). but the lips remained slightly parted. There were no movements of the extremities or trunk. The action reproduced here required approximately 1 % seconds, and the photogruphs show the fetus at about 0.9 normal size.

16 weeks (Humphrey, 1968a, Fig. 22). The sequence reported by Hooker ( 1 952; Humphrey, 1964) places upper lip protrusion (1 7 weeks) before lower lip protrusion (20 weeks) with simultaneous protrusion and pursing of both lips by 22 weeks. Protrusion of the lower lip with puckering of the upper lip, on stimulation of the lower lip, has also been seen at 20 weeks (Fig. 9) with the tip of the tongue elevated behind the lips (Fig. 9C). Golubewa el al. ( I 959) reported sucking at 24 weeks and at 29 weeks Hooker ( 1 952) noted sucking strong enough to be audible. At what fetal age it is first possible to elicit a gag reflex has not been determined, but possibly much earlier than the one thus far recorded

The Deveiopment of Human Fetal Activity

23

(Fig. lo). Considerable stimulation with a glass rod was required, probably over both the back of the tongue and the posterior wall of the pharynx. N o doubt the stimulus included pressure as well as touch. The gag reflex itself was rapid and rather violent, although it was not accompanied by extremity or trunk activity (Humphrey, 1968a, 1969b, 1969d). Wide mouth opening, laryngeal elevation, spasmodic contraction of the diaphragm, depression of the floor of the mouth (Fig. 1OA-B), and partial mouth closure (Fig. 1OC) all occurred. The changes in facial expression show that some of the muscles of facial expression participated as well as those that lower and raise the mandible.

4. Extremity ReJlexes Until the hands are pulled away from their rest position covering the mouth, the upper extremities are moved passively with the trunk. As soon as the shoulder girdle muscles contract and pull the upper arm

Fig. 7. The mouth opening and tongue elevation and protrusion in A and the partial mouth closure shown in B and C followed stimulation of the palm of the ref! hand of a 14wseek fetus ( N o . 37, 88.5 mm C R length) when amniotic tissue that was caught in the fingers was pulled awa-y by the stimulator ( A and B). After the tissue was removed, the fingers closed tightly IC). The portion of the reflex shown here, from about its peak to a return to position. involved approximately 3% seconds. The photographs are shown at about 0.9 normal size.

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Tryphena Humphrey

Fig. 8. Three photographs illusrruting lip and tongue reflex activity of a 15.5-week fetus ( N o . 135, 107.5 m m CR),following stimulation by pushing the stimulator inside the mouth and moving it from the midline area across the tongue und lips to the corner of the mouth (A and B). Separation of the lips in A rims fvllowed by elevation of the tongue at the sides (light areas between lips) to f o r m a groove or trough in B (dark spot between lips near the midline). I n C, the lips closed tightly on the tim mu la tor when the lower jaw was lifted. N o other activity M ~ U Snoted. T h e period covered by the portion of the rejlex shown is upproximutely % second. The illustrutions show the fetus at about 0.7 normal size.

Fig. 9. Stimulation of the lips of this 20-week fetus ( N o . 55, 166.0 m m C R ) was followed by lip and tongue movements. A t the time of stimulution (A) the upper lip was a1ready IiJied slightly near the corner and the lips were distinctly separated. T h e lips then closed partiully (B) and, us closure becume more complete. the lower lip HWSprotruded and the tongue appeared between the lips (C). In addition, the upper lip puckered, us indicated by the greater prominence of the vertical lines. The outline of the mentalis muscle, identiJiuble in all three photographs, is more prominent in C where the lower lip is pushed outward, or protruded, and the mandible lifted slightly. N o other action took place. The portion of the rej?ex reproduced here was executed in a little under one second. T h e illustrations lire at about 0.4 the size of the fetus.

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Fig. 10. Three stages in a gag reflex elicited f r o m an 18.5-week fetus ( N o . 111, 144.5 m m C R ) by inserting a glass rod fur back in the mouth ,$,here it undoubtedly touched the back of the tongue and probably the posterior phuryngeal wall. T h e action did not begin until over 2M seconds after the rod was inserted, but was then distinctly rapid. i n A. the mouth has opened widely, but % second later it is tlosing on the rod (B). Here the change in the contour in the neck area (see arrow) indicates elevation of the larynx. T h e glass rod has been removed in C . one second later, and the mouth has reopened slightly. The surface outline in the neck region indicates that the larynx is no longer elevated. Although the uction resulting in the gug reflex was rapid, there were no movements of the lower extremities and only a $light amount of extension at the shoulder near the end of the reflex (compare C with A and B). T h e facial expression in A and B is characteristic f o r a gag reflex postnatally. Diaphragmatic spasm may have accompanied the reflex but this could not be determined satisfactorily. The time spanned by the action in this figure is I YZ seconds. and the photographs are a little less than half the size of the fetus.

backward (or extent it), the hands pull apart, then move downward away from the face. Arm extension and some separation of the hands accompanied a few reflexes of a 22.6 mm embryo and in one reflex the mouth was uncovered completely (Section V, A). By 26.0 mm (Fig. 1A-B), 27.1 mm (Fig. 2A-B), and 27.7 mm (Fig. 1 1A-B), the active upper extremity movements that are part of the total pattern contralateral flexion reflexes sometimes include flexion at the wrists (Figs. IB and 2B) and the fingers spread apart (Figs. 2B and 1 I B). Extension at the shoulder (Fig. 2B) is sometimes accompanied by slight forearm extension (Fig. 2C). By 34.3 mm CR (Fig. 2C) all of these movements of the upper extremity are more marked. During this entire period the contralateral

26

Tryphenu Humphrey

Fig. 1 1 . A and B show purr of a contralaterulflexion reflex of a fetus of 8.5 weeks ( N o . 61,27.7 mm C R length). I n A, the reflex has not yet begun and the stimulator still touches the face. I n B. the head and trunk are bent to the side opposite the stimulus: the hands no longer cover the mouth after the arms extended slightly at the shoulders und the hands flexed at the wrists and the fingers spread apart (compare leji hand in A and B). The soles if the feet separated and. when the film is viewed, the toes also appeur to spread apart. but their small size makes it impossible to document rhis motion from still pictures. I n a partial full face view like the one in B, it is not possible to determine whether the mouth is open. Part of a refex elicited within the amnion is shown in C . The small v-shaped area at the arrow is the open mouth. I n this reflex also, the fingers spread apart and the soles of the feet separated bur again it is not possible t o determine whether the toes separared beyond the position at rest. The time spunned in A and B is about 1/4 second. The fetus is shown u t about twice the normal size. In C, the letters am touch the border of the amnion.

flexion reflexes that include these active upper extremity movements are elicited only by stimulation of the perioral areas supplied by the maxillary and mandibular divisions of the trigeminal nerve. At 10.5 weeks and perhaps earlier (Hooker, 1938, 1952, 1958; Humphrey, 1964, 1969b, 19694 the palms of the hands become sensitive and stimulation over the shoulder has been followed by movement in the underlying joint. These first reactions to palmar stimuli consist of incomplete finger flexion usually without participation of the thumb (Hooker, 1938 and later) and with an almost equally rapid return to position. At 1 1 weeks flexion at the wrist and elbow, medial rotation of the upper arm, and forearm pronation may all accompany the partial finger closure (Fig. 12). By 12 weeks the fingers no longer flex equally, the thumb may

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27

move a little or not at all, and the extent of flexion of the hand has decreased. By 13 to 14 weeks, finger flexion following palmar stimulation may be either complete or incomplete (Fig. 13) with some fingers flexed very little. and others more (Fig. 13B-C). Shortly afterward ( 1 5- 15.5 weeks) finger closure may be maintained for a short time. By 18.5 weeks a weak grasp has developed (Fig. 20A). At first the thumb lies outside the closed fingers (Fig. 20A) but may be within (Fig. 21A) o r outside of the fingers by 23.5 weeks (Fig. 2 1 B). Grasp at this time is stronger and in the youngest viable fetus of this series (27 weeks) grasp was almost strong enough to support the entire body weight. In some instances, stimulation of the palm of the hand at 14 weeks has elicited other reflexes in conjunction with movements of the digits and the hand. One of these reactions to palmar stimulation consisted of mouth opening, tongue protrusim and withdrawal, and ipsilateral face turning, followed also by finger closure (Fig. 7). Another and different reflex followed drawing the hair esthesiometer across the palm of the hand of another fetus of 14 weeks. In this reflex, the fingers closed, the face turned away from the hand stimulated, the upper lip on the ipsilateral side retracted, and the lower lip was lifted (Humphrey, 1 9 6 9 ~ )In . neither reflex were there movements other than those of the head, the

Fig. 12. Incompleiefinger closure elicited by stimulating the palm of the hand of a fetus of I I weeks of mensirual age ( N o . 26, 48.5 mm C R length). In A , the stimulator is still in contact with ihe hund. but no longer iouches it in B. Note ihai a s ihe fingers pariially closed in B and C ihey moved alike and there was no movement of the thumb. although there waspexion of ihe hand itself, the arm moved backward at ihe shoulder, and the forearm changed posiiion. In D. the fingers have reiurned to their original position. Except for the finger and arm movement on ihe side stimulated, there M ~ noS oiher action. This entire repex was shown by Hooker (1939). T h e part reproduced here required slighily over one second. T h e illustrations are about 0.8 normal size.

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Tryphena Humphrey

Fig. 13. Partialjinger closure elicited by stimulating the palm of the hand of a fetus of 14 weeks, menstrual age ( N o . 13, 88.5 m m C R length). Following the stimulation (A), the third to jifth digits moved ( B ) before the index.finger (C). but3nger closure was not complete and in this reflex the third digit moved differently than the fourth andjifth. Toward the completion of the action (D), the forearm Jlexed and supinated slightly and the arm rotated medialward to bring the two hands opposite each other. This reflex was reproduced in greater detail by Hooker in 1939. The part shown here required I 1% seconds. The photographs show the fetus at less than half its true size.

oral area, and the hand stimulated. These reflexes illustrate the close relationship found perinatally and postnatally between oral activity and hand movements. The similarity to the Babkin and palmomental reflexes has been discussed elsewhere (Humphrey, 1969c, Figs. 16- 17). The lower extremities also move passively at first, due to the flexion of the lower trunk and pelvis. The soles of the feet face each other and are partially in contact by 22.0 mm. Although the contralateral flexion reflex of the 22.6 mm fetus that included arm extension was also accompanied by lower trunk flexion and pelvic flexion, there was no separation of the soles of the feet. However, sufficient movement in the hip joints (lateral rotation and abduction) to pull the feet apart did occur in at least 3 of the 13 contralateral flexion reflexes at 25.0 mm in which lateral pelvic flexion was greater than at 22.6 mm. Active movement of the lower extremities, therefore, like that of the upper limbs, begins as part of the total pattern lateral flexion reflexes elicited by perioral stimulation. At 8.5 weeks (Figs. l B , 2A-B, and I I ) , the soles of the feet separate farther, as the extent of movement in the hip joints increases, and a

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lesser amount of action may appear at the knee and probably at the ankle joints (Fig. 2B). In the motion pictures, the toes appear to spread apart slightly when the fingers separate (Fig. 1 1 B), but the shortness of the toes and their separation at rest (Fig. 1 I A ) make it impossible to demonstrate this movement satisfactorily with photographs (Fig. 1 1 B). All of these lower extremity movements take place as part of the total pattern lateral flexion reflexes elicited by perioral stimulation before a n y surfaces of the lower extremity are sensitive to stimulation. The sole of the foot was reported to respond to stimulation as early as 10.5 weeks (Hooker, 1952, 1958; Humphrey, 1964), but these reflexes have not been verified from the motion picture films (Hooker, 1960). However, plantar sensitivity to stimulation is consistently present at 1 I weeks. The first reflexes observed (Hooker, 1952, 1958) consist of plantar flexion of the toes without other action. By 11.5 weeks, the plantar toe flexion may be accompanied by flexion of the foot (Fig. 14) and flexion at the knee and hip. By 11.5 weeks also dorsiflexion of the great toe and fanning of the other toes sometimes follows plantar stimulation. Dorsiflexion of the foot, and flexion at the knee and hip joints may be included in the Babinski reflexes (Fig. 15) or the action be limited to movements of the digits. During the earlier age levels, the plantar flexion reflex is elicited more frequently than the Babinski reflex, but later dorsiflexion of the great toe with fanning of the other digits predominates (Hooker, 1952, 1958; Humphrey, 1964, 1969b, 1969~). As a rule, action following stimulation of the sole of the foot is limited to these ipsilateral lower extremity reactions. On rare occasions, however, responses other than lower extremity movements have been elicited. One of these reflexes was an exceedingly rapid but complete mouth opening and closure at 12.5 weeks, accompanied at the time only by slight lateral head flexion (Humphrey, 1968a, Fig. 11) although followed almost immediately by a kick on the side stimulated. In another instance, stimulation of the sole of one foot of a 14-week fetus (Fig. 16A) was followed by a series of movements that included wide mouth opening two times by depressing the lower jaw (Figs. 16B and 16D), with closure and swallowing between them (Fig. 16C). Rapid action of both upper and lower extremities also occurred (Fig. 16B-D) as well as some ventral head flexion (Fig. 16D), marked head, trunk, and rump extension (Fig. 16C), and flattening of the abdominal wall with flaring of the rib cage in an inspiratory gasp. This reflex is of particular interest for it includes action of almost all regions in which movements have been elicited at this age, as do the total pattern reflexes of the first 2.5-3 weeks of fetal activity (7.5-10 or 10.5 weeks).

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Tryphena Humphrey

Fig. 14. A plantarflexion reflex elic,ited by stroking the sole of the right foot of a I3week fetus ( N o . 45, 75.0 mm C R length) with the stimulutor. T h e position at rest is shown in A. where the stimulutor touches the sole of the f o o t as shown by the arrow. In B , there is plantar flexion, both of the toes and the foot. These movements becume more marked in C . There was evidently some flexion ut the knee, f o r the left leg was curried backward, but no other movements were demonstruted. The photogruphs in this figure cover an interval of I !4 seconds. The fetus is shown at approximutely normul size.

C. FUNCTION OF FETALREFLEXES

Opinions differ concerning the function of reflexes during fetal life. Some experimental embryologists believe that development proceeds normally according to a predetermined genetic pattern regardless of whether function occurs (Hamburger, 1963, 1964; Jacobson, 1966; Weiss, 1937, 1941a, 1941b). The literature is far too extensive to review here. The role of genetic factors in early development is well established, but whether function influences development and, if so, the point where the influence begins is difficult to determine and probably varies

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throughout phylogeny. In lower vertebrates, neural function appears to be of little significance for normal development, as shown by the experiments of Harrison (1904) and others (see Hooker, 1952, p. 107; Humphrey, 1966a, p. 266). For the most part, however, the evidence favoring the concept that function does not affect development is limited to experiments on the spinal cord or brain stem of lower vertebrates in which the postoperative effects were followed for only a relatively short period (Weiss, 194 I b, 194 lc). Long-term experiments have demonstrated that when the postoperative observation time is extended the animals do not remain completely normal (SzCkely & Szenthgothai, 1962; Weiss, 194I b, p. 7 1). SzCkely and Szentigothai suggested that the departure from normal behavior is probably related to the involvement of higher

Fig. IS. Three stages in N Babinski reflex elicited by stroking the sole of the right f o o t of a fetus of 14 weeks of menstruul age ( N o . 13, 88.5 m m C R length). The stimulator (dark line) touches the sole o f t h e f o o t in A. In E. thejrumefolloMing !he peak of the repex, the toes ore still in motion slightly. but the great toe is cleurly dorslflexed. a s is also the f o o t . T h e flexion ut the knee and hip seen in E is increased in C. in which fanning of the toes hus appeared. T h e portion o f the rejlex shown here took plmce in h a l f o second. T h e return to the resting position u'as m u c h slower, f b r the entire wflex U S shown by Hooker ( I 939) required approximtrtely three seconds. I n thisJigirre the ,fetus is uhorrt 0.7 norniul size.

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Tryphcna Humphrey

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centers of the nervous system. Because both development and function proceed from cervical spinal cord levels cephalad, abnormalities of function that depend on higher centers are not likely to appear during short term experiments. The observations of Gottlieb (1965, 1968) demonstrate that either depriving duck embryos of auditory stimuli, or increasing the amount of exposure to them, alters the responses to auditory stimuli after hatching. Following hatching, increased auditory stimulation also enhances the responses (Gottlieb, 1966, 1968). Satisfactory evidence for comparable effects of stimuli on mammalian fetuses is difficult to secure and not available. Postnatally, however, both functional and structural neural effects of sensory deprivation (Held & Bauer, 1967; Scherrer & Fourment, 1964) and sensory enrichment have been demonstrated (Diamond, Lindner, & Raymond, 1967; Rosenzweig, Krech, Bennett, & Diamond, 1962). I t would be surprising indeed if the effects of function were to begin at the arbitrary point of birth (or hatching). It seems more logical to assume that lowering the excitatory threshold of the neurons when function of the fetal neural circuits begins (Gottlieb, 1968, p. 170) leads to their more frequent activation, and that, in consequence, development will be modified to some degree throughout the remainder of fetal life as well as postnatally. According to Windle (1940, p. 164) there is “scanty evidence” that any fetal movements demonstrated outside of the uterus occur normally in utero due to lack of stimulation, especially during the early stages of development. However, there is nu evidence that they do not occur. Inasmuch as fetuses are more readily stimulated when the oxygen supply is good (Fitzgerald & Windle, 1942) and reflexes have been demonstrated outside of the uterus (Hooker, 1944, 1952, 1958; Windle, 1940, 1944) as early as 7.5 weeks and spontaneous activity that needs no stimulus by 8.5-9.5 weeks, it would be surprising if no movements occurred within the uterus during this period. Although there are differ-

Fig. 16. Four illustrations showing the major part of the action in a complex reflex elicited by drawing the stimulator f a t arrow in A) d o n g the sole of the left foot of u fetus of 14 weeks of menstrual aye ( N o . 37, 85.5 mm C R length). In B. the upper extremities are Jlexed ut the shoulders, the elbows. and the rc-rists. and the lower extremities are in motion slightly. I n addition. the head is bent forward a little and the mouth is open. In C , there is marked head and trunk extension with closure of the mouth and elevation of the larynx (note prominence at arrow), accompanied by extension of both upper and lower extremities to a variable degree at all major joints. In C. the mouth has reopened and the head, trunk. und extremities are returning toward their original position. The action illustrated in this figitre reyuiredJust over two seconds. The illitstrations are about 0.8 normal size.

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Tryphena Humphrey

ences in the amount of stimulation (Humphrey, 1953, 1966a), stimuli are not completely absent except for gravity effects (Reynolds, 1962). Since a slight increase in the carbon dioxide level heightens the excitability outside of the uterus, fluctuations in the carbon dioxide level in utero may also provide stimulating effects (Section IV, C). During early development when the uterus is in the bony walled pelvic cavity, pressures from adjacent viscera could be transmitted through the uterine wall and the amniotic fluid to the fetus, especially when there is increased intraabdominal pressure due to coughing, bending, and other movements of the mother (Humphrey, 1966a). On passing through the amniotic fluid, the minor surface pressures will be intensified and have widespread effects. The greater degree of activity noted by Fitzgerald and Windle (1942) in response to tapping on the amnion, as compared with the reflexes elicited by Hooker after removal, support this suggestion. In one instance also, Hooker found that a 10 mg esthesiometer was adequate to elicit two extensive reflexes (including mouth opening, Fig. I IC) by pressure on the amnion, but was not equally effective immediately after removal. Stronger stimuli may have been necessitated by the decrease in the oxygen supply after removal of the amnion, but the brief time interval makes it unlikely that this was the only factor involved. Turning now to the question of a possible function served by specific fetal reflexes during development, the following points might be mentioned. Mouth opening reflexes on perioral stimulation of human fetuses begin slightly before the tongue is withdrawn from between the palatal shelves (Humphrey, I968b, I969e). These mouth opening reflexes aid in tongue withdrawal through pull on the tongue when the jaw is depressed. Suppression of this activity, or even delay, would slow the change in position of the palatal shelves and so increase the likelihood of the epithelial fusion of the tongue and the palatal shelves that was shown experimentally for rats (Steffek, King, & Derr, 1966). There is no evidence, as yet, that reflex retraction of the tongue (His, 1901) as well as depression of the jaw plays a part in palatal closure. However, the growing nerve tips are closer to the base of the mucosal epithelium of the mouth than to the epithelium of the lips (Humphrey, 1966b) when the perioral area becomes sensitive to stimulation. Therefore, pressure of the large tongue against the oral mucosa might easily provide sufficient stimulation to cause reflex withdrawal from between the palatal shelves. Tongue reflexes do begin at a comparable period of development in other mammals, such as the rat (Angulo y Gonzalez, 1932), and were seen as spontaneous movements of macaque fetuses within the amnion by Bodian ( 1 968) before they were elicited by stimulation. Swallowing was reported by Hooker (1944, 1952) to begin at about

The Development of Human Fetul Activity

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12.5 weeks. At I3 weeks (Fig. 6) and at 14 weeks it is more frequent if either the lips or the inside of the mouth are stimulated. Possibly swallowing develops as early as 10.5 weeks, as was reported earlier (Hooker, 1954, 1958; Hooker & Humphrey, 1954), but the reflex seen at that age was not verified photographically. Probably closing the mouth on the amniotic fluid leads to the beginning of swallowing even earlier, for the external nares are already plugged with epithelium when mouth opening begins and for a long time after swallowing is well developed (Humphrey, 1969e). Swallowing reflexes of normal fetuses have been shown radiographically in utero by 12 weeks of “gestation age [Davis & Potter, 19461.” These reflexes serve to maintain the level of amniotic fluid, evidently by absorption through the gastrointestinal mucosa, for fetuses with atresia of the esophagus or anencephalic fetuses that cannot swallow (Pritchard, 1965) develop hydramnios (Hamilton, Boyd, & Mossman, 1962). Arshavskiy ( 1 959) suggested that the substances swallowed in the amniotic fluid serve a nutrient function, as had Preyer many years earlier ( 1885). Because the gut returns from the umbilical cord to the abdominal cavity in fetuses of 42.0 to 48.0 mm in C R length (Hamilton et ul., 1962), or between 10 and 1 1 weeks of menstrual age, it is tempting to speculate that swallowing reflexes may play some part in its rotation and return to the abdominal cavity. The suggestion is supported, in part at least, by the fact that the cranial loop of the gut returns before the caudal one. Possibly also the swallowing reflexes may be a factor in the resolution of the excessive growth of esophageal and upper intestinal epithelium that takes place during the tenth week of menstrual age (toward the end of the second month, fertilization age, Patten, 1968, p. 384), and so be significant also in the recanalization of these regions of the gastrointestinal tract. One might also theorize concerning the value of orbicularis oculi contraction in separating the fused eyelids, concerning the role of reflex spreading apart of the fingers (and probably toes) in preventing minor fusion between the digits, and concerning the part played by extremity movements in the development of the joints. In this connection, however, there is some experimental evidence that immobilization leads to ankylosis and other skeletal deformities (chick, Drachman & Coulombre, 1962; Hamburger & Waugh, 1940) and some orthopedic surgeons (Badgley, 1943; Drachman & Banker, 196 I ) consider that joint deformities of infants are the result of immobilization during fetal life. Whether or not any or all of these postulations concerning the function of fetal reflexes in normal development may prove correct, fetal activity certainly strengthens the muscles during prenatal life.

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Tryphena Humphrey

D. THERELATIONOF SUPPRESSION (OR INHIBITION) OF ACTIVITY TO THE DEVELOPMENT OF BEHAVIOR The total pattern reflexes elicited by perioral stimuli from 7.5 to 10.5 weeks become less frequent thereafter, and mouth opening gradually becomes independent of trunk and extremity activity. The change is effected by the suppression of the latter reflexes through inhibition of the reflex arcs centrally in a caudorostral sequence (Section V, B, 1 ; also Humphrey, 1968a, 1969b, 1969d). Inhibitory synaptic end bulbs are present both on the dendrites and on the somata of neurons (Bodian, 1966; Walberg, 1968), and there are also special inhibitory regions in the central nervous system such as the bulbar reticular inhibitory center (Magoun & Rhines, 1946), and parts of the cerebellum, of the striatal complex, and of the cortex (Ruch, Patton, Woodbury, & Towe, 1961). In the cervical spinal cord of fetal monkeys, Bodian ( 1 968) found that the F-type synaptic end bulbs, which he concluded to be inhibitory in function, increased sharply in number just before the period of “secondary, integrated local reflexes [Bodian, 1968, p. 1241,” which is comparable to the period of suppression of the total pattern reflexes and the appearance of local reflexes and combinations of reflexes in human fetuses. Because brain stem levels are the most important regulatory centers during early phylogeny, probably the differentiation of bulbar and midbrain regions is responsible for the transition from total pattern reflexes to local reflexes during this early period of ontogenetic development. First the total pattern reflexes must be largely suppressed; then localized reflexes and functional reflex combinations are possible. In suppressing the total pattern reflexes, their neural arcs are retained, not lost. Therefore, these reflex arcs are activated by perioral stimuli when anoxia and asphyxia set in at these ages (Section IV, C) or under various other circumstances thraughout development (Section VIII). When suppression of the gross movements begins, local reflexes and functional reflex combinations are few. By 14 weeks, however, a wide range of reflexes has appeared in which the lower extremity and trunk are completely inactive, but the head and some upper extremity movements may remain. Fetuses at 14 weeks are extremely active, and sometimes a stimulus sets off activity in almost all parts of the body. Probably this peak of activity is reached at the height of midbrain regulation, just before higher brain areas in turn suppress and regulate the midbrain centers. Three illustrations of these reflexes follow. One is a reaction to plantar stimulation at 14 weeks (Fig. 16). Even swallowing was included in this total pattern type of action, although ordinarily swallowing is not accom-

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panied by trunk or extremity movements, only head extension and flexion (Fig. 6). In another instance, a comparably widespread, but quite different reflex resulted from stroking the back from the lower spine up to the neck (Fig. 17). The resulting trunk and head extension, shoulder elevation, mouth opening, inspiratory gasp, and upper and lower extremity movements constitute a total type of reaction that clearly resembles a postnatal reaction to tickling. Another reflex elicited from the same 14-week fetus followed chance contact of a glass rod with the genital area in changing the position of the fetus (Fig. 18). At least the genitofemoral groove and the base of the penis were stimulated (Fig. 18B), and light pressure was probably applied as well as touch. Among the movements that followed were marked head extension with mouth opening, then closing, and rapid movements of all extremities. Although these reflexes do not involve all of the neuromuscular system capable of functioning at this age level, they do include the head, trunk, extremity, and lower jaw movements of the total pattern reflexes at the height of their development and, incorporated with them, other motor activities

Fig. 17. Part of a reflex sequence following stimulation of the back by drawing a hair esthesiometer upward from the lumbosacral area to the neck. In A the stimulator (shown by arrow) is touching the midscapular region. T h e reaction involved both extension and twisting of the trunk, head extension with slight rotation, elevation of the shoulder on the side toward the observer, and lifing the opposite leg. A n inspiratory gasp accompanied the mouth opening in B and C . This fetus (No.13, 88.5 m m C R length) is shown here a t approximately half the normal size. The time spanned by the action in this jigfigure is about one second. The entire reflex, which required about 2% seconds, was reproduced by Hooker in 1939.

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Tryphena Humphrey

Fig. 18. Three photographs f r o m a motion picture sequence following touching the genital area with a glass rod when the position of the fetus was changed. T h e reaction of this fetus ( N o . 13. 88.5 mm C R length, 14 weeks, menstrual age) involved extension and slight rotation of the head with mouth opening ( B ) and closing ( C ) two times, flexion of the upper extremities at the shoulders, elbows, and wrists with some Jinger flexion and hand adduction, and complex lower extremity movements that differ on the two sides ( B and C ) . From the time of stimulation in A to an approximate return to the original position involved about 2% seconds. The action covered in the presentfigure (A, B and C ) was executed in just over one second. The illustrations are at approximately 0.6 normal size.

that have been added by 14 weeks. At this age, however, the stimuli not

only activate earlier total pattern reflex pathways, but also additional neural circuits for the various newly acquired local reflexes and reflex combinations. Between 15 and 16 weeks, the fetuses become relatively inactive (Hooker, 1952, 1960) and the few reflexes elicited by facial stimuli usually involve only the oral area and head (Fig. 8). From 18 weeks until the fetuses can be resuscitated temporarily, there are few reactions. This period of sluggishness has been ascribed by Barcroft and Barron (1 937) to the reduced oxygen supply resulting from the rapid growth at 18- 19 weeks and later. After artificial respiration is established at 23.5 weeks and later (Figs. 1 9 , 2 l ) , there is a period of marked activity during which almost any stimulus may set off movements of the head, trunk, and extremities. Indeed, from this period into postnatal life it is often uncertain what activity is directly related to a specific stimulus. After

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resuscitation also, the characteristic scowl, the tight eyelid closure, the wide mouth opening, and the tongue position of the “pain cry [WaszHockert, Lind, Vuorenkoski, Partanen, & ValannC, 19681” are present (Fig. 19). Although the lower oxygen supply after the fetal increase in size may account for the reduction in activity, reflexes are decreasing in frequency before there is much change in size. Therefore, the initial decrease in aciivity is probably due in large part to the inhibitory effects of neural circuits through the dorsal thalamus and striatal complex, which again must first suppress the activity through the midbrain IeveIs, in part at least, before imposing the higher level pattern of function on the final common pathways of the brain stem and spinal cord. At this time the motor activity becomes typical of striatal function, with progression movements of the extremities a conspicuous part of the action. These automatic associated movements via the striatal complex must, in turn, come under the inhibitory, or regulatory, control of the cerebral cortex, so that localized actions appropriate to the sensory input become possible. As Kuo (1967, p. 92) indicated for the adult when he wrote “in any given response of the animal to its environment . . . the whole organism is involved” the greater part of the neural activity is frequently the suppression (or inhibition) of most of the potential overt action in order to allow specific, discrete, localized, purposeful acts to take place. The

Fig. 19. Photographic prints from four successive frames of a motion picture sequence of a nonviable premature infant of 23.5 weeks of menstrual age for which breathing was initiated with a resuscitator. When the mask was removed f r o m its f a c e , the infant cried ( A and B). Note the typically tightly closed eyelids and the position of the tongue in crying f i n B) with the tip turned upward. Crying is ceasing and the mouth closing in C and D , where the line between the eyelids is again clear when the orbicularis oculi muscle relaxed. These smallprints, only aboui 0.1 the size of this 205.0 m m premature infant ( C R length), show the eyebrow clearly only in D so evidently the corrugator supercilii also contracted t o produce a scowl while crying.

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brain-damaged spastic child or the one with choreiform movements is not able to execute the essential movements of everyday living, because he cannot sufficiently suppress and regulate the gross activity. E. POSTNATAL REPETITIONOF FETALREFLEX ACTIVITYSEQUENCES

Although the repetition of fetal activity sequences and their probable anatomic basis were discussed in some detail earlier (Humphrey, 1969c), the structural arrangement of the central nervous system that determines this repetition is worthy of emphasis here. Two main factors are involved. The first is the arrangement of the motor neurons that innervate the skeletal muscles in a longitudinal somatotopic pattern (Section VI I I ) extending from the upper midbrain (oculomotor neurons) to the ventral horn neurons of the last sacral segment of the spinal cord. Thus the head muscles are innervated primarily by the brain stem motor neurons and the neck, trunk, and upper and lower extremity muscles by motor neurons arranged in the proper cervicocaudal order throughout the spinal cord. The second factor is the order of development of the neural tube. Closure begins in the upper cervical region and proceeds caudally and rostrally from this area (Kingsbury, 1924). Therefore, the motor neurons mature and become functional, except for minor variations, in the same general order (Humphrey, 1954, 1969~).An obvious variation in brain stem development rostrally concerns the motor neurons of the trigeminal and facial nerves, for those that participate in mouth opening reflexes mature earlier than do the other motor nerve cells of these nerves (Jacobs, 1970). Both the structural and the functional order of development at spinal cord levels progress from cervical (neck and upper extremity) through thoracic (trunk) and lumbosacral (lower extremity) levels. These longitudinally arranged motor neurons constitute the final common path of Sherrington (1 906) over which all activation of skeletal muscles must be transmitted. Therefore, not only the total pattern reflexes are executed over them, but also both the facilitatory and the inhibitory effects from all levels of the central nervous system. Because both the sequence of maturation and the order of functional activity are established with the development of the primary (Humphrey, 1953, p. 9) or fundamental (Sherrington, 1906, p. 320) reflex arcs by the order of neuronal maturation, and “all the other neural arcs” are superimposed on them, the descending fiber tracts from higher brain centers will establish functional relationships in the same general order that the reflexes developed. Upper spinal cord levels will be reached (and regulated) by descending tracts before they grow into lumbosacral levels, whether

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they arise in bulbar, midbrain, striatal, or cortical areas. Consequently, the general sequence of development of the activity is repeated, although the character of the individual actions changes. One of the most obvious examples of this repetition of motor sequences is found in the development of grasping (Hooker, 1938, 1952, 1958; Humphrey, 1964, 1969~).Partial finger closure in which all fingers move alike (Fig. 12) is followed by more complete finger closure with variable finger movement (Fig. 13). The thumb takes no part at first, but later thumb action is included (Fig. 21), closure becomes complete, and grasp increases in strength. Perinatally and postnatally the infant again demonstrates partial finger closure before variable finger action and thumb movements appear, but the activity at this age is regulated from the extrapyramidal cortical areas by multisynaptic pathways through the striatal complex and the midbrain tegmentum. When voluntary control begins, partial finger closure is again the first type of finger movement, thumb participation appears later, and grasp follows. Apposition of the thumb and the forefinger, a movement not yet seen prenatally, is the last refinement of finger movements to develop. At each central nervous system level of regulation, the developmental sequence is repeated, but at each level also the complexity and variability of action increase to culminate in the fine individual movements that are possible only through the function of the motor area of the cortex.

VI. Fetal Activity in Response to Other Types of Stimuli In addition to the light tactile stimuli used by Hooker to elicit most of the activity already described, pressure directly on the fetus or pressure on the amnion were used by Fitzgerald and Windle (1942). As pointed out by Hogg (1941), even lightly stroking the surface probably produces some slight deformation of the growth cones when the nerve fibers still lie below the epithelium. Heavy pressure would have a similar effect when the nerve tips are still farther from the surface. Pressure on the amnion is not only intensified on transmission to the fetus, but affects many areas, including both sides of the fetus if it is moved by the pressure. This difference in the strength and in the extent of the stimulation is probably as significant a factor in the amount of activity noted by Fitzgerald and Windle (1942) as the better oxygen supply which they emphasized. Only a relatively few attempts were made by Hooker to elicit reflexes by stretch stimuli, as reported by Windle and his collaborators for other mammals (Windle, 1934, 1944). Reflexes of this type were not reported

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by Fitzgerald and Windle (1942) in their observations on small human fetuses (20.0-26.0 mm CR, or 7.5-8.5 weeks of menstrual age by the tables used by Hooker). However, such reflexes were identified for the arm and hand at 9.5 weeks by Hooker (1939, 1952, 1958), two weeks after the first reactions to tactile stimuli. Possibly in the cat, such reflexes do appear earlier than those from tactile stimuli, as reported by Windle and Griffin (193 l ) , but as yet there is no evidence that this is true for human fetuses. In the total pattern reflexes elicited by perioral stimulation from 7.5 to 9.5 weeks, stretch stimuli evidently do not cause the return to position because a distinctly longer time is required than for the muscle contraction itself (Humphrey, 1968a, Figs. 4-5). At 1 1 weeks and again at 12.5 weeks sufficiently rapid mouth closure was seen (Humphrey, 1968a, Figs. 6-7 and 1 1 ) to indicate that stretch must have been the effective stimulus to close the jaw so quickly. Perhaps stretch stimulation is also a factor in producing the characteristic postural changes that take place at about this time in development, for static stretch reflexes maintain posture in the adult. This postural change also begins at about 9.5 weeks and by 1 1 weeks both the upper and lower extremities have a different position at rest than at 8.5 weeks (compare Figs. 1A and 2A with Fig. 3). In the development of sensory modalities in birds, Gottlieb (1968, p. 154) listed touch stimuli as effective before vestibular excitation and proprioceptive stimuli from muscles following vestibular sensitivity. However, for some mammals vestibular reflexes have not been demonstrated until after the body righting reflexes are present (sheep, Barcroft & Barron, 1937, 1939; cat, Windle & Fish, 1923). According to Minkowski (1928) vestibular reflexes begin as early as 10 weeks in human fetuses. Hooker (1942, 1944) interpreted two reflexes following rolling a fetus of 9.5 weeks as vestibular in origin, but later (Hooker, 1952, 1958) concluded that they were probably body righting reflexes. Minkowski ( 1928) found that the lateral vestibular nucleus differentiated early. By 10 weeks the neurons of this nucleus are slightly better differentiated than the best developed nerve cells in the upper cervical spinal cord a week after the first reflexes involving them have been recorded (Humphrey, 1965, p. 55). Also the sensory neurons of the vestibular ganglia at this age are as well developed as the best differentiated cells of the semilunar ganglia a week after function begins. If the sensory receptors and the synaptic connections of the vestibular reflex arcs are functional also, vestibular reflexes should be present by 9.5 weeks. The reflexes first reported by Hooker ( 1 942, 1944) at 9.5 weeks as vestibular consisted of rapid lateral flexion of the trunk accompanied by

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upper and lower extremity movements bilaterally. This type of reaction indicates integration of the vestibular stimuli into the existing functional neuronal network of the total pattern reflexes in human fetuses, as Coghill ( 1930) believed for Amblystoma. Indeed, certain vestibular stimuli cause an essentially total reaction of the infant (Moro reflex, Prechtl, 1965). Even in the adult, a vestibular stimulus may set off a total body reaction. There are two points of view concerning the question of self-stimulation. Gottlieb and Kuo (1965) reported that the duck embryo is constantly stimulated by its own activities, including both touch and auditory stimuli from its own vocalizations. However, Hamburger et al. ( 1966) were in sharp disagreement concerning the role of self-stimulation in the development of chick embryos. Among mammals, except for human fetuses (Humphrey, 1969b), the question of self-stimulation has received little attention. In view of the position of the fetal hands covering the mouth during the time that the total pattern contralateral flexion reflexes are at their peak of development (8.5-9.5 weeks; Figs. I , 2, 1 1 , 22), stimulation of the perioral area (the only skin area sensitive during this period) could scarcely be avoided in the confined space within the amnion. Later in development, also, the hands are often near the face, and the thumb frequently touches the lips (Figs. 20A, 2 0 0 Because the mouth is often open after 14 weeks, the thumb can easily slip inside (Fig. 20B), especially when the fetus is confined within the amnion as shown in the photographs of Nilsson (1965). Sucking does not occur at this time, however, for puckering the lips, a necessary part of sucking, does not begin until 22 weeks (see Section V, B, 3). Therefore, thumb sucking before birth, as reported by Murphy and Langley ( 1963), for example, must take place toward the end of gestation. Because little is known about the function of the other sensory modalities before the age of viability, they will not be considered. An extensive account is given in the review by Carmichael ( 1954).

VII. Spontaneous Activity The term spontaneous activity was used by Minkowski (1928) and by Hooker (1944, 1950, 1952, 1954, 1958, 1960) to denote activity for which the stimulus, if any, was unknown. The term was used in the same way by Angulo y Gonzalez ( 1 932) and by Windle and his associates (Windle & Griffin, 1931; Windle & Orr, 1934; Windle et al., 1933). Considerable attention was focused on whether spontaneous movements in mammals like the cat developed earlier than reflexes, as Tracy (1 926)

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Fig. 20. Three photographs selected to show the hand-mouth positional relationship often seen at this period of development (18.5 weeks, menstrual age) and even earlier, as well as later. This is the same fetus f o r which parts of a gag reflex are shown in Fig. 10. I n A the right hand of thefetus is grasping a glass rod and in B thefingers have loosened on the rod. In A also the Left thumb is pressed against the upper lip, but in B it is inside the upper lip. Both hands are close to the mouth in C with the left thumb behind the upper lip and apparently against it. T h e index Jinger lies against the nose near the hair esthesiometer, the black line that touches the tip of the nose. A t this age neither the upper nor the lower lip has been seen to purse (or pucker) and although the thumb may enter the mouth. sucking has not been demonstrated at this age.

found for the toadfish. The term spontaneous activity, as used by Comer (1964; Corner & Bot, 1967), by Hamburger (1963, 1964; Hamburger el al., 1965, 1966) and by Hughes (1966; Hughes et al., 1967) applies only to periodic, rhythmic motor discharges of endogenous origin that depend either on the “automatic, self-generated discharge of neurons [Hamburger, 1963, p. 3501” of genetically determined motor patterns or on chemical stimuli. In other lower vertebrates, as well as in fishes, spontaneous movements appear before reflexes can be elicited. In the aglossal toad, Xenopus luevis, spontaneous activity develops into swimming (Hughes & Prestige, 1967) before any cutaneous area becomes sensitive to stimulation. In another toad (Eleutheroductylus, Hughes, 1966), the earlier

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developing spontaneous activity builds up independently to diagonal walking, whereas reflexes develop into bilateral swimming. In frogs, also, Youngstrom ( 1938) found that spontaneous movements appeared before reflex activity. In both the lizard (Lacerta vivipara; Hughes et al., 1967) and the turtle (Tuge, 193 I ) , spontaneous movements also appear before reflexes, by a difference of two days in the lizard and at least several hours in the turtle. In the study of avian behavioral development, spontaneous movements appear some time before reflexes and constitute a large part of the activity. They have been described for the pigeon (Tuge, 1934), the chick (Hamburger, 1963, 1964; Hamburger & Balaban, 1963; Hamburger et al., 1965, 1966; Kuo, 1932; Orr & Windle, 1934), and the duck (Gottlieb & Kuo, 1965), although certain differences in the time of development and in the character of the activity were found by the different investigators. Spontaneous activity has received less attention in the behavioral studies on mammals. Windle and Griffin (193 1) reported a sequence of development in cat fetuses that indicated a possible relationship to righting reflexes. Spontaneous activity was found later in development than reflexes in the rat (Angulo y Gonzalez, 1932), but earlier in sheep (Barcroft & Barron, 1939), and in cat fetuses (Coronios, 1933; Windle & Griffin, 1931). Later, however, Windle et al. (1933) reported local reflexes to be the earliest observed activity of cat fetuses. Bodian ( 1968) found no difference between the time that spontaneous activity and reflexes appeared in macaque fetuses. Spontaneous activity was not mentioned by Fitzgerald and Windle ( 1 942) for the 20.0-26.0 mm human fetuses that they observed and Hooker (1960, p. 436) did not see spontaneous movements until 9.5, or possibly 8.5 weeks. For human fetuses spontaneous movements were usually present only at the beginning of the activity (Hooker, 1952, 1960; Minkowski, 1928) until after resuscitation became possible. Although the available information is by no means satisfactory, there appears to be a trend throughout phylogeny (with the exception of birds) for spontaneous activity to be reduced in amount and to be manifested progressively later in development. Thus, in the macaque spontaneous movements coincide with reflexes in time of development (Bodian, 1968), and for human fetuses the evidence at present indicates that spontaneous movements do not develop until a week to 2 weeks after reflex activity. In human fetuses, either the endogenous neural activity does not build up sufficiently early in development to discharge spontaneously prior to reflex activity or there is an initial period of inhibitory regulation of spontaneous discharges by the sensory input, with discharge set off later by the

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sensory stimuli. At certain periods in human development (for example, 8.5-9.5 weeks and 14 weeks) the fetuses are particularly active and spontaneous movements are seen more often. Upon resuscitation, spontaneous progression movements (Fig. 21) are nearly continuous at times and almost any stimulation sets off head, trunk, and extremity action of the same type as the spontaneous movements.

VIII. The Relation of Integration to the Development of Behavior Integration of activity is achieved in two fundamental ways. One is by the synaptic end bulbs on the motor neurons constituting Sherrington’s final common path. The other consists of the central nervous system areas (or centers) in which sensory impulses are brought together and from which discharge is made over efferent circuits to the appropriate motor neurons of this final common path. Integration by the first process is operative through the inhibitory and excitatory synaptic boutons and the chemical mediators from the onset of reflex action throughout the course of development. The second integrative mechanism begins somewhat later when sensory centers of increasing complexity differentiate in the brain stem, the dorsal thalamus, and the cortex. Sensations from within the fetus, as well as from the external environment (Hooker, 1960), are integrated in these areas. Integration at the synaptic level becomes effective as soon as sensory impulses from the environment are transmitted to enough motor neurons to elicit a response. Closing the neural circuit brings the fetus and its environment into relation with each other, as well as the site of the stimulus into relation with the muscles that respond. This unification begins with the first reflex, and all reactions that follow become integrated into the existing neural circuits when they are first executed. Endogenous spontaneous movements that are unrelated to any sensory stimuli, however, are neither integrated nor coordinated. When the sensory input is transmitted to more motor neurons and the reflexes increase in intensity or in extent (or both), the additional neural activity is likewise integrated when function begins. The development of the S-type excitatory synaptic boutons on the dendrites of spinal motor neurons in monkeys (Bodian, 1966, 1968) probably occurs in human fetuses during the development of the total pattern reflexes, and the dramatic increase in the Ftype inhibitory synapses on somata should coincide with the period during which these total pattern reflexes are suppressed and local reflexes appear.

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Fig. 21. Two photographs f r o m a motion picture sequence involving rapid extremity movements of the 23.5-week premature infant illustrated in Fig. 19. Almost any stimulation was followed by quick rhanges in the position of the arms and iegs with the hands opening and closing, either with the thumb inside of the fingers (B) or outside ( A ) .Similar movements occurred without known stimulation. In B , the deep inspiratory movement is shown by the depressed sternum, the elevated rib cage, and the flattened abdominal wall.

Stretch stimuli are not integrated into the behavior pattern in the same way as are those from the external environment (exteroceptive stimuli) and those from the internal environment (visceral afferent stimuli). The two-neuron stretch reflex arcs close later than the polysynaptic reflex arcs of exteroceptive (and probably visceral afferent) reflexes (sheep, Barron, 1944; chick, Hamburger, 1963, 1964; Scharpenberg & Windle, 1938; cat, Windle, 1931; human embryos, Windle & Fitzgerald, 1937). Static stretch reflexes build up into posture and those of kinetic type become the tendon reflexes (see Humphrey, 1953). Integration is closely linked with the complex muscle spindles and their interrelations with the motor neurons, These sensory receptors develop relatively late as compared with the simple receptors for general tactile sensitivity (Hogg,

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1941; Humphrey, 1966b), for Cuajunco (1940) did not find them distinguishable from motor endings in the biceps brachii muscle until 11 weeks, although primitive sensory terminals on large muscle fibers were identified at 10 weeks by Hewer (1935; see also Humphrey, 1964). The groups of neurons or nuclei that receive sensory impulses from all parts of the body and head constitute the centers of integration in which the different types of sensory impulses, and those from different body areas, come together and are correlated or integrated. Whereas the motor neurons that constitute the final common path have a longitudinal somatotopic pattern in the central nervous system (or topographic representation of the body parts innervated by them; Section V, E), the neurons that receive the various types of incoming sensory impulses from cutaneous surfaces, from tendons, from joints, and from the viscera have somatotopic patterns that are essentially transversely arranged. The earliest developing center of integration, and the most primitive one, is situated at the junction of the spinal cord with the medulla where the nuclei of the dorsal funiculus, the gray matter of the dorsal horn of the spinal cord, and the nucleus of the spinal tract of the trigeminal nerve are arranged in a sacral to ophthalmic pattern from the dorsomedial to the dorsolateral border of the medulla-spinal cord junction area, corresponding to the pattern formed by the fibers that terminate there (Humphrey, 1955, 1969a). By the time that the total pattern lateral flexion reflexes include active mouth opening and active extremity movements (8.5 weeks), all of these somatic fiber systems and the general visceral afferent fibers of fasciculus solitarius have grown into this region (Humphrey, 1952, 1955). However, all reflexes at this age, and until after 9.5 to 10 weeks, are elicited only by stimulation of the perioral area supplied by the trigeminal nerve. There are no investigations that indicate at what age the bulbar inhibitory and facilitatory areas and the superior collicular level of the midbrain become dominant integration centers for human fetal activity. Evidently the change is accomplished gradually during the period that the extremities become sensitive to stimuli (or local extremity reflexes appear), local reflexes in the facial areas develop, and functional combinations of reflexes arise (from about 10.5 to 14- 15 weeks). At 15 to 16 weeks, another period of reduced activity begins, probably by inhibitory effects through the association nuclei constituting the thalamic centers of integration and their discharge to motor neurons of the final common path through the striatal complex. The coordinated progression movements of the extremities that make up much of the activity of premature and full-term infants are characteristic of the function of these neural circuits through the dorsal thalamus and striatal complex.

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Integration at cortical levels begins postnatally with the inhibition and regulation of the automatic movements from the striatal complex. The first areas for cortical integration are the somesthetic association cortex that relates touch with other general sensations, and later the association areas related to the special senses, such as the auditory association cortex. From these cortical association areas impulses are discharged for the response appropriate to the major stimuli reaching them, first over multisynaptic extrapyramidal pathways (gross movements), then over direct corticospinal (and corticobulbar) tracts (fine movements). The prefrontal cortex constitutes the highest center of cortical integration where past experience, decisions, and similar activities begin in childhood. So far as overt behavior is concerned, however, integration in this area probably results more often in suppression of activity than in action.

IX. Other Considerations Often the basis for differences in views on the development of behavior can be determined if one seeks for them. The early reports on small human embryos, like the accounts of Strassman (1903) and Yanase (1907), mention only extremity movements. In the ovoid confined space within the amnion only the extremity activity may be seen, for the amount of head and trunk movement is reduced and not easily detected, even with motion pictures. However, when photographic prints of fetuses within the amnion are examined closely, head and trunk action are demonstrable also (26.0 mm, Fig. 22). Slight lateral flexion away from the observer (compare A and B of Fig. 22) may be followed by extension of the head and trunk (compare A with C). The conspicuous part of the activity, however, and the only portion seen on examination of the motion pictures at normal speed, is the arm movement that pulls the hands away from the mouth, and lower limb movement, if both are present (Fig. 11C). Neither the open mouth nor the trunk movement is seen. Tapping on the amnion may move the fetus and so stimulate the side away from the observer by pushing the face against the substrate. Such stimuli probably result in a reflex ipsilateral to the tap on the amnion, but contralateral to what was probably the stimulus that elicited the reflex. In the development of behavior, Coghill emphasized the integrated reaction of the entire organism to its external environment. However, because the earliest response to external stimulation is confined to the neck region due to the limited neuromuscular development, this reflex

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Fig. 22. Three prints from a mntion picture sequence of a reflex elicited by pressure of the stimulator (dark line) on the surface of the amnion of the 26.0 mm fetus illustrated in Fig. 1. A und B ure from cnnsecutive frumes and C is the sixth frame in the series taken at 24 frames per second. In the beginning movement in B. the arms have moved just enough to uncover the nose und there is a beginning lateral flexion 10 the side opposite the stimulutnr. In C. the trunk movement has changed to exiension (see text). The soles of the feet did nor separute in this reflex us they do in equally extensive reflexes outside of the amnion. The open mouih is indicuied by the arrow.

has been, and continues to be, confused with the local reflexes that appear later in development (Section V, B). The gradual spread of the reaction from flexure in the neck region to rump flexure is clear for human fetuses, but is compressed into so short a period that this fact is easily missed without motion picture recording (Section V, A). For an equally short period the upper and lower limbs are moved only passively with the trunk as it flexes, without the contraction of limb muscles. The earliest extremity muscle contraction also moves the limbs as part of the total reaction of the fetus and so constitutes a further elaboration, or expansion, of the total pattern reflex. Even the digits spread apart and the mandible is depressed to open the mouth. All of this activity is in response to stimulation of the perioral area, and only this area. In seeking to understand the development of behavior and the mechanisms involved, various pitfalls await the enthusiast who focuses his attention too sharply on one facet of the problem, whether it be the genetic patterns involved- to the exclusion of function-or the synaptic relations of individual neurons-to the neglect of the overall sequential

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changes in the nervous system as a whole. Differences in the development of behavior are to be expected throughout vertebrates. If rapid, automatic, stereotyped activity is the significant factor in determining survival, as in fishes, spontaneous movements play a major role. For reptiles, and especially for birds, rhythmic spontaneous activity also is important in behavioral development. When mammalian postnatal survival depends on early ability to stand and run, the extremity reflexes develop early, as in the sheep and guinea pig, and there is a more or less complete suppression of the total pattern reflexes. For the infant monkey that must soon cling to its mother’s fur for survival, arm movements and grasp appear early. For the completely helpless human infant, for whom specialization appears to be lacking, the total pattern reaction of the fetus is more fully developed and retained for a significantly longer period than for the other mammals that have been studied.

ACKNOWLEDGMENTS The author is greatly indebted to Miss Blanche Page Cushman and Mrs. Gwen Barnett for their technical assistance in the preparation of the illustrations and the manuscript. She is also deeply indebted to Dr. Elizabeth C. Crosby for her helpful suggestions and criticisms. REFERENCES Angulo y Conzalez, A. W.The prenatal development of behavior in the albino rat. Journal of Comparative Neurology, 1932,55, 395-442. Anokhin, P. K. Systemogenesis as a general regulator of brain development. Progress in Brain Research, 1964, 9. 54-86; discussion, 99- 102. Arshavskiy, 1. A. Mechanisms of the development of nutritional functions during the intrauterine period and following birth. Journal of General Biology ( U S S R ) , 1959, 20, 104-1 14. Badgley, C. E. Correlation of clinical and anatomical facts leading to a conception of the etiology of congenital hip dysplasias. Journal of Bone and Joint Surgery, 1943, 25, 503-523. Barcroft, J., & Barron, D. H. Movements in midfoetal life in the sheep embryo. Journal of Physiology (London), 1937,91, 329-35 I . Barcroft, J . , & Barron, D. H. The development of behavior in foetal sheep. Journal of Comparative Neurology, 1939,70,477-502. Barron, D. H. The early development of the sensory and internuncial cells in the spinal cord of the sheep. Journal of Comparative Neurology, 1944,81, 193-225. Bodian, D. Development of the fine structure of the spinal cord in monkey fetuses. 1. The motoneuron neuropil at the time of onset of reflex activity. Bulletin of the Johns Hopkins Hospital, 1966, 119, 129- 149. Bodian, D. Development of fine structure of spinal cord. 11. Pre-reflex period to period of long intersegmental reflexes. Journal of Comparative Neurology, 1968, 133, 1 13- 166.

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Gottlieb, G. Species identification by avian neonates: Contributory effect of perinatal auditory stimulation. Animal Behaviour, 1966, 14, I8 1-290. Gottlieb, G. Prenatal behavior of birds. Quarterly Review of Biology, 1968, 43, 148- 174. Gottlieb, G., & Kuo, Z.-Y. Development of behavior in the duck embryo. Journal of Comparative and Physiological Psychology, 1965, 59. 183- 188. Hamburger, V. Some aspects of the embryology of behavior. Quarterly Review of Biology, 1963,38,342-365. Hamburger, V. Ontogeny of behavior and its structural basis. In D. Richter (Ed.), Comparative neurochemistry. New York: Macmillan (Pergamon), 1964. Pp. 2 1-34. Hamburger, V., & Balaban, M.Observations and experiments on spontaneous rhythmical behavior in the chick embryo. Developmental Biology, 1963, 7 , 533-545. Hamburger, V., Balaban, M., Oppenheim, R., & Wenger, E. Periodic motility of normal and spinal chick embryos between 8 and 17 days of incubation. Journal of Experimental Zoology, 1965, 159, 1-14. Hamburger, V., & Oppenheim, R. Prehatching motility and hatching behavior in the chick. Journal of Experimental Zoology, 1967,166, 17 I - 104. Hamburger, V., & Waugh, M. The primary development of the skeleton in nerveless and poorly innervated limb transplants of chick embryos. Physiological Zoology, 1940, 13, 367-380. Hamburger, V., Wenger, E., & Oppenheim, R. Motility in the chick embryo in the absence of sensory input. Journal of Experimental Zoology, 1966,162, 133- 160. Hamilton, W. J., Boyd, J. D., & Mossman, H. W. Human embryology. (3rd ed.) Baltimore: Williams & Wilkins, 1962. Harrison, R. G. An experimental study of the relation of the nervous system to the developing musculature in the embryo of the frog. American Journal of Anatomy, 1904, 3, 197-220. Held, R., & Bauer, J . A., Jr. Visually guided reaching in infant monkeys after restricted rearing. Science, 1967, 155, 71 8-720. Hewer, E. E. The development of nerve endings in the human fetus. Journal of Anatomy, 1935.69, 369-379. His, W. Beobachtungen zur Geschichte der Nasen- und Gaumen-bildung beim menschlichen Embryo. Abhandlungen der Mathematisch-physischen Klasse der Konigliche Sachsischen Akadernie der Wissenschaften, 1901,27,349-389. Hogg, I. D. Sensory nerves and associated structures in the skin of human fetuses of eight to fourteen weeks of menstrual age, correlated with functional capability. Journal of Comparative Neurology, I94 1,75,371-4 10. Hooker, D. The origin of the grasping movement in man. Proceedings of the American Philosophical Society, I938,79,597-606. Hooker, D. A preliminary atlas of early human fetal activity. Pittsburgh: Author, 1939. Hooker, D. Fetal reflexes and instinctual processes. Psychosomatic Medicine, 1942, 4, 199-205. Hooker, D. The origin of overt behavior. Ann Arbor: University of Michigan Press, 1944. Hooker, D. Neural growth and the development of behavior. In P. Weiss (Ed.), Genetic neurology. Chicago: University of Chicago Press, 1950. Pp. 212-213. Hooker, D. The prenatal origin of behavior. f 8 t h Porter Lecture. Lawrence, Kans.: University of Kansas Press, 1952. Hooker, D. Early human fetal behavior, with a preliminary note on double simultaneous fetal stimulation. Research Publications, Association for Research in Nervous and Mental Disease, 1954,33,98- 113. Hooker, D. Evidence of prenatal function of the central nervous system in man. James

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Arthur lecture on the evolution of the human brain. New York: American Museum of Natural History, 1958. Hooker, D. Developmental reaction to environment. Yale Journal of Biology and Medicine, 1960,32,43 1-440. Hooker, D., & Humphrey, T. Some results and deductions from a study of the development of human fetal behavior. Gazeta Midica Portuguesa, 1954.7, 189- 197. Hughes, A. Spontaneous movements in the embryo of Eleutherodacrylus rnartinicensis. Nature, 1966,211, 5 1-53, Hughes. A,, Bryant, S. V., & Bellairs, A. d’A. Embryonic behaviour in the lizard, Lacerta vivipara. Journal of Zoology, 1967,153, 139- 152. Hughes, A., & Prestige, M. D. Development of behaviour in the hindlimb of Xenopus laevis. Journal of Zoology, 1967, 152, 347-359. Humphrey, T. Primitive neurons in the embryonic human central nervous system. Journal of Comparative Neurology, 1944.81, 1-45. Humphrey, T. lntramedullary sensory ganglion cells in the roof plate area of the embryonic human spinal cord. Journal of Comparative Neurology, 1950.92, 333-399. Humphrey, T. The spinal tract of the trigeminal nerve in human embryos between 7% and 8% weeks of menstrual age and its relation to fetal behavior. Journal of Comparative Neurology, 1952,97, 143-209. Humphrey, T. The relation of oxygen deprivation to fetal reflex arcs and the development of fetal behavior. Journal of Psychology, 1953.35, 3-43. Humphrey, T . The trigeminal nerve in relation to early human fetal activity. Research Publications, Association for Research in Nervous and Mental Disease, 1954. 33, 127-154. Humphrey, T. Pattern formed at upper cervical spinal cord levels by sensory fibers of spinal and cranial nerves. Relation of this pattern to associated gray matter. A.M.A. Archives of Neurology and Psychiarty, 1955.73. 36-46. Humphrey, T. Some correlations between the appearance of human fetal reflexes and the development of the nervous system. Progress in Brain Research, 1964, 4, 93- 135. Humphrey, T. The embryologic differentiation of the vestibular nuclei in man correlated with functional development. In International symposium on vestibular and oculomoior problems. Tokyo: Japan Society for Vestibular Research, 1965. Pp. 5 1-56. Humphrey, T. Correlations between the development of the hippocampal formation and the differentiation of the olfactory bulbs. Alabama Journal of Medical Sciences, 1966, 3, 235-269. (a) Humphrey, T. The development of trigeminal nerve fibers to the oral mucosa compared with their development to cutaneous surfaces. Journal of Comparative Neurology, 1966, 126,91-108. (b) Humphrey, T. The development of mouth opening and related reflexes involving the oral area of human fetuses. Alabama Journal of Medical Sciences, 1968,5, 126- 157. (a) Humphrey, T . The dynamic mechanism of palatal shelf elevation in human fetuses. Anatomical Record, 1968. 160, 369. (b) Humphrey, T. The central relations of the trigeminal nerve. In E. A. Kahn, E. C. Crosby, R. C. Schneider, & J. A. Taren, Correlative neurosurgery. (2nd ed.) Springfield, Ill.: Thomas, 1969. Pp. 477-492. (a) Humphrey, T. Function of the nervous system during prenatal life. In U. Stave (Ed.). Physiology of the perinatal period. New York: Appleton-Century-Crofts, 1969. (b) Humphrey, T. Postnatal repetition of human prenatal activity sequences with some suggestions on their neuroanatomical basis. I n R. Robinson (Ed.), Brain and earl) behaviour. New York: Academic Press, 1969. Pp. 43-71. (c)

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Humphrey, T. Reflex activity in the oral and facial area of human fetuses. In J. F. Bosma (Ed.), Second symposium on oral sensation and perception. Springfield, Ill.: Thomas, 1969. Pp. 195-233. (d) Humphrey, T. The relation between human fetal mouth opening reflexes and closure of the palate. American Journal of Anatomy, 1969, 125, 3 17-344. (e) Jacobs, M. J. The development of the human motor trigeminal complex and accessory facial nucleus and their topographic relations with the facial and abducens nuclei. Journal of Comparative Neurology, 1970, 138, I6 1- 194. Jacobson, M. Starting points for research in the ontogeny of behavior. In M. Locke (Ed.), Major problems in developmental biology. New York: Academic Press, 1966. Pp. 339-383. Kingsbury, B. F. The significance of the so-called law of cephalocaudal differential growth. Anatomical Record, 1924,27,305-321. Kuo, Z.-Y. Ontogeny of embryonic behavior in Aves: 1. Chronology and general nature of behavior of chick embryo. Journal of Experimental Zoology, 1932.61, 395-430. Kuo, Z.-Y. The dynamics of behavior development. An epigenetic view. New York: Random House, 1967. Magoun. H. W., & Rhines, R. An inhibitory mechanism in the bulbar reticular formation. Journal of Neurophysiology, 1946, 9, 165- 17 1 . Mall, F. P. On the age of human embryos. American Journal of Anatomy, 1918, 33, 397-422. Mavrinskaya, L. F. On correlation of development of skeletal muscle nerve endings with appearance of motor activity in human embryo. Arkhiv Anatomii Gistologii i Embriologii, 1960,38, 61 -68. Minkowski, M. Uber Bewegungen und Reflexe des menschlichen Foetus wahrend der ersten Halfte seiner Entwicklung. Schweizer Archiv f i r Neurologie und Psychiatrie. 1920.7, 148-151. Minkowski, M. Neurobiologische Studien am menschlichen Foetus. In E. Abderhalden (Ed.), Handbuch der biologisches Arbeitsmethoden, 1928, Abt. V. Teil 5B, Heft 5, Ser. 253, 5 1 1-6 18. Murphy, W. F., & Langley, A. L. Common bullous lesions-presumably self-inflictedoccurring in utero in the newborn infant. Pediatrics. I963,32. 1099- 1 10 I . Nilsson, L. Drama of life before birth. Life, 1965.58.54-69. Orr, D. W., & Windle, W. F. The development of behavior in chick embryos: the appearance of somatic movements. Journal of Comparative Neurology, 1934,60,27 1-285. Patten, B. M. Human embryology. (3rd ed.) New York: McGraw-Hill, 1968. Prechtl, H . F. R. Problems of behavioral studies in the newborn infant. In D. S. Lehrman, R. A. Hinde, & E. Shaw (Eds.), Advances in the study of behavior. Vol. I . New York: Academic Press, 1965. Pp. 75-98. Preyer, W. Specielle Physiologie des Embryo. Leipzig: Grieben’s Verlag, 1885. Pritchard, J. A. Deglutition by normal and anencephalic fetuses. American Journal of Obstetrics and Gynecology, 1965, 25, 289-297. Ranson, S. W. The anatomy of the nervous system. (7th Ed.) Philadelphia: Saunders, 1943. Reynolds, S. R. M. Nature of fetal adaptation to the uterine environment: a problem of sensory deprivation. American Journal of Obstetrics and Gynecology, 1962. 83, 800-808. Rosenzweig, M. R., Krech, D., Bennett, E. L., & Diamond, M. C. Effects of environmental complexity and training on brain chemistry and anatomy: a replication and extension. Journal of Comparative and Physiological Psychology, 1962, 55, 429-437.

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Ruch, T. C., Patton, H. D., Woodbury, J. S., & Towe, A. L. Neurophysiology. Philadelphia: Saunders, 196 I . Scharpenberg, L. G.. & Windle, W. F. A study of spinal cord development in silverstained sheep embryos correlated with early somatic movements. Journal of Anatomy, 1938,72,344-35 1 . Scherrer, J., & Fourment, A. Electrocortical effects of sensory deprivation during development. Progress in Brain Research, 1964,9, 103- 1 12. Sherrington, C. S. The integrative action of the nervous system. New Haven, Conn.: Yale University Press, 1906. Smith, K. U . , & Daniel, R. S . Observations of behavioral development in the loggerhead turtle (Caretta caretta). Science, 1946,104, 154- 155. Steffek, A. J., King, T. G., & Derr, J. E. The comparative pathogenesis of experimentally induced cleft palate. Journal of Oral Therapeutics and Pharmacology, 1966, 3,9- 16. Strassman, P. Das Leben vor der Geburt. Sammlung Klinischer Vortrage, Neue Folge, 1903. No. 353 (Gyndkologie, No. 132), 947-968. Streeter, G. L. Weight, sitting height, head size, foot length and menstrual age of the human embryo. Contributions to Embryology (Publications of the Carnegie Institution), 1920, 11, 143- 170. Swenson, E. A. The simple movements of the trunk of the albino rat. Anatomical Record, 1928.38, 31. Swenson, E. A. The active simple movements of the albino rat fetus: the order of their appearance, their qualities, and their significance. Anatomical Record, 1929, 42, 40. Sztkely, G., & Szentigothai, J. Reflex and behaviour patterns elicited from implanted supernumerary limbs in the chick. Journal of Embryology and Experimental Morphology, 1962.10, 140-151. Tracy, H. C. The development of motility and behavior reactions in the toadfish (Opsanus tau). Journal of Comparative Neurology, 1926, 40, 253-369. Tuge, H. Early behavior of the embryos of the turtle, Terrapene Carolina (L.), Proceedings ofrhe Society for Experimental Biology and Medicine, I93 I , 29,52-53. Tuge, H . Early behavior of the embryos of carrier-pigeons. Proceedings of the Society for Experimental Biology and Medicine, 1934,31,462-463. Walberg, F. Morphological correlates of postsynaptic inhibitory processes. Wenner-Gren Center International Symposium Series, 1968, 10, 7- 14. Wasz-Hockert, O., Lind, J., Vuorenkoski, V., Partanen, T., & ValannC, E. The infant cry. A spectrographic and auditory analysis. Clinics in Developmental Medicine No. 29. London: Heinemann and Lavenham, Suffolk, Eng.:Lavenham Press, 1968. Weiss, P. Further experimental investigations on the phenomenon of homologous response in transplanted amphibian limbs. IV. Reverse locomotion after the interchange of right and left limbs. Journal of Comparative Neurology, 1937,67,269-3IS. Weiss, P. Nerve patterns: the mechanics of nerve growth. Growth, 1941,5, 163-203. (a) Weiss, P. Self differentiation of the basic patterns of coordination. Comparative Psychological Monographs, 1941, 17, 1-96. (b) Weiss, P. Does sensory control play a constructive role in the development of motor coordination? Schweiterische Medizinische Wochenschrif, 1941, 71, 591 -595. (c) Weiss, P. Nervous system (neurogenesis). In B. H. Willier, P. A. Weiss, & V. Hamburger (Eds.),Analysis of development. Philadelphia: Saunders, 1955. Pp. 346-401. Windle, W. F. The neurofibrillar structure of the spinal cord of cat embryos correlated with the appearance of early somatic movements. Journal of Comparative Neurology, 1931,53,71-113.

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AROUSAL SYSTEMS A N D INFANT HEART RATE RESPONSES'

Frances K . Graham and Jan C . Jackson UNIVERSITY OF WISCONSIN

I. I N T R O D U C T I O N ............................................ A. AROUSAL SYSTEMS .................................... B. OR-DR D I F F E R E N T I A T I O N I N A D U L T SUBJECTS . . . . . . . 11.

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P R O C E D U R E ................................................ A. I N F A N T SUBJECTS ...................................... B. LABORATORY A R R A N G E M E N T S ........................ C. H R RESPONSE MEASUREMENT .........................

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DEVELOPMENTAL S T U D I E S O F E V O K E D H R RESPONSE . . . A. NEWBORN H R RESPONSE ............................... 8. H R RESPONSE IN O L D E R I N F A N T S ..................... C. FACTORS A F F E C T I N G T H E D E V E L O P M E N T A L S H I F T . .

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IV. SUMMARY A N D DISCUSSION REFERENCES

'Preparation of this paper, and much of the research described, was supported by grants HD01490 and K05-MH-21762 from the National Institutes of Health and by a predoctoral Public Health Fellowship to the junior author. Computer services were provided through grant FRO0249 to the Laboratory Computing Facility and an N S F grant through the University of Wisconsin Research Committee. 59

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I.

Introduction

Several writers have recently proposed that there are two arousal systems which affect behavior differently, one energizing response while inhibiting receptive and consolidative processes, and the other facilitating these processes and, thus, memory and learning. Sokolov’s work, in particular, has stimulated considerable interest but attention has been largely focused on the facilitative “orienting” system to the neglect of an opposite-acting “defense” system. The present paper considers briefly the evidence from adult studies that these two systems can be distinguished by the direction of heart rate (HR) change. It next reviews typical procedures and problems encountered in studies of infant H R response, and then reviews the data from these studies to determine whether there is a developmental shift from primarily defensive reactions during the newborn period to increasingly probable and larger orienting reactions with increasing age. A. AROUSAL SYSTEMS

Arousal or activation level is an important concept in psychology because it is believed to affect a wide variety of psychological processes. It has generally been viewed as a unitary dimension which could range from low levels during coma or deep sleep to high levels during alert wakefulness or agitation. However, the unidimensionality aspect is being vigorously challenged by recent work. Lacey (1967) has reviewed a number of the findings which pose critical problems, including low intercorrelations among autonomic measures of arousal, evidence for dissociation among central, behavioral, and autonomic measures, and specificity of autonomic “arousal” responses as a function of stimulus situations. In reply, Malmo and BClanger (19671, major proponents of unidimensional arousal theory, have argued that the theory may still be valuable as a general description; and they note that some confusion has arisen because relatively long-term background changes are not separated from discrete, short-term responses. It is the former which are relevant to activation theory, in Malmo’s usage at least. While the unidimensionality argument may not be resolved for some time, it is probably not an all-or-nothing matter, but, like many earlier arguments concerned with general versus specific factors, a question of the relative proportions of variance that can be accounted for by a single common factor in comparison with the variance accounted for by the sum of specific factors. Another approach, exemplified in a recent review article by Routten-

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berg (19681, asks, essentially, whether a larger proportion of variance can be accounted for by two arousal systems than by a single one. Routtenberg suggests that many neurophysiological findings can be better accommodated by postulating two mutually inhibiting arousal systems which have different functions. The first, evoked by high intensities of stimulation and associated with the Moruzzi and Magoun (1949) reticular activating system, functions to energize response and limit the effects of stimulation. The second, evoked by low to moderate intensities of stimulation and involving the limbic system, is assumed to prolong the effects of stimulation and thus to facilitate memory and learning processes. Routtenberg’s theory, while primarily directed to neurophysiological data, has many features in common with Sokolov’s conceptualization (1963) of two generalized reflex systems, labeled a defense reflex (DR) and an orienting reflex (OR). The DR, like Routtenberg’s first arousal system, is evoked by high intensity stimuli and functions to limit the effects of stimulation. The OR is similar to Routtenberg’s second arousal system. It is evoked by “novel” and by “signal” stimuli that are below the intensity sufficient to evoke defense and it functions to enhance the effects of stimulation and in the strengthening of associations. With repeated presentations of an initially novel, non-signal stimulus or after a signal-event connection is fully established, the OR can no longer be evoked. Sokolov has not attempted to identify in any detail the neural structures that might be associated with the two systems. Subcortical areas are assumed capable of initiating either reaction but separate loci have not been elaborated although Lynn ( 1966), in discussing Sokolov’s theory, cites evidence from other investigators that is compatible with involvement of limbic structures in eliciting an OR and of brain-stem reticular formation in eliciting a DR. While not specifying subcortical mechanisms, Sokolov does argue that the cortex plays an important role in amplifying or habituating the OR. He postulates a 2-stage model in which the cortex acts as a comparator-analyzer of incoming stimuli and subcortical mechanisms amplify or dampen the response depending on signals fed back from the cortex. Other theories have also emphasized a fundamental distinction between the effects of high and low-moderate stimuli. Schneirla ( 1 959) cites historical precedents and himself advances a dual system which has communalities with those discussed above. Most importantly, he also relates the system evoked by low-moderate intensity stimuli to facilitative functions. Berlyne (1967), in his most recent discussion of activation theory, recognizes a similar distinction between what he calls re-

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ward and aversion systems. These are explicitly related to Schneirla’s and Sokolov’s concepts. While there are many differences among these various approaches, the important similarity is that they all propose different and, at least in some respects, opposed functions depending on whether stimulus intensity is low or high. If there are two arousal systems with differential effects on such psychological processes as learning and perception, development of these arousal systems during early infancy becomes a matter of interest. It would be expected that the system facilitating “information processing” and mediated by higher nervous system mechanisms would be relatively less developed at birth than the system concerned with energizing and protective functions and mediated by the relatively mature reticular formation. If this is true, further study of the factors influencing development of a facilitating system might aid in understanding why early learning is relatively slow and in determining the conditions under which it could be maximized. The present paper surveys studies of infant HR and discusses, in more detail, studies from our laboratory which are relevant to the question of whether there are developmental differences in the ease of evoking the two arousal systems. For several reasons, the question has been formulated within the framework of Sokolov’s theory. The theory describes objective criteria for distinguishing an OR from a DR and it is based on a substantial body of experimental work employing psychophysiological techniques with human subjects. Such techniques are well suited to the study of infants. B. OR-DR DIFFERENTIATION I N ADULTSUBJECTS

The OR and DR are generalized response systems which produce widespread, unconditioned changes in motor, autonomic, and central activities. Because of their generality, they have many response components in common, including EEG desynchronization, electrodermal resistance changes (GSR), and peripheral vasoconstriction. Curiously, these components, which do not differentiate the two systems, have been the most commonly employed in psychophysiological research, even when the research was explicitly concerned with orienting behavior. There are a number of other response components which probably do differentiate the systems, although the evidence for differentiation is not conclusive. Sokolov (1 963) claimed that the two systems could be distinguished by changes in cephalic vasomotor activity, with cephalic vasodilation indicating an OR and cephalic vasoconstriction a DR. Unfortunately,

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western investigators have not been able to replicate this finding unequivocally. Studies by R. C. Davis, Buchwald, and Frankmann (1955) and R. C. Davis and Buchwald (1957) offer some support but Royer’s work (e.g., 1966) suggests qualification of the findings; other studies (W. K. Berg, 1968; Raskin, Kotses, & Bever, 1969), as well as informal reports, indicate difficulty in replicating. There is some evidence that the systems may be more successfully distinguished by such central and autonomic components as hippocampal activity (Grastyhn, Karmos, Vereczkey, Martin, & Kellenyi, 1969, skin potential changes (Raskin er al., 1969), pupillary constriction or dilation (Sokolov, 1963), H R increase or decrease (Graham & Clifton, 1966), and by such motor responses as head turning, ear flicks and oculo-motor movements. The work in our laboratory has concentrated on HR change, which is a sensitive and reliable measure that can be easily recorded without disturbing the subject. Sokolov did not include direction of HR change among components that differentiate between an OR and a DR but Lacey (e-g., 1959) argued, on the basis of neurophysiological considerations and behavioral data, that HR deceleration occurs in situations of “stimulus intake” and H R acceleration occurs in situations of “stimulus rejection.” While Lacey was concerned with complex situations unlike the simple conditions in which orienting has been studied, Graham and Clifton (1966) hypothesized that, if Lacey’s reasoning were correct, HR deceleration should be a component of the OR, and HR acceleration a component of the DR. A review of the literature offered considerable support for the hypothesis, although the picture was complicated by some reports of a diphasic response of acceleration-deceleration in situations presumably appropriate for eliciting orienting. Graham and Clifton suggested that the initial, short latency, accelerative phase might be a consequence of a respiratory “startle” response and that this response might be due to the large onset transients produced by many methods of generating auditory signals. Subsequent work has provided additional support for the H R differentiation hypothesis. To distinguish an OR from a DR and thus to determine whether a component is differentiating, several criteria have been described by Sokolov. First, an OR is elicited by low-to-moderate intensity stimuli while a DR is elicited by high intensity stimuli. This is not an easily applied criterion, however, since there is no absolute definition of what constitutes “high” intensity, short of intensities producing tissue damage. While presence of a response difference as a function of stimulus intensity difference is evidence suggesting OR-DR differentiation, absence of a response difference may mean either that the particular

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type of response does not differentiate the systems or that the stimuli employed do not include stimuli both above and below the threshold for eliciting a DR. A second criterion is that the OR is elicited by change ir stimulation and thus habituates (diminishes) rapidly when the same stimulus is repeated. This criterion applies only to “non-signal” stimuli, i.e, stimuli which are not themselves reinforcing or associated with reinforcement. In contrast, a DR habituates slowly or may even be intensified by stimulus repetition. A third criterion also depends on the fact thal stimulus change is an effective stimulus for eliciting the OR. Since intensity decrease is as much a stimulus change as intensity increase, the response to offset of a sufficiently long-lasting stimulus should elicit an OR and could not elicit a DR. Consequently, if a response component is differentiating, onset and offset responses should be in the same direction when low-moderate intensity stimuli are used and should differ when high intensity stimuli are used. Differences in direction of HR change as a function of stimulus intensity have been shown in a number of studies (Graham & Clifton, 1966). The usual finding is HR deceleration with low intensity stimulation, and acceleration with high intensity stimuli such as painful shock and tones above 90 db. Between approximately 60 and 90 db, the diphasic acceleratory-deceleratory response has often been reported when rise time of tones is not controlled. Unpublished work from our laboratory (Hatton, Graham, & Berg, 1968) suggests that the initial acceleration of the diphasic response may be explained by onset characteristics.2 Using an electronic switch to control onset, even a 90 db re .0002 microbar tone elicited immediate deceleration when onset was gradual but elicited a diphasic response when the onset was sudden (300 ms versus osition and the animal in the rear half of its cage, it was no longer visible to S. The S was shown a duplicate set of animals and was told that each one “wanted” to be placed in the cage that contained his “friend” (i.e., a conspecific), and that he would be “unhappy” if mistakenly caged with an animal of a different species. Also available was a set of color photographs of each animal. After the first set of animals (R, = referent,) had been placed in the rear of each cage, S was told that the partitioning doors would shortly be closed and that as soon as they were, he would be given the second set of animals (R2) and would have to put them in their correct cages. It was suggested that he might do something with the pictures (S = symbol) now, while the doors were open and the R,s were visible, which would later assist him in making accurate R2 placements. In analogy with the Corsini et al. task, “production” was defined as placing each S in optical correspondence with its R, referent (e.g., at the base of its cage), and “mediation” as using the location of the Ss to guide the subsequent (with the R,s now nonvisible) placement of the corresponding R,s. Five trials were given, followed by either the first or both of two E-modeling trials, depending upon S’s performance; the first was wholly nonverbal, E silently demonstrating the above mentioned production-mediation sequence, whereas the second consisted of demonstration-plus-verbal-explanation. The data clearly showed that a number of these preschool children were quite capable of spontaneously and deliberately utilizing pictures as ikonic symbols to mediate their recall, given a facilitative, “cooperative” task setting; as would be expected, this capability was significantly age dependent across the 3 to 5% year age range. Thus, no fewer than 28 of the 50 S s produced and mediated perfectly on two successive trials during the initial five-trial sequence, and only 8 Ss never performed correctly, i.e., following two demonstrations by E. Of particular interest for the present discussion was the fact that putative production inefficiencies were about as common as outright production deficiencies on those trials where performance was not fully correct. The S might not touch the pictures at all, or merely finger or sort them (production deficiency). Alternatively, however, he might put only one S in correspondence with one R, (and later use it correctly to mediate that one R2 placement); he might put one S inside the cage, adjacent to its R1, so that it too was later screened from sight by the door; he might try to place S in correct position after, rather than before, the cage door was closed, and so on. We feel sure that at least some of these various behaviors reflected an intuition of the possible mediating function of the pictures coupled with some uncertainty or lack of skill (usually

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temporary) as to just how they should be made to perform that function. Our suspicion, then, is that production inefficiency may be a fairly frequent developmental precursor to efficient production, both where production is left to occur more or less spontaneously (our studies) and where it is experimentally induced at some ontogenetic remove from its normal age of spontaneous acquisition (the Kingsley and Hagen study). Assuming the production of a mnemonic mediator of proven effectiveness in older Ss, is there also a developmental period during which it fails to mediate (mediational deficiency)? There was certainly very little evidence for such periods in our initial five studies. Only one S in the aforementioned Ryan, Hegion, and Flavell study completely failed to utilize established S-R, contiguities to guide his subsequent placement of the R,s (mediational deficiency), and he only did so on one trial; a somewhat larger number of Ss made performance errors in attempting to utilize them (“rnediational inefficiency”). Despite the chronological immaturity of the S s in the Ryan et al. study, the predominant errors were clearly on the production side. Boat and Clifton (1968) also obtained clear-cut evidence of mediational abilities in preschool children (4-yearolds), using three paired-associate lists embodying a simple chaining paradigm (A-B, B-C, A-C). The evidence for mediational deficiencies is also meagre in studies by others, for instance, most of those cited earlier in this chapter. In fact, an investigator’s inference that his younger Ss are production-deficient is often based on data suggesting that they are not mediation-deficient. Suppose that it is found that E‘s provision of mediators to his older Ss does not significantly improve their performance, relative to that of a control group of the same age. The normal inference would be that children of this age produce and use these mediators spontaneously, and hence E‘s intervention was superfluous; these Ss would then be described as neither production-deficient nor mediation-deficient. Suppose that it is also found that provision of these mediators does significantly benefit the performance of the younger ss, again relative to that of their same-age controls. This finding-that they are not mediation-deficient - permits the inference that they are production-deficient, i.e., the poorer performance of the control Ss is attributable to the fact that they were not spontaneously producing the mediators. A recent study by Coates and Hartup (1969) is a case in point. Four-year-old and seven-year-old children observed a filmed model perform relatively novel and unexpected actions under one of three conditions: (1) induced verbalization (IV group), with S repeating aloud E’s standardized verbal description of each observed action as it occurred; (2) free verbalization (FV group), with S instructed to describe each action aloud in his own words; (3) passive observation (PO group), with no

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verbalization instructions given. For the older Ss, the recall levels were IV PO > FV, suggesting that the PO Ss had been spontaneously verbalizing the model’s actions covertly (IV PO), and perhaps thatrecall our earlier discussion of Murray’s ( 1967) findings -covert or semicovert self-codings may have been somewhat more effective mediators of recall than fully overt self-codings (PO > FV). For the younger Ss, the recall levels were IV > FV > PO, all differences highly significant, suggesting both the presence of a production deficiency (FV > PO and IV >PO) and the absence of a mediational deficiency; the IV > FV difference presumably reflects the greater precision (and hence, greater mnemonic-mediational potential) of E’s verses S’s verbal codings of the model’s actions. While it can thus be concluded from the existing evidence that mediational deficiency is a far less frequent and important determinant of nonmediated recall performance than is the production one, task conditions that might yield such a deficiency can at least be imagined. Our present guess is that the likelihood of finding a mediational deficiencyor, in analogy with the production case, a “mediational inefficiency” will be markedly dependent upon the precise conditions attending the production of that mediator. If one assumes, as we have been doing, that the production of mnemonic mediators is akin to attempts at problemsolving, then the provenance of that production might well affect its functional efficacy. As a general rule, E-induced mediator production ought to be less certain to have the expected mediational consequences than production of the spontaneous variety, since we can be surer in the latter case, as with self-generated problem-solving activities, that S really understands what he has done and sees its relevance to the recall test. “Marat-Sade” would not likely be an effective mediator for an 8year-old who is trying to remember “revolution,” “drama,” and “lunacy,” although he might humor you by producing it on command. Similarly, there probably exist mnemonic mediators which I could use but you could not, and conversely. This is, of course, not to imply that all induced production should be mediationally ineffective, even in those instances where S may have no conscious inkling of why he is being made to engage in it. Unlike the “Marat-Sade” example, enforced repetition of the names of familiar objects would likely have a positive effect on object recall for any S who knew their referents: the mediational link is maximally direct, preexperimentally overlearned, and should hence be virtually automatic for even very young Ss. It is noteworthy in this connection that the recall level of Kingsley and Hagen’s (1969) nursery school children actually did benefit from induced rehearsal, despite their aforementioned difficulties in complying with E’s rehearsal instructions.

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If it is really the case that spontaneous production, being intentional and goal-directed, almost always yields its expected quantum of mnemonicmediational effectiveness, and also that induced - even mindless - production may frequently do the same, it is not to be wondered at that mediational deficiencies are much more often sought than found. We need hardly add that if those which can be found really owe their existence solely to S’s incomprehension of the meaning and purpose of the mediational activity under study, that is, to the fact that S’s production is mindless, then mediational deficiency would have to be regarded as a theoretically trivial as well as empirically rare developmental datum. Assuming, then, that it is the transitions from nonproduction to production that comprise the significant developmental phenomena in this area, what additional conclusions can be tentatively made concerning these transitions? In analogy with most other developmental acquisitions (Flavell & Wohlwill, 1969), it can be surmised that the age of transition will be a joint function of both the nature of the mnemonic mediator considered and the nature of its eliciting task setting. There exists, as we have seen, a variety of possible mnemonic mediators. Neither common sense nor the existing evidence would lead one to believe that they are all acquired at the same mean age. For example, there are at least hints from Kingsley and Hagen’s (1969) study and from three of our own (Flavell et al., Daehler et al., and Moely et a/.) that genuine verbal rehearsal may be a later-developing mediational tactic than simple, unrepeated stimulus-naming. In turn, spontaneous and deliberate efforts at finding conceptual and associative linkages among items to be recalled probably emerges later in ontogenesis than does verbal rehearsal (Jensen & Rohwer, 1965; Martin, 1967; Moely et al., 1969). And finally, the results of the Ryan et al. study suggest that the capability for some forms of ikonic mediation may appear very early, prior to verbal rehearsal and possibly in rough synchrony with simple stimulus-naming. The analogy with problem solving comes once again to mind: some mnemonic-mediational strategies (problem-solving strategies) require more cognitive maturity than others, and their acquisitions are correspondingly ordered in ontogenesis. For any one of these mediators, however, the age of transition from nonproduction to production should also depend very heavily upon the specifics of the task conditions under which it is assessed. One class of specifics includes the nature of Es behavior toward S. H e may do nothing in the way of prompting S’s production; he may provide weak and indirect suggestion; or he may provide explicit instruction, direction, or modeling. Such variations in Es behavior have already been shown to have very powerful effects on mediator production and utilization in the

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Keeney et al., Corsini et al., and Moely et al. studies; similarly, Es modeling of the S-R1 and S-R, linkages in the recently completed Ryan et al. investigation was for 14 Ss a necessary but sufficient condition for production (recall that it was not sufficient for 9 others, however). An input from E that is sufficient to elicit production will not necessarily be sufficient to sustain it, as the post-input behavior of the nonproducers in the Keeney et al. study demonstrates; similar findings have also been reported by Milgram (1967, 1968b). The physical aspects of the task setting are also likely to be important variables. The gap in age for ikonicmediator production in the Ryan et al. versus Corsini et al. investigations must have been largely explainable on this basis (e.g., the use of animals versus abstract geometrical forms, of photographs versus paper replicas, etc.). Subtle differences in both mediational activity and task conditions may have been responsible for the following putative developmental sequence, constructed from the Flavell et al., Keeney et al, and Moely et al. data: (1) verbalization of stimulus names during the study periods of the Moely et al. task (very frequent among kindergarten Ss); (2) verbalization of stimulus names during the brief delay periods between stimulus offset and recall testing in the Flavell et al. and Keeney et al. task (infrequent prior to Grades 1-2); (3) self-testing, i.e., deliberately averting one’s head from the stimuli during the study periods of the Moely et al. procedure and verbalizing their names, presumably for purposes of rehearsal and/or monitoring of progress (infrequent prior to Grade 3). Consider first the sequence (1) + (2). In the Moely et al. task, the object pictures were continuously visible for a full 2 minutes on each trial, whereas they were of course out of the child’s sight during the delay periods of the Flavell et al. and Keeney et al. procedure. Whether one prefers to characterize this as a difference in the type of mediator used (stimulus-naming versus rehearsal) or a difference in task conditions (stimuli present versus absent), it is plausible that it could help account for the observed sequence. Moreover, the Ss in the Moely et al. experiment had to indicate their recall of the objects by naming them, not merely by pointing to them in sequence as was the case in the other two studies. This difference, more clearly of the taskconditions variety, may also have played a causal role, i.e., with naming during recall “priming” naming during stimulus presentation or something of the sort. Recall that having to name the stimuli at stimulus presentation and at test in the Flavell et al. study (supplementary series) increased delay-period rehearsal in the kindergarten group. (3), one again takes his choice between As for the sequence (2) mediator and task variables. Delay-period rehearsal is a subject-pro-

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duced activity made in response to an experimenter-produced physical isolation from the objects whose names are rehearsed. In contrast, selftesting is a subject-produced activity made in response to a subject-produced isolation (averting the eyes, etc.). Thus, the first-grade producer in the Keeney et al. study rehearsed despite the absence of the stimuli; in contrast, the third- and fifth-grade self-testers in the Moely et al. study did the same despite their presence, a much more subtle and maturelooking mnemonic tactic but, like both (2) and ( l ) , no less a form of “verbal mediation.” Although some suggestions have just been made about factors that may affect the developmental timing of nonproduction-production transitions, the basic fact that such transitions exist is not thereby fully explained. While the author is frankly uncertain as to exactly what a “full explanation” of any cognitive-developmental phenomenon ought in principle to look like (an uncertainty probably shared by many other developmental psychologists), he is at least sure that none is yet at hand regarding production deficiency and its remediation. For whatever it may be worth, our current belief is that these transitions may reflect underlying cognitive-developmental changes of two types, specific and general. The specific ones would refer to the particular cognitive activities which underlie the use of particular mnemonic mediators, each form of mediational activity being assumed to comprise its own unique constellation of skills. In the case of verbal rehearsal, for example, we could suppose that the growing child increasingly overlearns verbal-label responses to object stimuli, becomes increasingly skillful at rapid, subovert articulation of a string of labels, becomes better attuned to the sequencing and recycling (starting again at the first word) “rules” of repeated rehearsal, and the like. As these component skills mature, verbal rehearsal becomes a more serviceable and hence more readily elicitable response pattern in a variety of appropriate situations, including those in which it could serve to mediate recall. One supposes further that, for this mediator especially, formal schooling with its heavy emphasis on verbal skills may play a powerful acquisition-fostering role. The general change might consist of an increasing propensity, both in recall tasks and in many others which have a similar means-to-ends structure, to search the repertoire for activities to perform now, the performance of which has no immediate relevance but will facilitate some other activity subsequently (in this case, recall). This propensity - we have recently come to term it “planfulness” or “planning ability” -is not the exclusive skill-component property of any one specific mnemonic mediator; rather, it could be viewed as a kind of cognitive “executive

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routine” which tells S that the search for a mnemonic mediator is in order when faced with a recall task. Thus, an explanation of some instances of nonproduction - nonrehearsal, say - might simply be s’s inability to rehearse easily and efficiently (a specific factor). An explanation of other (or the same) instances, however, might be S’s failure to keep the goal continuously in mind, and to recognize fully that he ought to be doing something of a planful nature now to make its subsequent attainment more probable (a general factor). Actually, the transition from nonproduction to production for any given mediator would probably entail an interplay or interaction between both kinds of developmental change. It is perhaps easiest to imagine such an interaction as proceeding from the general to the specific: with increasing cognitive maturity, the child is more and more likely to think of acting planfully in recall situations, and thus to look for some mnemonic; if, say, skill at verbal rehearsal is also sufficiently advanced at that point in his ontogenesis (and if, of course, this recall task lends itself to verbal-rehearsal management), the child will then likely find and use that particular mnemonic. A flow in the opposite direction is also conceivable, however: with the child sufficiently mature for verbal rehearsal to have a low threshold as a response in this particular situation (given that the stimuli to be recalled have familiar, one-word labels, etc.), rehearsal may occur initially in an almost reflexive fashion; its usefulness as a mediator may then become only gradually apparent, perhaps as a consequence of feedback as to its effects on recall. It may even be that the sense of planfulness of which we have been speaking develops in part as a consequence of the maturation and repeated (initially nonplanful) utilization of potentially mediative actions, a notion reminiscent of Mandler’s ( 1962) “association-to-structure” conception and of Piaget’s (1 952) theory of the early genesis of intentionality. Although we of course cannot be sure, it was our impression that the microgenesis of ikonic mediation in the Ryan et al. task went from a sense of planfulness to picture-utilization in some S s and from picture-utilization to a sense of planfulness in others. Thus, one child might simply stare at the pictures, apparently aware that he ought to do something with them to assist subsequent R1-R2matchings, and then suddenly intuit the whole solution. In contrast, another might idly bring the pictures up next to their animal referents on one or more trials (a prepotent, high-probability response to these particular task materials for young children, we think, even without a recall set) and, seemingly, induce a means-to-ends, planning set in the course of going from S to R2.In summary, the hypothesis is that many of the observed developmental changes in children’s behavior in recall settings may be joint consequences of an increasing sensitivity

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to the need for planful and preparatory activity, to be carried out prior to the recall test, coupled with an increasingly varied repertoire of serviceable mediators from which to select for this purpose.

c. IMPLICATIONS

FOR

FURTHER RESEARCH

Many of the conclusions we have proffered concerning mnemonic mediation and its development are very speculative, perhaps excessively so. There is, therefore, an obvious need for more and better research evidence to confirm them or, where incorrect, to suggest alternatives. Rather than try to sketch out specific research designs for specific points of interpretative insecurity, however, we shall conclude by simply offering two general recommendations for future research. Although they are closely related, one is methodological and the other substantive. The methodological suggestion is to investigate the occurrence-nonoccurrence and the structure of ordinarily covert mediational activities by rendering them observable, insofar as present research technology, the investigator’s imagination, and the nature of the activity studied will permit. While it is true that inferences about mediational activity can and often have been made from indirect evidence (e.g., from S’s recall performance), direct, observational data are surely better when and where they can be had. We believe that our conclusions regarding production versus mediational deficiencies are far more secure for the fact that we attempted to observe rather than infer the presence-absence of phenomena such as rehearsal (Flavell et ul., Keeney et ul., Daehler et ul.), ikonic mediation (Corsini et af.,Ryan et ul.), and clustering (Moely er ul.), Furthermore, whereas direct, observational methods may be merely preferable for a diagnosis of production versus nonproduction, they are probably indispensable if one wants to learn anything about the structure and developmental status of whatever mediational activity was produced. Ikonic mediation is the best illustration at hand: the encoding and decoding activities elicited by the Corsini et al. and Ryan et al. tasks are fully externalized and must by their very nature proceed at a pace easily monitored by an observer (one picture placed next to one animal, then another, etc.). As such, the investigator can detect and classify S’s errors and false steps (production and mediational inefficiencies), and from these hopefully make good inferences about the psychological structure of this simple-looking form of symbolic-mediational activity. The substantive suggestion is as follows. The mnemonic-mediational behaviors we have been studying bear a close relationship to a real-life activity to which many, many childhood hours are devoted, namely, studying. Very little is known concerning just how children of different

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ages set about trying to commit information of various sorts to memory. The research described in this paper suggests that there would be significant developmental changes in children’s “operant studying behavior,” that is, in what they do when left alone with material they are to learn, e.g., when doing homework. In keeping with the methodological point made above, ways might be found to gain observational access to this private-looking behavioral preserve. How do children of different ages spontaneously order and organize data which are to be learned? How do they assess their own progress in mastering them (recall the curious selftesting procedures devised by the older children in the Moely et al. experiment)? Answers to such questions might have important educational as well as scientific theoretical uses. We have yet to appraise thoroughly the variables for teaching effective mediators, but the practical implications of this method are large. There is no reason why schoolteachers of future generations should not show students ways of learning materials that will result in their high recall. At present, students are given materials for learning and are left to their own memory devices. How much better it would be if an instructor told the students about proved mnemonic devices and saw that they used them in systematic ways [Adams, 1967, p. 1341.

IV. Summary This paper reports and interprets recent studies dealing with the development of mnemonic-mediational skills in children, e.g., verbal rehearsal. The following were among the major conclusions suggested by the available evidence. ( 1) There are many different types of mnemonic-mediational activities, even within a single system of symbolic representation such as the verbal one. Mnemonic mediation is best conceived as a planful, instrumental, cognitive act, akin to problem-solving behavior. (2) Descriptively, the developmental course of acquisition of any given mnemonic mediator typically consists of an age-dependent increase in the likelihood of its spontaneous occurrence in appropriate recall situations (production deficiency + production), rather than an age-dependent increase in the likelihood that, given its occurrence, it will mediate recall effectively (mediational deficiency + mediation). Mediator production is not an all or nothing affair, however; developmental intermediaries (“production inefficiencies”) between nonproduction and efficient production are probably the rule rather than the exception. (3) The average age of transition from nonproduction to production varies both with the particular mediator studied and with the particular

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task conditions (stimuli used, testing procedure, E's instructions, etc.) which elicit it. (4) The passage from nonproduction to production of any mnemonic mediator may be the joint resultant of cognitive-developmental changes at two levels: (a) a general, mediator-nonspecific ontogenetic movement toward greater planfulness (tendency to look for present means to the attainment of future ends): (b) the gradual acquisition and perfection of the specific cognitive skills which underlie, or constitute the components of, specific mnemonic -mediational activities.

ACKNOWLEDGMENTS The author is grateful to Marilyn Rea for her assistance in gathering and processing data, to Mervyn 0. Bergman for his technical assistance, to the personnel of the schools from which the Ss were obtained, and to the many students and colleagues who made invaluable contributions to the research project.

REFERENCES Adams, J . A. Human memory. New York: McGraw-Hill, 1967. Bernbach, H. A. The effect of labels on short-term memory for colors with nursery school children. Psychonornic Science, 1967,7, 149- 150. Boat, B. M., & Clifton, C., Jr. Verbal mediation in four-year-old children. Child Development, 1968,39,505-514. Bruner, J . S., Olver, R. R., & Greenfield, P. M. (with others). Studies in cognitive growth. New York: Wiley, 1966. Coates, B., & Hartup, W. W. Age and verbalization in observational learning. Developmental Psychology, 1969, 1, 556-562. Corsini, D. A., Pick, A. D., & Flavell, J. H. Production of nonverbal mediators in young children. Child Development, 1968, 39,53-58. Daehler, M. W., Horowitz, A. B., Wynns, F. C., & Flavell, J. H. Verbal and nonverbal rehearsal in children's recall. Child Development, 1969, 40, 443-452. Flavell, J . H., Beach, D. H., & Chinsky, J. M. Spontaneous verbal rehearsal in a memory task as a function of age. Child Development. 1966,37,283-299. Flavell, J. H., & Wohlwill, J. F. Formal and functional aspects of cognitive development. In D. Elkind & J. H. Flavell (Eds.), Studies in cognitive development: Essays in honor ofJean Piaget. London & New York: Oxford University Press, 1969. Pp. 67-120. Gratch, G. The use of private speech by Head Start and middle class preschoolers: An investigation of the mediating function of language in a non-linguistic memory task. Paper presented at the meeting of the Southwestern Psychological Association, Arlington, Texas, April, 1966. Hagen, J. W., & Kingsley, P. R. Developmental studies of verbal labelling effects on memory. Paper presented at the meeting of the Midwestern Psychological Association, Chicago, May 1968. (a)

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Hagen, J. W., & Kingsley, P. R. Labelling effects in short-term memory. Child Development, 1968.39, 113-121. (b) Jensen, A. R. Rote learning in retarded adults and normal children. American Journal of Mental Deficiency, 1965, 69, 828-834. Jensen, A. R., & Rohwer, W. D., Jr. The effect of verbal mediation on the learning and retention of paired associates by retarded adults. American Journal of Mental D e j ciency, 1963, 68, 80-84. Jensen, A. R., & Rohwer, W. D.. Jr. Syntactic mediation of serial and paired-associate learning as a function of age. Child Development. 1965,36,601-608. Keeney, T. J., Cannizzo, S . R., & Flavell, J . H. Spontaneous and induced verbal rehearsal in a recall task. Child Development, 1967,38,953-966. Kendler, H . H., & Kendler, T. S . Vertical and horizontal processes in problem solving. Psychologicul Review, 1962, 69, 1- 16. Kendler, T. S. Development of mediating responses in children. In J. C. Wright & J. Kagan (Eds.), Basic cognitive processes in children. Monographs ofthe Societyfor Research in Child Development, 1963, 28(2), 33-52. Kingsley, P. R., & Hagen, J. W. Induced versus spontaneous rehearsal in short-term memory in nursery school children. Developmental Psychology, 1969,1,40-46. Kuhlman, C. K. Visual imagery in children. Unpublished doctoral dissertation, Radcliffe College. 1960. Luria, A. R. The genesis of voluntary movements. In N. O’Connor (Ed.), Recent Soviet psychology. New York: Macrnillan (Pergamon), 1961. Pp. 165-185. Maccoby, E. E. Developmental psychology. Annual Review of Psychology, 1964, 15, 203-250. Mandler, G. From association to structure. Psychological Review, 1962, 69,415-426. Martin, C. J. Associative learning strategies employed by deaf, blind, retarded and normal children. Final Report, 1967, Office of Education Grant No. 5-0405-4-1 1-3. Milgram, N. A. Retention of mediation set in paired-associate learning of normal children and retardates. Journal of Experimental Child Psychology, 1967,5, 341 -349. Milgram, N. A. The effect of verbal mediation in paired-associate learning in trainable retardates. American Journal of Mental Dejciency, 1968, 72, 5 18-524. (a) Milgram, N . A. The effects of MA and IQ on verbal mediation in paired associate learning. Journal ofGenetic Psychology, 1968, 113, 129-143. (b) Moely, B. E. Children’s retention of conceptually related items under varying presentation and recall conditions. Unpublished doctoral dissertation, University of Minnesota, 1968. Moely, B. E., Olson, F. A., Halwes, T. G., & Flavell, J. H. Production deficiency in young children’s clustered recall. Developmental Psychology, 1969, 1, 26-34. Murray, D. J. Overt versus covert rehearsal in short-term memory. Psychonomic Science, 1967, 7, 363-364. Piaget. J. The origins of intelligence in children. New York: International Universities Press, 1952. Posner, M. I . Characteristics of visual and kinesthetic memory codes. Journal of Experimental Psychology, 1967,75, 103-107. Ranken, H . B. Language and thinking: Positive and negative effects of learning. Science, 1963,141,48-50. Reese, H. W. Verbal mediation as a function of age level. Psychological Bulletin, 1962,59, 502- 5 09. Rosenbaum, M. E. The effect of verbalization of correct responses by performers and observers on retention. Child Development, 1967,38, 614-622.

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Ryan, S. M., Hegion, A. G . , and Flavell, J. H. Nonverbal mnemonic mediation in preschool children. Child Development, 1970, 40, in press. Silverman. I. W. Effect of verbalization on reversal shifts in children: Additional data. Journal of Experimental Child Psychology, 1966, 4, 1-8. Silverman, I. W., & Craig, J . G . The roles of encoding practice and enforced decoding in verbal mediation: A developmental study. Paper presented at the meeting of the Society for Research in Child Development, New York, March 1967. Smith, R. K.. & Noble. C. E. Effects of a mnemonic technique applied to verbal learning and memory. Percepfual and Motor Skills, 1965.21. 123-134. Underwood, B. J. The representativeness of rote verbal learning. In A. W. Melton (Ed.), Categories of human learning. New York: Academic Press, 1964. Pp. 47-78. Vygotsky, L. S. Thought and Language. Cambridge, Mass.: M.I.T. Press and New York: Wiley, 1962.

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DEVELOPMENT AND CHOICE BEHAVIOR IN PROBABILISTIC AND PROBLEM-SOLVING TASKS

L . R . Goulet' and Kathryn S. Goodwin WEST VIRGINIA UNIVERSITY

I . INTRODUCTION

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I1. PROBABILITY LEARNING

A . DEFINITIONS AND METHODS .......................... B EARLY RESEARCH ...................................... C . DESCRIPTIVE DEVELOPMENTAL CHANGES IN PROBABILITY LEARNING ............................... D VARIABLES INFLUENCING PROBABILITY LEARNING: TASK VARIABLES ......................................... E TRANSFER O F TRAINING ................................ F . THEORETICAL INTERPRETATIONS O F AGECHANGES IN PROBABILITY LEARNING .................. G INCENTIVE ............................................... H COMMUNALITY OF RESPONSE PATTERNS ACROSS TASKS AND SUBJECTS ....................................

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GUESSING BEHAVIOR .................................. ALTERNATION BEHAVIOR .............................. STUDIES O F T H E DEVELOPMENT O F THE PROBABILITY CONCEPT ............................................... 248

OVERVIEW

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REFERENCES

'Now at the University of Illinois. Urbana . 213

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I. Introduction The study of children’s performance in probability-learning tasks is of recent vintage but nevertheless occupies much current interest. This interest apparently stems from the rather striking developmental changes that have been observed when these tasks are used, and from the current view that these tasks represent an approach to the study of problemsolving and, as such, have utility in the assessment of developmental changes in problem-solving strategies. Furthermore, probability-learning paradigms have more-than-apparent similarity to discrimination learning tasks, the multiple-choice tasks used to study response preferences, gambling behavior, etc. In addition, there is a considerable body of research and theory related to other similar problems, e.g., the development of the concept of probability and “spontaneous alternation” behavior, most of which has just recently been seen as related to the probability learning literature. The present purpose is to provide a general review of the research related to probability learning and similar tasks, with an emphasis on data collected using children as subjects. More specifically, an attempt will be made to provide some degree of integration of the literature related to developmental changes in choice behavior. There are recent reviews focusing on response preferences (Tune, 1964a, 1964b), spontaneous alternation behavior (Dember, 1961; Schultz, 1964), and probability learning (e.g., Atkinson, Bower, & Crothers, 1965; Estes, 1964) in young adult subjects. This research will be cited only as it relates to the focus of this paper. In addition, Gerjuoy and Winters ( 1968) have summarized the literature related to response preferences and choice behavior of retardates; the work cited therein will also be discussed only as it assists in the elaboration of the present data.

11. Probability Learning A. DEFINITION AND METHODS

1. .Nature and Utility of the Tasks The difficulty in specifying just what tasks or experimental situations should be included in a review of probability learning is made evident by Estes (1964), who noted that “probability learning is easier to identify than to define [p. 891.” However, probability learning like many familiar types of learning classifies as a “type” because of the communality of problems and procedures around which research activity is centered.

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Although it is rather easy to distinguish the studies that are relevant to this problem, it can be noted just how close the study of probability learning is to other areas of interest. In fact, the oldest variant of the probability-learning designs was devised by Humphreys ( 1 939) as a verbal analogue to Pavlovian conditioning (Atkinson et af., 1965). Moreover, in some instances, probability learning seems to be simply a special case of discrimination learning. If one considers a simple discrimination problem with partial reinforcement of a position discrimination, one finds exactly the same task often used in probability learning. The research in probability learning is generally concerned with two types of behavior. Some research is designed to assess the subject’s understanding of the nature of probability events (e.g., Yost, Siegel, & Andrews, 1962), while other research involves the use of the probability-learning tasks for evaluating problem-solving behavior (e.g., Weir, 1964). Although it is of interest to see how concepts of probability are developed, it appears more likely that the study of problem solving will be more productive for learning theory in general. As Brunswik (1939, 1943) has argued, the probability-learning paradigm, where partial reinforcement is the rule, is more representative of everyday life than the classical learning situations which involve 100% reinforcement. Typically, means to a goal are rarely absolutely reliable or absolutely wrong. The tasks most commonly used in the study of probability learning have been those where subjects are reinforced on some specified (in most cases experimenter-determined) partial reinforcement schedule for choosing or responding to one or a combination of stimuli from a finite array. The two-choice problem best exemplifies the nature of the task. In this case, subjects are instructed to predict which of the two events will occur on each of a series of trials. The schedule of partial reinforcement is typically determined such that one of the available stimuli is presented at a level considerably above chance but below unity and the other stimulus is presented on the remaining trials. For example, in a 70:30 task the fixed proportions of occurrence of two events over a block of trials are 70 and 30%, respectively. However, even though the events are presented in fixed proportions over the total number of trials, each occurs in a random (nonpredictable) sequence, limited only by the partial reinforcement schedule. There are a number of variations of the task and these will be specified in detail at a later point in the paper. However, it may be fruitful to specify just what can be “learned” in a task of this nature. First, subjects can obtain information regarding the percentage of occurrence of each event over the block of trials. Second, subjects can “learn” or deduce the optimum strategy for maximizing the number of “hits” (correct predictions). In the example cited above, the number of hits can be maxi-

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mized by predicting the most frequently occurring event on every trial. Third, subjects can “learn” which strategies do not maximize hits; i.e., nonefficient (incorrect) strategies can be inhibited. The last statement may be merely rephrasing what was said above, but its inclusion immediately makes apparent the possibility of the reinforcement and maintenance of “superstitious” behavior in tasks of a probabilistic nature. To the extent that subjects are reinforced (albeit on a partial-reinforcement schedule) for predicting the least frequently reinforced event, or for sequential behavior involving response patterns, the probability of occurrence of these behaviors can increase and be maintained. Each of the above problems is discussed in detail below. Why are these tasks used in developmental research? (a) Perhaps the most apparent reason is that performance measures can be obtained from a wide variety of subjects, i.e., the ability to perform on these tasks is, for the most part, independent of language skills, intellectual ability, etc. (b) Furthermore, the data obtained seldom suffer from “ceiling” or “floor” effects, which prevent statistical comparisons when tasks are too easy or too difficult for some or all of the subjects tested. (c) A wide variety of independent variables can be manipulated without modifying the essential nature of the task. For example, performance comparisons have been made under varying levels of incentives, both material and social, and sociopsychological variables such as social class (Odom, 1967; Rosenhan, 1966), sex of the experimenter (Odom, 1966), social deprivation (e.g., Lewis, 1965), reward and/or punishment (Das & Panda, 1963; Gruen & Weir, 1964; Offenbach, 1964), have been used. (d) Finally, the behavior manifested in tasks of this nature has been considered to reflect strategies of problem-solving characteristic of the age groups being studied. Indeed, much of the recent research has been oriented to the discovery of such strategies. The tasks involving choice behavior provide the opportunity for subjects to utilize widely variable “strategies” under identical conditions. Such strategies may be those which subjects bring to the laboratory, i.e., preexperimental strategies which are a function of maturational and/or experiential factors. Such strategies should be reflected in the performance in the early stages of practice. In contrast, asymptotic performance, i.e., behavior manifested in the later stages of practice, after which the subjects’ responding has reached a steady state, at least theoretically reflects a strategy which has been adopted as a result of the reinforcement of certain patterns of behavior and/or nonreinforcement of other patterns. The change and rate of change in performance from the early stages to later stages of practice, therefore, reflect the systematic elimination of inefficient strategies and/or acquisition of efficient strategies.

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2 . Methods In a manner similar to discrimination learning (e.g., Lipsitt, 1961; Spiker & Lubker, 1965), the tasks may be presented according to simultaneous or successive methods. With the simultaneous method of presentation, each of the stimuli is available to the subjects for selection on every trial; in the successive method only a warning signal or warning stimulus is presented and the subject must designate which stimulus of the array is to appear following his response. This distinction is important because, in addition to differences in method of presentation, another variable, information feedback, is typically confounded. That is, the successive method conveys information as to the reinforced stimulus on every trial whether or not the subjects choose or predict correctly. The typical procedure of simultaneous presentation conveys information regarding the correct response only if the subject chooses correctly or if the experimental procedure is such that the reinforced stimulus is identified whether or not the correct response is chosen. Providing information feedback on every trial has been called a noncontingent information feedback because such feedback is not dependent on the subject’s response. Similarly, contingent information feedback provides information regarding the correct response or incorrect response depending on whether the subject chooses correctly on that trial. As mentioned above, the use of the simultaneous method of presentation permits the experimenter’s choice of the use of either a contingent or noncontingent procedure of information feedback, but only the noncontingent procedure is possible when the successive method of presentation is used (e.g., Offenbach, 1965). There have been three basic types of reinforcement schedules used in probabilistic tasks, each of which may vary along the continuum from partial to continuous reinforcement. One of the schedules is that used for the typical probability-learning task. The basic requisite with this schedule is that the correct stimulus on each trial is determined by the experimenter prior to the initiation of practice within the limitations of the chosen level of reinforcement. In this case, the subject is reinforced on a specific trial only if he chooses the stimulus designated “correct” on that trial. We may call this type of schedule a trial-defined schedule. A second type of reinforcement schedule has been used by Stevenson (Stevenson & Hoving, 1964; Stevenson & Weir, 1959; Stevenson & Zigler, 1958), Weir (Weir, 1967, 1968; Weir & Gruen, 1965), Odom (1966, 1967), and others. This schedule, which may be called a response-defined schedule, involves reinforcing a fixed percentage (e.g., 66%) of the subject’s responses to a particular stimulus, independently of the trial on which they are made. However, the trial on which the sub-

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jects can be reinforced for choosing a particular stimulus is not determined prior to practice as it is with the trial-defined schedule. It should be mentioned that the use of a response-defined schedule precludes the use of the noncontingent information feedback procedure. A third type of schedule may be designated as a “random” reinforcement schedule, where the specific trials on which the subject is to be reinforced are predetermined and reinforcement is provided independently of the stimulus to which he responds (e.g., Goulet & Barclay, 1967; Jeffrey & Cohen, 1965; Rieber, 1966). It is apparent that there is no optimal strategy of responding when random reinforcement schedules are used. In fact, the number of times reinforcement is provided over a block of trials is invariant no matter which strategies, response patterns, etc., are used. However, one of the intriguing aspects of random reinforcement is that it can be used to reinforce-and maintain-the strategies that subjects bring to the laboratory. There are a number of other ways in which the tasks for the study of choice behavior can vary. As has already been mentioned, the number of stimuli can vary from two to many, although two- and three-choice tasks have been most commonly used. In addition, both response-defined and trial-defined schedules can be modified such that responses to one or more of the stimuli are reinforced. For example, with a twochoice task, either 75:25 or 75:O schedules of partial reinforcement could be used. In other words, the level of reinforcement for each stimulus is experimenter-determined, can be programmed independently for each of the stimuli in the task, and can take values ranging from 100 to 0%. As is apparent, whenever the reinforcement is 100:0,the distinction between a discrimination-learning task and probability-learning task (using a trial-defined or response-defined schedule) disappears. At the other extreme, when the schedule is 100: 100, there is considerable disparity between the two schedules and the discrimination-learning task; however, the schedules are now identical to one generated using a 100% random reinforcement schedule. B. EARLYRESEARCH

The widely diverse group of studies related to the behavior of children in probabilistic tasks has not been systematically reviewed. As mentioned above, one of the purposes of the present paper is to attempt such a review of both the results and the general interpretations proffered for the obtained effects of age, schedule, task, etc. It is also of interest to highlight some of the reasons for the initiation of the first studies. Messick and Solley (1957) were interested in a number of general problems, whether children’s (CA = 3-8 years) behavior in a two-choice

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task (successive procedure, noncontingent information feedback, trialdefined schedule) was best characterized by “maximizing” or “probability matching,” whether the subjects’ choice behavior in a 60:40 schedule deviated systematically from that expected by chance (choosing the two stimuli with equal frequencies), and whether incentive (candy) reinforcement for correct choices affected choice behavior. Unfortunately, the samples used were extremely small (N = 1-3) and each of the children was tested under all of the permutations of schedule, incentive, etc., used in the study. The results indicated a trend toward probability matching (choosing the stimuli at the level each is reinforced) under 100:0, 90: 10, 75:25, and 60:40 schedules, independent of age. Furthermore, the probability matching under the 60:40 schedule suggested that even 3- and 4-year-olds could discriminate between a 60:40 and a 50:50 task. When a material incentive was provided for correct predictions in a 75:25 task, the older subjects (CA = 7-8 years) maximized, the youngest subjects’ (CA = 3-4 years) behavior was still characterized by probability matching, and the terminal level of performance of the 5-year-olds reached an asymptote intermediate to maximizing and matching. In another early study, Stevenson and Zigler (1958), using a threechoice task (simultaneous procedure, contingent information feedback, response-defined schedule), found that the asymptotic performance of nursery school children varied directly with the schedule of reinforcement (100:0:0, 66:0:0, 33:0:0), the asymptotes after 80 trials being approximately .90, .80, and 3 0 for the three schedules, respectively. In contrast, the asymptotic performance of groups of MA-matched retardates (mean CA = 12.8 years) on the same task and schedules approximated .90, .90, and .65, respectively. The normal-retardate differences were attributed to differential expectancies of continuous reinforcement between the groups of children. That is, normal children were assumed to have learned through everyday experiences to expect a high degree of success in problem-solving tasks. Such an expectancy would not lead to maximizing behavior with a partial reinforcement schedule since the children would search for a sequence or pattern of responses which would yield continuous reinforcement. In Experiment 111, Stevenson and Zigler (1958) tested the hypothesis that the subjective expectancies of success for the children could be modified by pretraining involving either partial or continuous reinforcement. The three pretraining tasks were games structured to yield either partial (33%) or continuous (100%)reinforcement for different groups of nursery school children (mean CA = 5.9 years). Subsequent performance on the 66:O:O task was better following pretraining on the partial schedule than following pretraining on the continuous schedule.

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The absence of a no-pretraining control group made it impossible to determine whether the differences in performance as a function of pretraining were due to interfering effects of pretraining on the continuous reinforcement schedule, facilitative effects of pretrainhg on the partial reinforcement schedule, or both. However, it is possible to compare the performance of the subjects from Experiment I (who had no pretraining) to those from Experiment 111. These data are presented in Fig. 1. As can be seen in Fig. 1, pretraining interfered with performance on the early trials; however, in line with Stevenson and Zigler’s hypotheses, subjects pretrained on a partial reinforcement schedule had a higher terminal level of performance than the “control” group, and the performance of subjects pretrained on a continuous reinforcement schedule was depressed below that for the control group throughout practice. The initial inhibitory effects are unexplained. An experiment by Stevenson and Weir (1 959) provided further evidence that performance varies with the level of success that subjects will accept in the task. Reasoning that older children would seek a solution that would provide them with continuous reinforcement, Stevenson and Weir compared subjects (CA = 3, 5,7, and 9 years) on 100:0:0,66:0:0, and 33:O:O tasks. The number of choices of the reinforced stimulus varied inversely with age on each of the three schedules. However, the age-differences were attributable primarily to the greater number of 98 7 -

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Fig. 1 . Mean number of correct responses in blocks of 10 trials for the control, partial reidorcement (33%). and continuous reinforcement (100%) groups. [Adapted from Stevenson and Zigler (1958) wirh the permission of the authors and the American Psychological Association.]

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choices of the reinforced stimulus by the younger subjects on the early trials. In other words, a pronounced trend toward maximizing was apparent in the 3-year-olds even in the first block of 10 trials. This was true for each of the schedules of reinforcement. In addition, although performance varied directly with the reinforcement schedule in all agegroups, the performance differences among schedules increased with age. The early research and the obtained results highlight many of the theoretical issues and problems related to development that may be investigated with probability-learning tasks. Stevenson and Zigler (1958) and Stevenson and Weir ( 1 959) have suggested that the greater trend toward maximizing found in younger subjects and in retarded subjects is a function of experiential rather than maturational factors related to development. In this regard, comparisons of performance in probability learning among children of different ages may be considered as studies of transfer of training where performance on the task is a function of differential experience with expectancies of success in problem-solving situations. This interpretation points to the importance of transfer studies where the subjects’ subjective expectancies of success are experimentally manipulated by laboratory practice on tasks of a probabilistic nature. This work is discussed in detail in the section on transfer of training. Alternatively, the age differences found may be attributable to systematic, developmental changes in characteristic patterns of choice behavior. These characteristic patterns of behavior may indeed reflect “strategies” of problem-solving based on the subjects’ hypothesis that the task has a solution; i.e., that a certain “to be discovered” pattern of responding will yield continuous reinforcement. However, it is possible that performance of very young children e.g., 3-year-olds, is not a function of strategies per se, but rather a pattern of responding based on reinforcement. In other words, the choice behavior of very young children may be characterized by perseveration to a reinforced stimulus. This hypothesis is consonant with the data obtained by Stevenson and Weir (1959) since only one stimulus was reinforced in their tasks; i.e., either 100:0:0, 66:0:0,or 33:O:O schedules were used. Older subjects may systematically formulate, test, and reject hypotheses (based on the assumption that the task can be solved). Maximizing behavior will not be found if the strategies or hypotheses formulated deviate from perseveration. This, of course, would account for the trend toward decreased maximizing behavior with increasing age. This trend was also found with two-choice tasks by Jones and Liverant (1960). They used 70:30 and 90: 10 schedules (simultaneous procedure, contingent information feedback, trial-defined schedule) and found that the performance of young children (CA = 4-6 years) was better

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than that of older children (CA = 9-10 years). These data contradict those of Messick and Solley (1957). Apparently, the latter data are biased because of the small number of subjects, the multiple conditions under which each subject was tested, or both. C. DESCRIPTIVE DEVELOPMENTAL CHANGES IN PROBABILITY LEARNING

Much interest has been generated by a recent paper by Weir (1964). He consolidated the data from a number of previous studies (Gruen & Weir, 1964; Stevenson & Weir, 1959, 1963) in which subjects (CA = 3-20 years) had performed on the same task, apparatus, procedure, instructions, etc. The subjects were tested for 80 trials under 66:O:O or 33:O:O schedules of partial reinforcement (simultaneous procedure, contingent information feedback, response-defined schedule). When the percentage of choices of the reinforced stimulus during the last block of 20 trials was plotted as a function of age, a U-function was obtained; i.e., the 3-year-olds, 5-year-olds, and college students showed similar terminal levels of performance, but the performance of 7-, 9-, 1 1-, and 15-yearolds was depressed below that of the others. Similar functions were obtained for both the 33:O:O and 66:O:O schedules except that the terminal level of performance was lower for the 33:O:O schedule. An analysis of the learning curves provided additional information regarding the developmental changes in choice behavior. The trend toward maximizing was apparent for the 3- and 5-year-olds even in the first block of 10 trials (cf. Jones & Liverant, 1960) and they rapidly approached an asymptote approximating 80% choice of the reinforced stimulus. In contrast, the performance of the college students, even while reaching the same asymptote, approximated 35% choices of the reinforced stimulus for the first block of 10 trials. The responses of 7-, 9-, 11-, and 15-year-olds were best characterized by left, middle, right (LMR) or RML response patterns, presumably indicative of systematic, redundant search strategies involving the three stimuli. The youngest and college subjects’ behavior was best characterized by perseveration to the reinforced stimulus, whether or not the response had been reinforced on the preceding trial. It should be noted here that Crandall, Solomon, and Kellaway (1961) also found no differences over 80 trials between the performance of adolescents (CA = 15-17 years) and younger (CA = 6-8 years) children on an 80:20 two-choice task (simultaneous procedure, noncontingent information feedback, trial-defined schedule). In addition, Lewis, Wall, and Aronfreed (1 963) found no differences in performance between first- and sixth-grade children on a 70: 30 task (simultaneous procedure, contingent information feedback, trial-defined schedule).

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Kessen and Kessen (1961) using 70:30 and 50:50 schedules (successive procedure, noncontingent information feedback, trial-defined schedule) found no differences between groups of 3.6- and 4.4-year-old children in probability learning. Lewis (1966) also found greater trends toward maximizing for nursery school (CA = 3-5 years) than for firstand second-grade children on a two-choice 70:30 task (successive procedure, noncontingent information feedback, trial-defined schedule). Apparently, the data described by Weir (1964) are highly reliable and can be generalized across a variety of tasks, procedures, reinforcement schedules, etc. Similar results have been obtained when tasks involving random reinforcement have been used. Although only a few sets of data are available, alternation or systematic search behavior is found in normal children above the age of four (Goulet & Barclay, 1967; Jeffrey & Cohen, 1965; Rieber, 1966) and perseveration is found in subjects who are younger than four (Jeffrey & Cohen, 1965). This developmental trend from perseveration to alternation is also apparent in retarded children when MA rather than CA serves as the index for differentiating the subjects (Goulet, 1969). It is of interest to note that Schusterman (1964) and Metzger (1960) also found a trend toward alternation in the probability learning of retardates with MA’s between 5 and 6 years. Gerjuoy and Winters (1 968) have documented further evidence for this conclusion. Two additional studies (Derks & Paclisanu, 1967; Goodwin, 1969) also relate to the same general problem and provide data on probability learning across a wide age-range. Derks and Paclisanu compared nursery (mean CA = 4.3 years), kindergarten (mean = 6.6 years), first-grade (mean CA = 6.9 years), second-grade (mean = 8.0 years), fifth-grade (mean CA = 11.1 years), seventh-grade (mean CA = 12.9 years), and college (mean CA = 21.3 years) subjects over 200 trials on a two-choice 75: 25 task (simultaneous procedure, noncontingent information feedback, trial-defined schedule) and again found that selection of the more frequent event varied as a U-function of age. This was true whether performance was compared over the first 100 trials or the second 100 trials, and even though all groups were responding at a higher terminal level on Trials 101-200. The nursery school children manifested strong “positive recency” effects (increased probability of predicting an event as that event continues to occur) on Trials 1-100, with a switch to maximizing on Trials 101-200. The behavior of kindergarten children was best characterized by alternation, although positive recency effects were also manifested in the first block of 100 trials. The third-, fifth-, and seventh-grade children, for the most part, were not characterized by any apparent, general perseveration strategy. The college subjects

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showed an increasing trend toward perseveration with increasing practice. The one disparity between the results of Weir (1 964) and of Derks and Paclisanu relates to the kindergarten children. Weir found that the behavior of these subjects was similar to that of the nursery school (i.e., maximizing) children. Derks and Paclisanu found that the performance of the kindergarten children was depressed below that of the nursery school subjects and was more like that of the first-grade subjects over the number of trials used by Weir ( 1 964). In addition, Weir’s kindergarten subjects tended toward perseveration to the most frequently reinforced stimulus, but those of Derks and Paclisanu showed alternation behavior. There were a number of differences between the studies, including the number of choices [three (Weir) versus two (Derks and Paclisanu)], type of feedback [contingent (Weir) versus noncontingent (Derks and Paclisanu)], and type of schedule [response-defined (Weir) versus trial-defined (Derks and Paclisanu)]. Any of these differences could account for the disparities in results. However, it is useful to note that alternation behavior in children approximately 5 years of age has been found by Craig and Myers (1963), who used both 80:20 and 60:40 reinforcement schedules (simultaneous procedure, noncontingent information feedback, trial-defined schedule), and by Jeffrey and Cohen (1969, who manipulated random reinforcement (loo%, 50%, 33%) in a two-choice task. In fact, Craig and Myers found that the performance of kindergarten children was similar to that of fourth-grade children (but displaced below that of eighth-grade children) on Trials 1-120 but was strikingly below that of the fourth-and eighth-grade subjects on Trials 12 1-200 (a finding very similar to that of Derks and Paclisanu). A detailed consideration of the effects of task differences is contained elsewhere in the paper. However, recent data collected at West Virginia University (Goodwin, 1969) do provide some information regarding task- and age-differences across the same age-span considered by Weir (1 964) and Derks and Paclisanu. Goodwin (1 969) compared performance in probability learning as a function of the number of choices (two, three) and type of information feedback (contingent, noncontingent) across much the same age-range used by Weir (1964) and Derks and Paclisanu ( 1 967). The subjects were kindergarten (mean CA = 5.1 years), second-grade (mean CA = 7.6 years), and fifth-grade (mean CA = 10.9 years) children and college students. The reinforcement schedule (trial-defined)was 75:25 for the twochoice and 75: 12.5:12.5 for the three-choice task. Information feedback as to the reinforced stimulus on each trial was either contingent on choosing the stimulus that was keyed “correct” on that trial or was provided independently of the response made (noncontingent condition).

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Figure 2 provides summary data for responses to the most frequently reinforced stimulus in each of 6 blocks of 16 trials for the 4 age groups. These data (pooled over type of information feedback and number of choices) are remarkably similar to those of Weir ( 1 964). That is, on the first block of trials, the performance of college, fifth-grade and secondgrade subjects was similar and depressed below that of the kindergarten subjects. However, the terminal performance of the kindergarten and college subjects approached maximizing, and that of the second-grade and fifth-grade subjects was below the other two groups. Overall performance and performance in the last block of trials varied as a U-function of age, again in line with the results of Weir. As Weir suggested, markedly different processes are involved in probability learning in the different age-groups and this is reflected in the slopes of the learning curves of the four groups of subjects. In addition, similar U-functions were found whether performance was obtained with a two-choice or a three-choice task and whether information feedback was contingent or noncontingent. In an analysis of the effects of reinforcement or nonreinforcement of responses to the most frequently reinforced stimulus, Goodwin (1 969) found that the percentage of “win-stay” and the percentage of “lose-

Fig. 2. Mean percentage correct responses per block of 16 trials for kindergarten (K), second-grade (2), fifth-grade (5), and college (CON.)subjects (adapted from Goodwin, 1969).

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stay” responses vaned as a U-function of age, again in line with the results described by Weir ( 1964). In a sequential analysis of her data, Goodwin (1969) used the Index of Behavioral Stereotypy developed by Miller and Frick (1949). This measure, adapted from information theory, provides an index of the percentage stereotypy (or redundancy) of response sequences varying in length. That is, the first order of approximation (C,) provides a percentage estimate of perseveration -the degree to which the subjects choose certain stimuli with disproportionate frequencies. The second order of approximation (C,) involves successive sequences of two responses. Again, to the extent that subjects choose successive stimuli in an orderly (i.e., non-chance) fashion, C , will exceed zero. The third order of approximation (C,) provides a similar estimate except that it reflects the stereotypy of patterns three responses in length. The differences in stereotypy between successive orders of approximation (e.g., C, and C,) reflects the additional redundancy accounted for by the analysis of more complex response patterns. Figure 3 provides summary data on the Index of Behavioral Stereotypy for each of the age-groups used by Goodwin. The data reflect stereotypy measures for data pooled over 96 trials and over the other treatments. The stereotypy of the kindergarten was reflected primarily at C, (indicating strong perseverative behavior). The college subjects also had greater stereotyped behavior at C,; however, the stereotypy at C , and C , for these subjects did not differ from that of the second- and fifthgrade children. In other words, even though strong perseverative behavior was found for the college subjects, their sequential responding was still quite variable relative to the kindergarten children. This function for the college subjects most likely reflects a search for a response pattern involving 100% reinforcement (Weir, 1964) and which, nevertheless, involves disproportionate choice of the most frequently reinforced stimulus. The behavior of second- and fifth-grade subjects, in contrast, was less stereotyped than the kindergarten and college subjects even at C1.

D. VARIABLES

INFLUENCING PROBABILITY LEARNING:

TASKVARIABLES

1. Schedule of Partial Reinforcement The studies concerned with the probability learning of children have, for the most part, compared the performance of subjects under more than one schedule of partial reinforcement even though there has been little direct theoretical interest in this variable. Brunswik (1939) has suggested that the task can be used to obtain children’s “thresholds”

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Fig. 3 . Mean response stereotypy for kindergarten ( K ) , second-grade (2). jiifth-grade ( 5 ) , and college (Coll.)subjects pooled over 96 trials (adapted from Goodwin, 1969).

for discriminating a deviation from chance probability. However, the probability-learning task has not been used with children specifically for this purpose. Terminal performance has been found to vary directly with the level of reinforcement for the most frequent event (e.g., Little, Brackbill, Isaacs, & Smelkinson, 1963) and no exceptions have been found. In addition, even nursery school children can discriminate a 60:40 schedule from a 50:50 schedule. [Brunswik ( 1 939) has suggested that the “probability threshold” for rats is near .70.] However, for purposes of determining thresholds, it is perhaps of interest to note that the event schedules can be programmed independently for each stimulus. For example, schedules of 60:50, 90:80, 20:10, etc., can be used. And, if a simultaneous procedure is used and contingent information feedback is provided, subjects do not have to be made aware that any (or no) stimuli will be reinforced on any particular trial.

2. Number of Choices Two studies (Goodwin, 1969; Weir & Gruen, 1965) have dealt with the probability learning of children as a function of the number of choices in the task. Weir and Gruen (1965) compared preschool children (mean CA = 4.4 years in Exp. I, 4.7 years in Exp. 11) on 75:25 and 75:12.5: 12.5

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tasks (simultaneous procedure, contingent information feedback, trialdefined schedule) and found that terminal performance (after 96 trials) was higher tor the two-choice than for the three-choice task. This was true whether the task involved button pushing (Exp. 11) or involved guessing which of two toy milk bottles contained a prize. These findings contrast with the results of a number of other studies using young adult subjects. For example, Gardner (e.g., 1957, 1958) and Cotton and Rechtschaffen (1958) have found that terminal performance is higher in young adults as the number of alternatives is increased. Weir and Gruen suggested that the apparent disparity in results is a function of the type of information feedback (i.e., terminal performance is higher for a three-choice task with noncontingent feedback but lower with contingent feedback) rather than age differences. However, Neimark (1956), again using young adult subjects, has found that terminal performance was equal for two- and three-choice tasks whether contingent or noncontingent information feedback was provided. Goodwin (1969) compared the probability learning of subjects from kindergarten through college age and varied both the number of alternatives (two, three) and type of information feedback (contingent, noncontingent). Therefore, some additional information is available relative to the interaction of age, number of alternatives, and type of information feedback. Figure 4 shows mean responses to the reinforced stimulus pooled over 96 trials for Goodwin’s four age levels. The data are provided for treatments involving contingent and noncontingent information feedback. As Fig. 4 indicates, there is little regularity across the age groups regarding the effects of type of information feedback. Weir and Gruen’s ( 1965) results indicating higher performance for five-year-olds on a twochoice task were replicated under conditions of contingent information feedback. Performance was also better on the two-choice task for fifthgrade children under contingent reinforcement. Gardner (1 957) has suggested that performance in a three-choice task increases relative to a two-choice task with an increasing number of trials (e.g., 450 trials) for young adults. However, the effect of increasing the number of trials remains to be explored in children.

3. Apparatus and Procedural Digerences Extremely little research has been directed to the study of task and procedural differences as they affect children’s probability learning. Offenbach (1 965) has compared the performance of kindergarten (mean CA = 5.5 years) and fourth-grade (mean CA = 9.6 years) children on a two-choice task with 90: 10, 75:25, and 60:40 reinforcement schedules

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Fig. 4. Mean percentage correct responses for kindergarten ( K ) , second-grade ( 2 ) , fifth-grade (5), and college (Coll.) subjects in 2- and 3-choice tasks with contingent or noncontingent information-feedback (adapted from Coodwin, 1969).

(noncontingent information feedback, trial-defined schedule) as a function of method of presentation (simultaneous or successive). No task differences were found except for a trend toward higher terminal performance under the simultaneous procedure for the 75:25 schedule. No interactions with age were found. Weir and Gruen (1965) used preschool subjects (mean CA = 4.5 years) and tasks involving button pushing or predicting which of two (or three) milk bottles contained a prize, and found that children performing on the latter task made significantly fewer correct responses. They speculated that the milk-bottle task was much more boring and thereby resulted in more response variability in these subjects. No interactions with type of incentive or number of response alternatives were found. However, the small amount of research related to these problems makes any generalization tenuous. 4. Instructional Effects A basic assumption in probability learning experiments is that subjects

enter the task with the belief that a solution is possible and that there is a method of obtaining reinforcement on every trial. It follows that instructions to the contrary (e.g., telling subjects that there is no solution or that it is impossible to be correct on every trial) will increase

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the frequency of predicting the most frequently reinforced stimulus. Similarly, instructing subjects that 100% success is possible should increase the variability of responding and thereby reduce the number of choices of the correct stimulus. Goodnow (1955) has found that young adult subjects with a “gambling’’ (no solution) set more closely approximated maximizing than did subjects with a “problem-solving” (solution) set. However, similar studies with children (Gruen & Weir, 1964; Weir, 1962) have had little success in modifying their choice behavior. This is true even though Stevenson and Weir ( 1 963) found that children (CA = 12- 18 years) entered the task with a strong expectancy that the task had a solution. Weir (1962) used a three-choice task and a 50:O:O reinforcement schedule (simultaneous procedure, contingent information feedback, response-defined schedule), and found that terminal performance of 5- to 7- and 9- to 13-year-olds was unaffected by instructions implying that the problem did not have a solution. Gruen and Weir (1 964) noted that the effects of a gambling set may be due to the “risk” aspects of the gambling task (penalizing subjects for an incorrect choice) rather than due to a “set” not to expect 100% success. With a 66:O:O reinforcement schedule and children approximating 7.6 and 13.5 years and college subjects, they factorially manipulated instructional set (solution, no solution, or neutral instructions) and penalty/no penalty for incorrect choices. Penalty for incorrect choices increased the selection of the correct stimulus for all subjects, but instructions had an effect only for the college subjects. The “no solution” and “solution” sets increased and decreased the selection of the reinforced stimulus, respectively, for the college subjects. E. TRANSFER OF TRAINING

The use of transfer tasks typically represents an extremely sensitive method for determining the effects of past experience. When applied to probability learning, a variety of transfer designs can be constructed. For example, subjects can be trained on one reinforcement schedule and can then be switched to another schedule varying in any of a number of ways from the first. The second schedule (task) may involve the same solution (most efficient strategy) as that required (or learned) in the first task, in which case performance in the second task should be facilitated as a function of first-task practice. For example, practice on a 66:O:O schedule - involving reinforcement for responding to the left (L) stimulus and no reinforcement to the right (R) and middle (M) stimuli-requires a “strategy” of maximizing. The second task may be identical in all respects to the first except that a 33:O:O schedule is

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used. Here, subjects can transfer both the solution (maximizing) and the response to be chosen (L). This design may be called a solution identical, response identical paradigm. Two sources of positive transfer are apparent; i.e., transfer of the solution and transfer of the response from Task 1 to Task 2. Transfer paradigms may also be generated such that one or more aspects of the second task are interfered with as a function of practice on the first; e.g., a solution identical, response different paradigm can be constructed. In this case, subjects could transfer the solution (e.g., maximizing) but optimal performance on the second task would require a change of the response (e.g., L to M) to which the subjects maximized. In this paradigm, a source of positive transfer (solution transfer) and a source of negative transfer (response transfer) would be present. Alternatively, solution different, response identical and solution different, response different paradigms could be constructed. It is apparent that a large number of different transfer tasks could be devised depending upon the solution, number of stimuli, and reinforcement schedules used. Extremely little research has been conducted within the framework of a transfer design. However, the transfer task can be useful in developmental research on probability learning. As an example, Weir (1 964) has suggested that very young children (e.g., CA = 3 years) do not respond in probabilistic tasks by formulating strategies and testing hypotheses. Rather, he suggested that they respond only on the basis of a simple reinforcement notion. If this is true, their performance on solution different, response identical and solution identical, response identical transfer tasks should be similar (given that other factors are held constant). As is the case with transfer studies, the tasks would be designed such that Task 2 is identical for all subjects and Task 1 would be varied. Similarly, strong negative transfer would be expected for these subjects if a change in response was required from Task 1 to Task 2. The sources of negative transfer as a result of switching the task solution from Task 1 to Task 2 would be expected to be greatest at the age when strategies are first formulated (e.g., CA = 5- 10 years) after which the negative transfer resulting from changing solution from Task 1 to Task 2 should decrease. Stevenson and Weir (1959) did compare transfer in children (CA = 7.5- 10.3 years) in a solution-identical, response-identical paradigm as a function of the first- and second-task schedule of reinforcement (factorially manipulated) and found that performance on Task 2 varied as a function of the first-task schedule (100:0:0,66:0:0, 33:0:0, and 0 : O : O ) and second-task schedule. Performance on Task 2 under 66:O:O and 33:O:O schedules was ordered as a direct function of the schedule on Task 1, a result that could be predicted from a view that considers

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learning to be a direct function of the number of reinforced trials. However, the ordering of performance was inconsistent under 0:O:O and 1OO:O:O schedules on Task 2, an indication that the transfer of the solution was an important factor in terms of Task 2 performance. Whether the same results would be found had the reinforced stimulus been changed on Task 2 is unknown. Jones and Liverant (1960) compared nursery school (CA = 4-6 years) and elementary school (CA = 9-1 1 years) children on an 80:20 transfer task (solution identical, response different paradigm) after training on either 70:30 or 90: 10 schedules. Consistent with the present hypothesis, initial performance on the transfer task for the nursery school children was depressed considerably below that of the elementary school children. In other words, the younger children had considerable difficulty in changing their response on the transfer task. However, this was true only during the initial trials on Task 2. During the later stages of practice similar terminal performance was evident for both groups of children. Similar results were found for both schedules of reinforcement on Task 1. In another early study, Kessen and Kessen (1961) compared young children (Median CA = 3.6 and 4.5 years) under a solution-identical, response-identical paradigm. The subjects were trained on 70:30 or 50:50 reinforcement schedules on Task 1 and were either maintained on the same schedule or were switched to the alternate schedule. The younger subjects continued to respond in the transfer task as if there had been no switch of reinforcement schedule, while the older subjects modified their choice behavior to conform to the schedule of the second task. Crandall et al. (1961) compared adolescents (CA = 16-18 years) and young children (CA = 7-9 years) on two probability-learning tasks involving “patterned” schedules of partial reinforcement. Task 1 involved an 80:20 schedule where the most frequent stimulus occurred 4 times, followed by one occurrence of the least frequently occurring stimulus in each block of 5 trials. Thus, it was possible to predict the occurrence of the 2 stimuli with 100% success. Task 2 (5050 schedule) involved 5 successive presentations of each stimulus in alternate blocks of 5 trials. While both groups of subjects responded to each stimulus with equal frequency on the transfer test, the “apparent” probability matching in the older subjects was accounted for, in large part, by correctly anticipating the response pattern present in the task. In contrast, most of the younger subjects did not anticipate the pattern and responded to the two stimuli in an unpatterned fashion in each block of 10 trials. Goodnow and Pettigrew (1955, 1956) have conducted transfer studies with college students and the results are of interest here. Goodnow and Pettigrew (1955) devised an interesting variant of the typical trial-defined reinforcement schedule. In these variant schedules each stimulus

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was keyed correct according to a predefined level (e.g., 50:50) over a larger block (long run) of trials. However, within each of a number of subblocks the reinforcement contingencies were varied around the longrun schedule. For example, the reinforcement schedule over 70 trials was 50:50 but within each block of 10 trials the schedules were 80:20, 70:30, 60:40, 5 0 5 0 , 40:60, 30:70, and 20:80. It is emphasized that in the usual procedures, the schedules over subblocks of trials and over the entire series of trials are identical, or in Goodnow and Pettigrew’s (1955) terminology the reinforcement schedule is defined over the short run. As Goodnow and Pettigrew (1955) have indicated, the long-run 50:50 schedule reinforces a win-stay, lose-shift strategy, but in the shortrun 50:50 schedule subjects develop a win- ?, lose-stay strategy because they try to operate on the basis of the probable length of a run of payoffs to a particular stimulus. Conceived in another way, the long-run schedules may be seen as a series of transfer tasks involving the same solution or strategy (maximizing) with the reinforced response being identical or shifting depending on the way the schedule changes between the blocks of trials. As Goodnow and Pettigrew (1955) have found, college students do adopt a win-stay, lose-shift strategy when practicing on a long-run schedule. Furthermore, and consistent with the present hypotheses, these subjects change response very easily in a transfer task as long as the schedule changes are discriminable (Goodnow & Pettigrew, 1955, 1956) and the solutions are similar between the two tasks (Goodnow & Pettigrew, 1956). Schusterman (1963, 1964) has found that young, normal children (CA = 3-5 years) and retardates of comparable MA were not sensitive to changes in the reinforcement schedule when it was defined in a long run manner. Rather, the children responded in a consistent fashion over the block of trials independent of the reinforcement schedule within each block. Ten-year-olds, in contrast, performed in much the same manner as had Goodnow and Pettigrew’s (1955) college students. A final series of transfer studies by Bogartz ( 1966) provides additional evidence that 4- and 5-year-old children have difficulty in changing solutions between two tasks involving binary prediction. In Experiment I, 5year-olds practiced on a task involving alternation (i.e., predicting 1 ,O,l ,O,l . . . sequences) and then were shifted to a task involving recurrent ( 1 ,O,O or 1 ,O,O,O) sequences. The children quickly learned the alternation problem, but the transfer tasks were not learned. In addition, performance on the simple alternation problem was negatively affected if the subjects had previous practice on recurrent sequences (even though the children did not “learn” or master the first task prior to the initiation of practice on Task 2). In Experiment 11, Bogartz found that transfer to

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an alternation problem was similar whether the children had practiced on a Task 1 where repetitive, alternation, or random choice behavior was reinforced. The transfer tasks in Experiment I1 conformed to solution different, response identical paradigms according to the terminology adopted in this paper. Performance in probability-learning tasks may also be considered to be a function of preexperimental learning or different levels of cognitive development. Thus, performance in probabilistic tasks may be considered to reflect strategies for hypothesis testing that subjects bring to the laboratory. As such, the probabilistic tasks may be designed to capitalize on or interfere with these preexperimental strategies. Weir (1 964) has noted that children older than 5 years can generate complex hypotheses and that these are reflected in a large number of LMR and RML response patterns in a three-choice task. College subjects can test and reject hypotheses, but younger subjects are assumed to be limited in the ability to generate more complex hypotheses or in the ability to process confirming or disconfirming information in the probability-learning task. Odom and Coon ( 1966) compared the performance of 6-, 11-,and 19year-old subjects in a three-choice task where the solution involved generating LMR or RML sequences. Fewer of the youngest subjects (45%) were able to master the task in 90 trials than were the 1 1- (60%) and 19year-olds (80%). Of the subjects who had mastered the task, 11- and 19year-olds quickly rejected the LMR and RML patterns on extinction trials when they were no longer reinforced; but no extinction of the LMR and RML patterns was evident for the 6-year-olds, again suggesting that a change in solution is difficult for children in this age-range. F. THEORETICAL INTERPRETATIONS OF AGECHANGES IN PROBABILITY LEARNING

The consistency of results across variations in tasks, procedures, reinforcement schedules, etc., has already been documented. Furthermore, the notable absence of interactions with age for the experimental variables most frequently manipulated makes it more simple to concentrate on the general processes involved in probability learning and the changes in these processes that are associated with age. That is not to say that selected experimental variables (e.g., penalty, level of reinforcement) do not affect children’s performance in probability learning. However, the effects of these variables are apparently consistent across a fairly wide age-range. A number of investigators (e.g., Stevenson & Weir, 1959; Stevenson & Zigler, 1958; Weir, 1964) have noted that subjects enter the proba-

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bility-learning task with strong expectancies that the task has a solution and that prediction with 100% success is possible. In addition, subjects enter the task with hypotheses or strategies either general or specific in nature and then systematically reject these strategies when they do not provide a “solution” that meets or approximates the level of success they expect. These conclusions highlight two general problems concerned with (a) the developmental changes in the complexity of the strategies that subjects bring to the task, and (b) the developmental changes related to the systematic elimination of strategies that have been rejected. Even a cursory look at the learning curves taken from Goodwin’s (1969) study (Fig. 2) reveals the striking age-differences found. The performance of the youngest children (i.e., 5-years) was characterized by a rapid rise to an asymptote approximating maximizing, and this was reflected even in the first block of trials. In contrast, the initial performance of second- and fifth-grade children and college students was much more variable and depressed below that of the kindergarten children. The asymptotic performance for the college students, however, approached that of the kindergarten children; less performance change over trials was found in the second- and fifth-grade children. As mentioned earlier, strikingly similar results were obtained by Weir (1 964). The differences in performance on the initial trials reflect different characteristic and replicable (Derks & Paclisanu, 1967; Weir, 1964) patterns of responding (strategies) among the age-groups. The college subjects enter the task with complex strategies or hypotheses, but systematically reject them and, according to Weir (1964), finally arrive at a solution approximating that of maximizing to the most frequently reinforced stimulus. The low initial performance of the second- and fifthgrade children does reflect the capacity to generate complex hypotheses (any of which will depress performance); however, the small performance change across trials reflects either an inability to generate alternative hypotheses when they fail, or an inability to reject an hypothesis or strategy when it does not lead to the expected level of success (Weir, 1964). Weir ( 1 967) has suggested that the inability of children between 7 and 10 years of age to reject simple strategies is due to inadequate memory of past events and outcomes. To test this hypothesis, he provided 9year-old subjects with a memory aid (which provided them with an accurate record of past responses and outcomes) in a 66:O:O task (simultaneous procedure, contingent information feedback, responsedefined schedule). Consistent with his hypotheses, better performance was found with the memory aid than when it was not provided. The per-

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formance of college students (who can process information about and recall past events and outcomes) was similar whether or not the memory aid was provided. The presence of the memory aid retarded the performance of 6-year-old children (who were not expected to profit by its presence). While the above results appeared extremely promising, Weir was later unable to replicate the finding for the 9-year-olds (Weir, 1968). Weir (1964) has also suggested that the capacity to process information and to reject hypotheses should vary with the number of alternatives in the probability-learning task. That is, Weir suggested that the age for maximum variability in responding should be found at younger ages (i.e., 6-9 years) for two-choice tasks than for three-choice tasks, in which he estimated the apex to occur between 9 and 11 years of age. In other words, the increased complexity of the three-choice task was assumed to require an increased capacity to store and process information. Thus, at an age when young children would be able to reject alternation as a strategy in two-choice tasks, they may not be able to reject R M L or LMR strategies in a three-choice task. The data provided by Goodwin (Fig. 4) give some evidence for this contention especially under conditions of contingent information feedback, typically used by Weir ( 1 964). The present analysis of the probability-learning task in terms of transfer mechanisms (discussed in Section 11, E) can be extended to account for the developmental changes in performance. It can be assumed (e.g., Weir, 1964) that very young children (e.g., 3-4 years) do not formulate and test strategies in probability learning, but that their performance is a direct function of responding to the reinforced stimulus. With increasing age, the data suggest that complex patterns of responding are generated, denoting a shift in process away from responding on the basis of a simple reinforcement notion and toward one which can be labeled problem-solving. The adoption of a problem-solving set necessarily leads to an increase in the variability of responding in probability learning and, directly correlated, a decrease in responding to the maximally reinforced stimulus. The very fact of variable responding implies that different patterns of responses (varying as to type and length of response sequence) will be reinforced (on a partial reinforcement schedule) across trials. The youngest children capable of generating complex strategies should thus have difficulty in filtering out response patterns that are differentially reinforced; however, older children should have less difficulty in doing so. The above interpretation is similar to that provided for transfer tasks except that in the case of probability learning on a single task, the solution is subject-generated and the source of negative transfer is attributable to intratask solution interference. In a transfer paradigm, the solu-

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tion is experimenter-defined and the source of solution transfer is an inter-task variable. For the most part, however, these hypotheses can best be tested in a transfer design. As stated previously, performance on a second task can provide much information related to the manner in which subjects were responding on the first task. G. INCENTIVE

The primary concern here is to determine whether magnitude of reward or type of incentive interacts with age in probability learning. It is important to note that the provision of incentives (reward) plays a dual role in probability learning tasks, that of providing information feedback for correct prediction and that of rewarding these choices. N o studies have systematically manipulated contingent/noncontingent information feedback and incentive level to determine the separate effects of each variable. For the most part, studies varying incentive level provide reward (typically candy or a small toy) or information feedback (instead of the reward) if correct predictions are made. The effects of reward for correct predictions have also been studied in conjunction with penalty for incorrect choices (Das RC Panda, 1963; Gruen & Weir, 1964; Offenbach, 1964). In these studies correct predictions result in obtaining reward and incorrect predictions result in giving up a reward object. Again, it is possible to manipulate factorially the reward and penalty variables. One additional consideration in the investigation of the effects of penalty should be mentioned. In probability learning tasks involving penalty treatments, subjects are punished for making both incorrect and correct responses. For example, consider a 66:O task. The subjects will be penalized for one third of the responses to the reinforced stimulus and will be rewarded for the remaining twothirds of their responses to this stimulus. Thus it is apparent that maximizing will be adopted as a strategy only if the cumulative effects of reward are greater than those of penalty. The problem becomes more complex if the reinforcement schedules used provide for reward and punishment of alternative responses (e.g., a 75:25 schedule). 1. Tangible Reward The effects of varying incentive level have been consistent for all age levels except for 3- to 5-year-olds. Brackbill, Kappy, and Starr (1962), using second-grade children (mean CA = 8.0 years) and a two-choice task (75:25 reinforcement schedule, successive procedure, noncontingent information feedback, and a trial-defined schedule), found that one, three, or five marbles (which could be turned in for a toy) as reinforcers

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for correct predictions led to higher terminal performance than providing information feedback alone. However, there were no differences between the one-, three-, and five-unit groups. Bisett and Rieber (1966) scaled incentives for children (CA = 6-7 and 10-1 1 years) and then varied the reward (most vs. least preferred in a two-choice probability-learning task (3 3 :O schedule, simultaneous procedure, contingent information feedback, response-defined schedule) and again found that performance with high incentive reinforcers was better than that with low incentive reinforcers. However, the performance differences between the high- and low-incentive treatments could have been due to the facilitative effects of high incentive or to interfering effects of low incentives (or both) relative to providing information feedback alone. Similarly, Stevenson and Hoving (1964), using children (mean CA = 9.4 and 13.7 years), found that reinforcement with incentives of high value (nickels) led to higher asymptotic levels of response than did incentives of low value (metal washers). This was true for both 66:O:O and 3 3 :O:O schedules (simultaneous procedure, contingent information feedback, response-defined schedule). However, opposite results occurred for preschool children (mean CA = 4.6 years). With college students, no differences in performance were found as a function of incentive-level. Stevenson and Weir (1959) have also found higher terminal levels of performance for 5-year-olds when low (marbles) relative to high (trinkets) incentives were used. Siegel and Andrews (1962), also using young subjects (CA = 3.8-5.0 years) and a 75:25 task (simultaneous procedure, noncontingent information feedback, trial-defined schedule), found that reinforcement with small toys (high incentive) facilitated performance relative to the provision of information feedback alone. Weir and Gruen (1965) attempted to reconcile the disparate findings of Siegel and Andrews ( 1 962) with those of Stevenson and Weir ( 1 959) and Stevenson and Hoving (1964) with 4- and 5-year-olds. They varied the task and number of response alternatives (two vs. three). With twochoice tasks the reinforcement schedule was 75:25, and with threechoice tasks the schedule was 75: 12.5:12.5. With a two-choice task which replicated the procedure of Siegel and Andrews (except that contingent information feedback was used), high incentive (small toys) led to higher terminal performance. With a three-choice task no differences in performance between the incentive treatments were found. Furthermore, when the incentive-level was switched after 96 trials (highjlow or low+high) these groups showed a marked increase in the number or choices to the most frequently reinforced stimulus. No such change was apparent for subjects who were maintained on the same (highjhigh, low+low) incentive level for 192 trials. The increase in terminal per-

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formance for the incentive-switch groups was apparent for both two- and three-choice tasks. When a task similar to that of Stevenson and Weir (1 959) and Stevenson and Hoving (1 964) was used, lower terminal performance was found for the high incentive treatment. This was the case for both two- and three-choice tasks.

2. Penalty Das and Panda (1963), Offenbach (1964), and Gruen and Weir (1964) have compared children’s probability learning under what may be called reward-penalty conditions (where subjects are rewarded for correct predictions and forfeit rewards for incorrect predictions). Again, the data across studies are inconsistent. Das and Panda (1963), used a 75:25 reinforcement schedule (successive procedure, noncontingent information feedback, trial-defined schedule) and 5- to 7- and 13- to 14-year-old children, and found that a reward-penalty treatment led to inferior performance relative to a treatment involving information feedback alone. Offenbach (1964) also used a 75:25 schedule (successive procedure, noncontingent information feedback, trial-defined schedule), with kindergarten (CA = 4.4-6.4 years) and fourth-grade (CA = 9.3-1 1.8 years) subjects, but found higher terminal performance under reward-penalty conditions relative to information feedback alone. The reasons for the disparate results of Offenbach ( 1964) and Das and Panda (1963) are not apparent. Gruen and Weir (1 964) did find that a rewardpenalty treatment resulted in superior performance for 7- and 13-yearolds and for college subjects relative to reward (marbles) alone. 3 . Social Reinforcement For the most part, studies of probability learning have provided information feedback alone for correct responses. In some cases, a reinforcer (e.g., marbles) was provided for correct responses and these could be traded in for “prizes” at the termination of the task. Another group of studies of probability learning have investigated the effects of social reinforcers (e.g., approval, disapproval) alone or in conjunction with the effects of other sociopsychological variables. Lewis et al. ( 1 963) found that positive social reinforcers provided by the experimenter (statements of “Good,” “Fine,” for correct responses) were much more effective than information feedback alone for firstgrade children performing on a 70:30 probability-learning task (simultaneous procedure, contingent information feedback, trial-defined schedule). No differences in performance were apparent in the effects of social and nonsocial reinforcement when sixth-grade children served as subjects. However, this effect is apparently restricted to conditions in which the experimenter maintains an aloof relationship with the child

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(Dorwart,Ezerman, Lewis, & Rosenhan, 1965), or when the child has been socially deprived (left alone) for a short period of time (Lewis, 1965; Lewis & Richman, 1964) or has a somewhat negative social encounter with the experimenter (Lewis & Richman, 1964). Furthermore, Stevenson and Weir (1963) found that children’s performance in a probability-learning task was unaffected by the presence or absence of the experimenter or a peer in the experimental situation. In addition, McCullers and Stevenson (1960) found that verbal reinforcement was an effective reinforcer for 3- and 4-year-old children but not for 8- and 9year-old children. Rosenhan ( 1 966) has also found that social approval was more effective than social disapproval for lower-class white and black children in a task similar to that of Lewis et al. ( 1 963). Social approval and disapproval were equally effective for middle-class white children. Unfortunately, there is a paucity of data relating to the interaction of age with type of social reinforcement. Lewis et al. (1963) did find that the facilitative effects of a positive social reinforcer were not apparent for sixth-grade children. And, the data taken together suggest that with the possible exception of first-grade and younger children, similar strategies are used in probability-learning tasks independently of the type of reinforcer provided. In addition, disapproval apparently has similar effects to penalty (penalizing subjects for incorrect choices) for first-grade children. Whether the same is true for older subjects is an empirical question needing investigation. However, as noted above, penalty conditions result in superior performance for subjects across a wide age range, but the data of Lewis et al. (1963) suggest that social reinforcers may become less effective with increased age. H. COMMUNALITY OF RESPONSEPATTERNS ACROSS TASKS AND SUBJECTS

The generality of results among the studies concerned with probability learning has already been discussed. Indeed, almost without exception the choice behavior of very young children (e.g., CA = 3-4 years) in probability-learningtasks has been characterized by perseveration independently of the reinforcement schedule, method, procedure, etc. In contrast, strong preferences for alternation (on two-choice tasks) or systematic search strategies (LMR or RML patterns on three-choice tasks), and again independent of the response-reinforcement contingencies, are found for children ranging in age from 6 to at least 1 1 or 12. Some disparate results are found for 5-year-olds. For example, Weir (1964) and Goodwin (1 969) found pronounced trends toward perseveration for these subjects, but Derks and Paclisanu ( 1 967) found that alternation best described their behavior. Presumably, differences in the sample characteristics between the groups of studies are responsible for the dis-

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parate results. Differences in task characteristics are apparently not responsible for the disparate findings.

111. Other Tasks A. HIDE-AND-SEEK BEHAVIOR

Stevenson and Odom (1964) devised an interesting variant of the probability-learning task -one in which the experimenter and subject alternated hiding and searching for small prizes. The experimenter hid prizes among three boxes according to a 75:25:0 schedule (simultaneous procedure, contingent information feedback, trial-defined schedule) and this aspect of the task was identical to the typical probability-learning situation. However, the subjects (CA = 3-5, 7-8, 10-12 years) alternated with the experimenter in hiding prizes; the experimenter, when the child hid the prize, searched randomly or according to a prearranged 75:25:0 schedule. Of primary interest is the subjects’ hiding behavior. When the experimenter was searching according to the 75:25:0 schedule, the subjects could minimize their losses by hiding the trinkets in the 0% box, but there was no best strategy when the experimenter was searching in a random manner. Although all subjects hid the trinket in the 0% box most frequently when the experimenter was searching according to a 75:25:0 schedule, the youngest children did not improve over the three blocks of 20 trials for hiding. Interestingly, the 7- and 8year-olds’ performance improved most over the three blocks of trials. When the experimenter was searching according to a random schedule, the 7- to 8- and 10- to 12-year-olds distributed their choices equally among the three alternatives. The youngest children showed a strong position preference for hiding the trinket in the middle box. The hide-and-seek task is an interesting one and has promise for the investigation of problem-solving strategies in children. A first line of inquiry, investigated by Stevenson and Odom (1964) and by Odom (1966) is directed to the determination of how children’s searching behavior is affected by the experimenter’s systematic (or unsystematic) pattern of searching. The evidence here suggests strong effects in the direction of superior performance if the experimenter is of the opposite sex (Odom, 1966). A second question is whether the processes involved in children’s hiding and searching are the same. Stevenson and Odom found no statistically significant correlations between children’s tendencies to maximize reinforcement in searching and to minimize loss in hiding. However, the correlation was low negative (r = -.34)for children with CA’s of 3 to 5 and low positive for children with CA’s of 7 to 8 ( r = .33) and 10 to 12 (r

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= .26), leading Stevenson and Odom to suggest the possibility of the

operation of a different process in the youngest group as compared to the two oldest groups. It should be mentioned that the data related to hiding and searching which were collected by Stevenson and Odom (1964) are not independent since the children alternated these activities. Hiding behavior can be investigated independently of searching. With data such as these, the similarity of the strategies in searching and hiding can be compared under treatments in which maximizing, alternation, etc., are the most efficient strategies. Furthermore, both searching (probability learning) and hiding can be compared under penalty conditions. As is apparent, failure to hide appropriately results in losing a trinket for the child-a condition which is similar to that in probability learning when the child fails to search appropriately and is penalized for his incorrect choice. In fact, the functional dissimilarity in the effects of searching and hiding in terms of reward and penalty may be the reason why no strong correlation was found between the efficiency of hiding and that of searching. However, Gratch (1964) has found similar age trends in searching and hiding behavior. Children (CA = 2-8 years) guessed (10 trials) in which hand the experimenter had hidden a marble and then hid the marble from the experimenter for a series of trials. With increasing age, the children shifted from stereotyped to less stereotyped guessing patterns and hid the marble in a less regular and thus more deceptive and competitive manner. Gratch interpreted his results as indicating that with increasing age, children have a greater ability to vary their behavior in an uncertain situation.

B. GUESSING BEHAVIOR A number of studies (Goulet, 1969; Goulet & Barclay, 1967; Jeffrey & Cohen, 1965; Rieber, 1966) have examined developmental changes in choice behavior using random reinforcement rather than reinforcement based on an experimenter-defined correct response (as in probabilitylearning tasks). When random reinforcement schedules are used, subjects are reinforced on prearranged trials, independently of which choice is made. The levels of random reinforcement selected may vary from continuous through any degree of partial reinforcement. As an example, Jeffrey and Cohen (1965) compared the alternation and perseveration behavior of children (mean CA = 3.3 and 4.6 years) in a two-choice task in which subjects were reinforced according to 100, 50, or 33 % schedules. Pronounced differences in alternation and perseveration behavior were found among the age-groups. The 3-year-olds perseverated on one response, and the 4%-year-olds alternated. These dif-

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ferences were especially apparent under the 100% schedule of random reinforcement and to a lesser degree under the 50% schedule. However, under the 33% schedule no differences were apparent between the 3and 41/-year-olds. These data suggest an interaction between level of random reinforcement and age. Additional children (mean CA = 4.1 years) were run under the 100% schedule and were found to divide themselves into two groups - those who perseverated and those who alternated - suggesting some transition in the characteristic pattern of responding in multiple-choice tasks. Rieber ( 1966) compared children (CA = 7-9 years) under random reinforcement conditions and found a strong tendency for alternation in these subjects. However, Schusterman ( 1963) used 100% random reinforcement and a two-choice task, and found that 10-year-olds showed no preference for either alternation or perseveration, while 3-year-olds again showed perseveration and 5-year-olds alternation. McCullers and Stevenson ( 1960), using a reinforcement schedule similar to random reinforcement (66:66:66 or 33:33:33 schedules; i.e., with no stimulus maximally reinforced), also found greater response perseveration for 3and 4-year-olds than for 8- and 9-year-olds. Two additional studies (Goulet, 1969; Goulet & Barclay, 1967) were also concerned with choice behavior of children under random reinforcement. Goulet and Barclay ( 1967) compared the characteristic patterns of responses over 200 trials for noninstitutionalized retardates (MA = 6-8 years, IQ = 50-70) and MA-matched normal children. A four-choice task with either 10 or 25% random reinforcement was used. Figure 5 presents summary data for the groups of subjects. The data are expressed in terms of the Index of Behavioral Stereotypy (discussed earlier). As can be seen from Fig. 5, no trend toward position perseveration was found for either the normal or the retarded children; i.e., the response stereotypy at C, approximates 0% for all treatments, implying that both groups of subjects selected the response alternatives with equal frequency over the 200 trials. Furthermore, in accord with the results of Weir (1 964) and Derks and Paclisanu (1967), who used probability-learning tasks, and Rieber ( 1966) and Jeffrey and Cohen (1963, who varied random reinforcement, the predominant response pattern when considering sequences of two responses was the selection of adjacent alternatives on successive trials. In other words, responses of (1,2), (2,3), (3,4), (4,3), etc., predominated when a frequency count of different patterns of consecutive responses was considered. When the stereotypy of sequences of three consecutive responses was considered, pronounced differences in the behavior of retardates and normals were evident. For the retardates, the third response in a sequence of three was more likely to be a response different from the pre-

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30

10 % reinforcemeni

e f

f

D

IX

20

5t

0L

t

1 Order of approximation

Fig. 5 . Mean response stereotypy for normal ( N ) and retarded ( R ) children at two levels of random reinforcement. [Adapted from Goulet and Barclay (1967) with the permission of the Society for Research in Child Development.]

ceding two. The normal subjects did not select adjacent alternatives, but the third response in a sequence of three was as likely to be any of the three remaining alternatives. Thus, the functional pool of alternative responses for normal children was three for the third response in a sequence of three, while that for the retardates was essentially reduced to two. A further finding by Goulet and Barclay (1967) was that response stereotypy was greater under the 25 % level of random reinforcement than under the 10%level for both groups, although the differences were small. Goulet (1969) also investigated the effects of random reinforcement (lo%, 33%) on the choice behavior of institutionalized retardates in a four-choice task. The MA levels were chosen to include one group (i.e., MA = 4 years) in which strong response perseveration was expected and a second group in which choice behavior was not expected to be characterized primarily by perseveration (MA = 6 years). Jeffrey and Cohen (1965), Weir (1964), and others (e.g., Derks & Paclisanu, 1967) have found that the choice behavior of normal children approximately 4 years of age is characterized by perseveration, and the behavior of older children is characterized by more complex patterns (e.g., alternation). Whether the same trend toward response perseveration can be found for retardates with MA’s approximating 4 years is of much interest. In addition, Goulet (1969) used a level of partial reinforcement much lower than those used by others. Figure 6 provides a comparison of the degree of behavioral stereotypy of response patterns as a function of MA and level of random reinforce-

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ment over the entire block of 210 trials. As can be seen, the degree of stereotypy was greater for low-MA than for high-MA retardates. In addition, the interaction of MA with length of the response pattern, although not pronounced, was statistically significant. In general, the predominant response pattern for low-MA retardates was perseveration to a particular stimulus; i.e., 1,2,3, or 4. However, no position preference was present across subjects. In other words, the greatest degree of stereotypy for these S s was at C1, with small increments in stereotypy present for the C , and C 3patterns (Fig. 6). For the high-MA retardates, the redundancy (stereotypy) in performance was much less pronounced but increased regularly from C, to C3. The interaction of MA with level of random reinforcement is also apparent in Fig. 6. The degree of stereotypy was much more pronounced under the 33 % level of random reinforcement for the low-MA subjects. Again, the effect of the level of random reinforcement was manifest primarily at C,. For the high-MA retardates, no differences in stereotypy were apparent as a function of level of random reinforcement.

70

t

I

I

CI

CE

I c3

Order of approximation

Fig. 6 . Mean response stereotypy for retarded children under two levels of random reinforcement (adaptedfrom Goulet, 1969).

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Identical results were found when the data were analyzed in blocks of 50 trials (omitting the last 10 trials). In addition, the degree of stereotypy for C, and C, patterns increased over blocks of trials for both low- and high-MA retardates. Furthermore, there was a trend toward increasing perseveration over blocks of trials for the low-MA subjects. This trend was much less pronounced for the high-MA subjects. As can be seen in Fig. 6, the low-MA retardates’ choice behavior was characterized by perseveration (greater stereotypy at C,) under both levels or random reinforcement. These data support those obtained by Jeffrey and Cohen (1969, who used random reinforcement, and those of others (e.g., Derks & Paclisanu, 1967; Weir, 1964), who used probability-learning tasks and normal children as subjects. However, the interaction of level of random reinforcement with MA-level found by Gouiet (1969) and that with CA and level of random reinforcement found by Jeffrey and Cohen (1965) suggest that the tasks involving random reinforcement may be somewhat more sensitive to developmental changes in choice behavior than those involving probability learning. In addition, the use of tasks involving random reinforcement has merit because subjects are reinforced for response patterns or strategies that they bring with them to the task. Thus, the characteristic response patterns (strategies) of all subjects, independent of age, are reinforced and presumably maintained. This is especially true for the 100% level of random reinforcement, where nonreinforcement cannot occur, as noted by Gerjuoy and Winters (1 968). However, partial random reinforcement schedules should also maintain these characteristic response patterns. C. ALTERNATION BEHAVIOR

The evidence relating to the spontaneous occurrence of alternation behavior of young children in probability learning has been amply documented. Earlier, Tolman (1925) and Wingfield and Dennis (1934) demonstrated the presence of spontaneous alternation behavior in rats performing in tasks involving two-choice mazes. Wingfield ( 1 938) also found strong alternation behavior in children with similar mazes modified for these subjects. However, alternation behavior was not as pronounced for adults in such tasks (Wingfield, 1943). The studies by Wingfield were concerned with preferences between two alternate pathways subjects could traverse to a goal. It is interesting to note that alternation behavior is found in tasks other than those involving probability learning and, furthermore, that similar developmental trends are found with these tasks. Baumeister (1966) has also documented this for normal (mean CA = 7.9 years) and retarded children on a three-choice discrimination task.

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The attempt to account for the presence and persistence of alternation behavior has prompted several theorists to specify the conditions under which alternation behavior will occur. For example, Skinner (1942) has suggested that through conditioning in childhood, a tendency is set up which opposes repetition in guessing behavior. Thus, with two-choice tasks alternation is generated because each successive response is under the control of the immediately preceding response. Similarly, Hull’s (1943) concept of reactive inhibition (Ir) was used to explain the decreased tendency to repeat a response. More recently, Glanzer (1953) has postulated a “stimulus satiation” theory, in which, with repeated exposure to the same stimuli, the subject’s tendency to respond to the stimuli is reduced. Thus, the result of stimulus satiation is “spontaneous” alternation behavior. In other theoretical accounts, Dember and Earl (1 957) have suggested that spontaneous alternation behavior is a function of a motive to optimize stimulus change, and Walker’s (1958) “action decrement” theory has considered alternation to be a function of a lowered capacity for rearousal of the same response after it has occurred. The primary purpose here is not to review these theories since thorough reviews are available in the articles cited above or in the general review by Dember (1961). Nor does the present description of the theories adequately differentiate between them in terms of their postulates or central assumptions. The above theories were not developed to account for the behavior of children, much less to account for developmental changes in alternation behavior. However, recent research with children has been stimulated by these theories and, of course, by the recurrent finding of “spontaneous” alternation behavior. Ellis and Arnoult ( 1965) have found that 4- and 5-year-old children do show decreased alternation on a simple motor task if external stimulus cues are changed from trial-to-trial, and suggested that the alternation behavior reflected a search for novelty or stimulus change. The introduction of new stimulus cues between successive trials apparently provided this novelty, whereas the novelty was response-produced (alternation) when the task stimuli were identical between trials. Croll (1966) and Ellis and Arnoult both found that spontaneous alternation decreased over practice trials and this has been observed by Jeffrey and Cohen (1965) and Bogartz and Pederson (1966) with other tasks. These findings are consistent with Glanzer’s (1953) theory. Rabinowitz and Cantor (1967), using a six-choice task with subjects instructed only to push the button to see “what lights come on,” found that 6-year-olds showed more circular behavior (pressing adjacent buttons in a systematic fashion) than did 7- or 8-year-olds and, further, that

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stimulus alternation (alternating responses which activated different stimuli) decreased over blocks of trials. Glanzer's (1953) theory apparently has some import for the study of alternation behavior. However, neither it nor any other theory relating to spontaneous alternation has been extended to account for developmental changes in choice behavior. D. STUDIES OF

THE

DEVELOPMENT OF THE PROBABILITY CONCEPT

A series of studies which received their original impetus from the results of Yost et al. (1962) was concerned with the objective assessment of the development of the probability concept in children. Yost, Siegel, and Andrews noted that Piaget (1950) had stated that children (ages 5-7) do not make predictions in probabilistic situations on the basis of quantitative proportions of elements and that they do not understand the idea of randomness nor possess a system of numerical and combinatorial operations. They questioned this assumption and devised a task in which young children (CA = 4.8-5.7 years) made decisions on the basis of objectively defined probabilities. The children saw two containers each of which contained plastic chips of two different colors in a specified proportion of one color to another. The two containers, however, contained different proportions of the two types of chips; e.g., the ratio of blue to white chips was '/3 or V5. The children were told that they were to try to draw a chip of a specified color (e.g., blue) and that they would win a prize if they drew this chip. Furthermore, they could choose the container from which to draw the chip and were fully informed of the different numbers of colored chips in the two containers. The results indicated that the children did choose the container which would maximize the opportunity to draw the payoff chip, thus suggesting that these children do have some understanding of the concept of probability. In a similar study, Goldberg (1966) found that preschool children (CA = 3.8-5.1 years) had greater difficulty in predicting which chip would be drawn as the proportion of chips of the two colors approached 5 0 . Ross (1966) obtained similar results for elementary school children in the second through eighth grades. Apparently, children in this age-range do not utilize a maximizing strategy in tasks of this nature. In other results, Ross (1 966) found that the performance of deaf children lagged behind that of hearing children in this task. This was true for 1 1-year-olds but not for older children. Finally, Ross found that children through the age of 9 did not consider the implications of choosing from the container without replacement when successive choices were made. These children demonstrated a strong tendency to alternate in predicting which of two colored balls would be drawn even though the proportion of the balls of each color changed with each successive choice. All children at

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age 6 and above solved the problem (i.e., chose the maximal payoff alternative) when verbalization of the probability concept was not required, but it was not until the age of 9 that all could both choose the correct alternative and verbalize the correct solution. Davies (1965) also used a task similar to that of Yost et al. (1962) and found that the selection of an alternative which maximized the probability of payoff varied directly with age from 3 to 9 years. An increasing percentage of children from 3 to 6 years of age selected the maximal payoff choice when the criterion for success did not involve verbalization of the probability concept. When such verbalization was required, a similar developmental trend was found except that criterion performance lagged behind that when no verbalization was required.

IV. Overview The series of studies reviewed all lead to the discussion of the same general problem -that of developmental changes in information-processing capacity. In probability-learning tasks, the issue takes the form of subjects systematically editing both strategies for “solution” of the task and the meaning of reinforcement or nonreinforcement of single responses or response patterns based on these strategies. A second theoretical issue, however, must not be overlooked- the change with age in the complexity of strategies that can be generated. In probability-learning tasks, this problem takes the form of identifying the number and type of strategies that are characteristic of subjects of different ages. With regard to this problem the evidence is most clear. These characteristic patterns change from perseveration (CA = 4 years) to alternation for children between 5 and 6 to 9 years, and to more complex search behavior through college age. Young children between 5 and 9 show strong tendencies to alternate in a wide variety of tasks (see Derks & Paclisanu, 1967; Ellis & Arnoult, 1965, Jeffery & Cohen, 1965; Ross, 1966). In transfer tasks, these same subjects have difficulty in modifying their behavior to conform to the new schedule (e.g., Crandall et al., 1961; Jones & Liverant, 1960; Kessen & Kessen, 1961) whether the transfer task involves a change in the response or responses to be made (Jones & Liverant, 1960) or in the solution to the task (Crandall et al., 1961). Apparently, the inability to conform to a new schedule is due to difficulty in rejecting a well-learned strategy (Odom & Coon, 1966). It is important to note that this difficulty is not as apparent by the age of 1 1 (Odom & Coon, 1966). The failure to find maximizing behavior in probability learning for chil-

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dren between the ages of 6 and 15 years is probably not so much due to the inability to generate complex hypotheses or strategies for solution. Weir (1964, 1967) has suggested that it is likely due to inadequate memory for past events and their outcomes. Again, the likely factor responsible here is not so much the possibility of an inadequate short-term memory store as it is the possibility of interference among competing, partially reinforced response patterns generated during the subjects’ search behavior. There is direct evidence that children at least between the ages of 6 and 9 have difficulty in processing and deducing the meaning of information based on sequential events (Ross, 1966). Although extensive research has been conducted using probabilitylearning tasks, much of the work has been exploratory, parametric, or descriptive in nature. It would now be fruitful to change direction somewhat and to generate a series of studies oriented specifically to investigating the process or processes that covary with the developmental changes in choice behavior. For example, it is possible to modify the probability-learning task such that it capitalizes on (or is inconsistent with) the characteristic behavior shown by children on these tasks. For example, the identification of characteristic patterns of responding for young children provides interesting implications which relate to the rate of learning in discrimination problems. That is, 3- and 4-year-old children should learn a two-choice position discrimination task faster than older children (e.g., CA = 6 years) because perseveration is a characteristic pre-experimental habit which younger subjects bring with them to the task. In contrast, 6-year-olds should learn a simple alternation problem much more quickly. Some support for the former prediction has been provided by Schusterman ( 1964). Along similar lines, Bogartz (1 966) and Bogartz and Pederson (1 966) have investigated some of the parameters of alternation behavior with tasks that capitalize on this response pattern or require alternation behavior as a solution to the problem. Odom and Coon (1 966) have initiated similar work. Weir (1967, 1968) has concerned himself with the identification of the mechanisms responsible for the inadequate information processing in young children. Further research along these lines should prove immensely profitable.

REFERENCES Atkinson, R. C., Bower, G . H., & Crothers, E. J. A n introduction to mathematical learning theory. New York: Wiley, 1965.

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Baumeister, A. A. Analysis of errors in the discrimination learning of normal and retarded children. Psychonomic Science, 1966, 6, 5 15-5 16. Bisett, B., & Rieber, M. The effects of age and incentive value on discrimination learning. Journal of Experimental Child Psychology, 1966,3, 199-206. Bogartz. R. S. Variables influencing alternation prediction by preschool children: 1. Previous recurrent, dependent, and repetitive sequences. Journal of Experimental Child Psychology, 1966.3, 40-56. Bogartz, R. S., & Pederson, D. R. Variables influencing alternation prediction by preschool children: 11. Redundant cue value and intertrial interval duration. Journal of Experimental Child Psychology, 1966,4,21 1-2 16. Brackbill, Y.,Kappy, M. S.. & Starr, R. H. Magnitude of reward and probability learning. Journal of Experimental Psychology, 1962, 63, 32-35. Brunswik, E. Probability as a determiner of rat behavior. Journal of Experimental Psychology, 1939, 25, 175-197. Brunswik, E. Organismic achievement and environmental probability. Psychological R e view, 1943,50, 255-272. Cotton, J . W., & Rechtschaffen, A. Two- and three-choice verbal conditioning phenomena. Journal of Experimental Psychology, 1958, 56, 96. Craig, G. J . , & Myers, J. L. A developmental study of sequential two-choice decision making. Child Development, 1963, 34, 483-493. Crandall, V. J., Solomon, D., & Kellaway, R. A comparison of the patterned and non-patterned probability learning of adolescent and early grade shool-age children. Journal of Genetic Psychology, 1961,99, 29-39. Croll, W. L. Children’s response alternation as a function of stimulus duration, intertrial interval, and trials. Psychonomic Science, 1966, 6, 247-248. Das, J. P., & Panda, K. C. Two-choice learning in children and adolescents under reward and nonreward conditions. Journal of Genetic Psychology, 1963, 68, 203-21 I . Davies, C. M. Development of the probability concept in children. Child Development, 1965.36.779-788. Demaer, W. N. Alternation behavior. In D. W. Fiske & S. R. Maddi (Eds.). Functions of varied experience. Homewood, Ill.: Dorsey Press, 1961. Pp. 227-252. Dember, W. N., & Earl, R. W. Analysis of exploratory, manipulatory, and curiosity behavior. Psychological Bulletin, 1957.64,91-96. Derks, P. L., & Paclisanu, M. Simple strategies in binary prediction by children and adults. Journal of Experimental Psychology, 1967, 73, 278-285. Donvart, W., Ezerman, R., Lewis, M., & Rosenhan, D. The effect of brief social deprivation on social and nonsocial reinforcement. Journal of Personality and Social Psychology, 1965.2, 1 1 1 - 1 15. Ellis. N. C., & Amoult, M. D. Novelty as a determinant of spontaneous alternation in children. Psychonomic Science, 1965,2, 163-164. Estes. W. K. Probability learning. In A. W. Melton (Ed.), Categories of human learning. New York: Academic Press, 1964. Pp. 98- 129. Gardner, R. A. Probability learning with two and three choices. American Journal of Psychology, 1957, 70. 174-185. Gardner, R. A. Multiple-choice decision behavior. American Journal of Psychology, 1958, 71,710-717. Gerjuoy, 1. R., & Winters, J. J., Jr. Development of lateral and choice-sequence preferences. international Review of Research in Mental Retardation, 1968, 3, 3 1-63, Glanzer, M. Stimulus satiation: An explanation of spontaneous alternation and related phenomena. Psychological Review, 1953.60.257-268.

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Goldberg, S. Probability judgments by preschool children: Task conditions and performance. Child Development, 1966,37, 157-167. Goodnow, J . J. Determinants of choice-distribution in two-choice situations. American Journal of Psychology, 1955.68, 106- 1 16. Goodnow, J . J., & Pettigrew, T. F. Effect of prior patterns of experience upon strategies and learning sets. Journal of Experimental Psychology, 1955,49, 38 1-389. Goodnow, J . J., & Pettigrew, T. F. Some sources of difficulty in solving simple problems. Journal of Experimental Psychology, 1956,51, 385-392. Goodwin. K. Changes in probability learning as a function of age, number of choices, and information procedure. Unpublished master’s thesis, West Virginia University, 1969. Goulet, L. R. Choice-behavior of retardates in a multiple-choice task under varying conditions of random reinforcement. Unpublished manuscript, West Virginia University, 1969. Goulet, L. R., & Barclay, A. Guessing behavior of normal and retarded children under two random reinforcement conditions. Child Development, 1967,38,545-553. Gratch, G. Response alternation in children: A developmental study of orientations to uncertainty. Vita Humana, 1964,7,49-60. Gruen, G . E., & Weir, M. W. Effect of instructions, penalty, and age on probability learning. Child Development, 1964, 35, 265-273. Hull, C. L. Principles of behavior. New York: Appleton-Century-Crofts, 1943. Humphreys, L. G . Acquisition and extinction of verbal expectations in a situation analogous to conditioning. Journal of Experimental Psychology, 1939,25294-301. Jeffrey, W. E., & Cohen, L. B. Response tendencies of children in a two-choice situation. Journal of Experimental Child Psychology, 1965,2, 248-254. Jones, M. H., & Liverant, S. Effects of age differences on choice behavior. Child Development, 1960,31,673-680. Kessen, W., & Kessen, M. L. Behavior of young children in a two-choice guessing problem. Child Development, 1961.32, 779-788. Lewis, M. Social isolation: A parametric study of its effect on social reinforcement. Journal of Experimental Child Psychology, 1965,2, 205-2 18. Lewis, M. Probability learning in young children: The binary choice paradigm. Journal of Genetic Psychology, 1966, 108,43-48. Lewis, M., & Richman, A. Social encounters and their effect on subsequent social reinforcement. Journal of Abnormal and Social Psychology, 1964,69, 253-257. Lewis, M., Wall, A. M., & Aronfreed, J. Developmental change in the relative values of social and nonsocial reinforcement. Journal-of Experimental Psychology, 1963, 66, 133- 137. Lipsitt, L. P. Simultaneous and successive discrimination learning in children. Child Development, 1961,32,337-348. Little, K. B., Brackbill, Y.,Isaacs, R. B., & Smelkinson, N. A further test of a general utility model for probability learning. Journal of Experimental Psychology. 1963, 66, 107- 108. McCullers, J. C., & Stevenson, H. W. Effects of verbal reinforcement in a probability learning situation. Psychological Reports, 1960, 7 , 439-445. Messick, S. J., & Solley, G. M. Probability learning in children: Some exploratory studies. Journal of Genetic Psychology, 1957,90,23-32. Metzger, R. Probability learning in children and aments. American Journal of Mental DeJiciency, 1960,64, 869-874. Miller, G. A., & Frick, F. C. Statistical behavioristics and sequences of responses. Psychological Review, 1949.56.3 1 1-324.

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Neimark, E. D. Effects of type of nonreinforcement and number of alternative responses in two verbal conditioning situations. Journal of Experimental Psychology, 1956, 52, 209-220. Odom, R. D. Children’s probability learning as a function of the cross-sex effect. Psychonomic Science, I966,4, 305-306. Odom, R. D. Problem-solving strategies as a function of age and socioeconomic level. Child Development, 1967,38, 747-752. Odom, R. D., & Coon, R. C. The development of hypothesis testing. Journal of Experimental Child Psychology, 1966.4, 285-29 1. Offenbach, S. I. Studies of children’s probability learning behavior: I. Effect of reward and punishment at two age levels. Child Development, t964,35, 709-7 15. Offenbach, S. I. Studies of children’s probability learning behavior: 11. Effect of method and event frequency at two age levels. Child Development, 1965.36,95 1-962. Piaget, J. Une expkrience sur la psychologie du hasard chez I’enfant: le tirage au sort des couples. Acta Psychologica, 1950, I , 323-336. Rabinowitz, F. M., & Cantor, G. N. Children’s stimulus alternation, response repetition, and circular behavior as a function of age and stimulus conditions. Child Development, 1967,38,661-672. Rieber, M. Response alternation in children under different schedules of reinforcement. Psychonomic Science, 1966.4, 145- 150. Rosenhan, D. L. Effects of social class and race on responsiveness to approval and disapproval. Journal of Personality and Social Psychology, 1966.4, 253-259. ROSS,B. N. Probability concepts in deaf and hearing children. Child Development. 1966, 37,9 17-927. Schultz, D. P. Spontaneous alternation behavior in humans: Implications for psychological research. Psychological Bulletin, 1964, 62, 394-400. Schusterman, R. J. The use of strategies in two-choice behavior of children and chimpanzees. Journal of Comparative and Physiological Psychology, 1963,56,96- 100. Schusterman, R. J. Strategies of normal and mentally retarded children under conditions of uncertain outcome. American Journal of Mental Dejciency, 1964, 69,66-75. Siegel, S., & Andrews, J. M. Magnitude of reinforcement and choice behavior in children. Journal of Experimental Psychology, 1962,63,337-341. Skinner, B. F. The processes involved in the repeated guessing of alternatives. Journal of Experimental Psychology, 1942,30,495-503. Spiker, C. C., & Lubker, B. J. The relative difficulty of the successive and simultaneous discrimination problems. Child Development, 1965, 36, 109 1 - 1101. Stevenson, H. W., & Hoving, K. L. Probability learning as a function of age and incentive. Journal of Experimental Child Psychology, 1964, I, 64-70. Stevenson, H. W., & Odom, R. D. Children’s behavior in a probabilistic situation. Journal of Experimental Psychology, 1964,68, 260-268. Stevenson, H. W., & Weir, M. W. Variables affecting children’s performance in a probability learning task. Journal of Experimental Psychology, 1959,57,403-4 12. Stevenson, H. W., & Weir, M. W. The role of age and verbalization in probability learning. American Journal of Psychology, 1963,76, 299-305. Stevenson, H. W., & Zigler, E. F. Probability learning in children. Journal of Experimental Psychology, 1958, 56, 185- 192. Tolman, E. C. Purpose and cognition: The determiners of animal learning. Psychological Review, 1925,32,285-297. Tune, G . S. A brief survey of variables that influence random-generation. Perceptual and Motor Skills, 1964, 18,705-710. (a)

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Tune, G. S. Response preferences: A review of some relevant literature. Psychological Bulletin, 1964, 61, 286-302. (b) Walker, E. L. Action decrement and its relation to learning. Psychological Review, 1958, 65, 129-142. Weir, M. W. Effects of age and instructions on children’s probability learning. Child Development, 1962,33,729-735. Weir, M. W. Developmental changes in problem-solving strategies. Psychological Review, 1964.71.473-490.

Weir, M. W. Age and memory as factors in problem solving. Journal of Experimental Psychology, 1967,73,78-84. Weir, M. W. Memory and problem solving: A failure to replicate. Journal of Experimental Psychology, 1968,78, 166- 168. Weir, M. W., & Gruen, G. E. Role of incentive level, number of choices, and type of task in children’s probability learning. Journal of Experimental Child Psychology, 1965, 2, 121-134.

Wingfield, R. C. A study in alternation using children on a two-way maze. Journal of Comparative Psychology, I938,25,439-443. Wingfield, R. C. Some factors influencing spontaneous alternation in human subjects. Journal of Comparative Psychology, 1943,35, 237-243. Wingfield, R. C., & Dennis, W. The dependence of the rat’s choice of pathways upon the length of the daily trial series. Journal of comparative Psychology, 1934, 18, 135-147. Yost, P. A., Siegel, A. E., & Andrews, J. M. Nonverbal probability judgments by young children. Child Development, 1962,33, 769-780.

Author Index Numbers in italics refer to the pages on which the complete references are listed.

A Adams, G., 86,112 Adams, J. A,, 194,208,209 Alexander, H. M., 160, 174 Ambrose, J. A., 155, 172 Ames, E. W., 122, 143, 173, 178 Andrews, J. M., 215, 238,248, 249,253, 254 Angulo y Gonzalez, A. W.,6.9, 1 1, 12,34, 43, 45,SI Anokhin, P. K., 7,51 Antonitis, J. J., 161, 177 Apgar, V., 67, 11 I Arasteh, J. D., 170, 172 Arnold, H., 81, 113 Arnoult, M. D., 122, 127, 173,247, 249, 251 Aronfreed, J., 222, 239, 240,252 Arsenian, J. M., 152, 172 Arshavskiy, I. A., 35,51 Artom, G . , 4,52 Atkinson, R. C., 214,215,250 Attneave, F., 122, 127, 172, I73 Austin, M. F., 6, 57

B Badgley, C. E., 35,51 Balaban, M., 7, 9,44,45,53 Banker, B. Q., 35,52 Barclay, A., 2 18,223, 242, 243, 244,252 Barcroft, J., 6, 10, 38, 42, 45, 51 Barnes, G . W., 161, 173 Barnett, S.A., 142, 173 Barron, D. H., 6, 10, 38, 42, 45, 47,51

Bartels, B., 99, 106, 114 Bartoshuk, A. K., 80, 82,94,95,97, 112, 143, 173 Bauer, J. A., Jr., 33,53 Baumeister, A. A., 246, 251 Beach, D. H., 182,209 Beach, F. A., 120, 142,173 Beadle, K. R.,81, 94,112 Becker, R. F., 4,5, I I , 57 Beebe, H., 95,113 Beintema, D. J., 88, 116 BBlanger, D., 60, 115 Bellairs, A. d’A., 9,44, 45,54 Benjamin, L. S., 77, 112 Bennett, E. L., 33,55 Bennett, S., 81, 116 Berg, K. M., 76, 79, 92, 99, 100, 112 Berg, W. K., 63, 64, 65, 76, 79, 92, 99, 100, 112,113 Berlyne, D. E., 61, 112, 120, 121, 122, 123, 126, 131, 134, 135, 138, 139, 140, 151, 155, 156, 157, 158, 159, 160, 168, 171,173 Bernbach, H. A., 198,209 Bernuth,H.v.,97,114, 143,176,177 Bever, J., 63,116 Bickman, L., 80, 87,88, 116 Bindra, D., 156, I73 Birns, B. M.,80, 87, 88, I12 Bisett, B., 238,251 Black, A. H., 89,112 Blank, M., 80, 87, 88, 112 Blazek, N. C., 145, 160,176 Boat, B. M., 201,209 Bodian, D., 5,9,34, 36,45,46,51 Bogartz, R. S., 233,247,250,251 255

256

Author Index

Bolaffio, M., 4,52 Bot, A. P. C., 44,52 Bower, G. H., 214,215,250 Boyd, E., 52 Boyd, J. D., 35,53 Brackbill, Y., 86, 96, 112, 227, 237,251, 252 Brennan, W. M., 122,173 Bridger, W. H., 76,80,81,87,88,89,93, 112, 143,173 Bronson,G. W., 153, 154, 173, 174 Broverman, D. M., 170,174 Brown, W. L., 145, 174 Bruner, J. S . , 189,209 Brunswik, E., 215, 226, 227, 251 Bryant, S. V., 9,44,45,54 Buchwald, A. M., 63.82, 113 Burgers, J. M., 159, 174 Butler, R. A., 120, 156, 160, 161, 174

C Campbell, D., 153, 174 Campbell, H., 91, 114 Cannizzo, S . R., 182,210 Cantor, G. N., 91, 115, 120, 121, 123, 144, 145,174,178,247,253 Cantor, J. H., 145, 174 Carmichael, L., 3, 6,43,52 Carr, R. M., 145, 174 Caviness, J. A., 148, 179 Chase, H., 69, 82, 88, 89, 90, 112 Chase, H. H., 69,82,85,88,89,90,107, 112,114 Chase, W. G., 64,66,67, 77,112 Chinsky, J. M., 182, 209 Chun, B. J., 76, 81, 82, 83, 88,94, 95, 96, 113 Clapp, W. F., 124, 135, 137,174 Clifton, C., Jr., 201, 209 Clifton, R. K., 63, 64, 69, 70, 73, 76, 78, 79, 80, 82, 83, 84, 85, 86, 88, 92, 99, 107, 108, 109, 112, 113 Coates, B., 198, 20 I , 209 Coghill, G. E., 2, 3, 5 , 9, 12, 43, 52 Cohen, L. B., 218, 223, 224,242, 243, 244, 246,247,249,252 Collard, R. R., 146, 174 Conel, J. L., 96, 113

Coon, R. C., 234,249,250,253 Corner, M. A., 44,52 Coronios, J. D., 6, 9,45,52 Corsini, D. A., 182,209 Cotton, J. W., 228,251 Coulombre, A. J., 35, 52 Cox, F. N., 153, 174 Craft, M., 67, 113 Craig, G. J., 224, 251 Craig, J. G., 198, 211 Crandall, V. J., 223,232,249,251 Craw, M. A., 126, 140,173 Croll, W. L., 247,251 Crothers, E. J., 214,215,250 Crowell, D. H., 76, 81, 82, 83, 86, 88, 92, 94, 95, 96, 107,112, 113 Cuajunco, F., 48,52

D Daehler, M. W., 182,209 Daniel, R. S., 9, 56 Das, J. P., 216, 237, 239,251 Davies, C. M., 249,251 Davis, C. M., 76, 81, 82, 83, 88, 94, 95, 96, 113 Davis, M. E., 33,52 Davis, R. C., 63, 82, I13 Day, H., 171, 174 Dember, W. N., 124, 133, 139,174, 175, 214,247,251 Dennis, W., 246, 254 Derks, P. L., 223, 224, 235, 240, 243, 244, 246,249,251 Derr, J. E., 34,56 Desmond, M. M., 81,113, 117 Diamond, M. C., 33,52,56 DiCara, L. V., 89, 115 Dillman, A., 157, 180 240, 251 Dorwart, W., Doyle, G. A., 161, 178 Drachman, D. B., 35,52 Druger, R., 95,98, 116

E Earl, R. W.,124, 133, 139, 174, 175, 247, 25 I Eichorn, D. H., 124, 135, 137,174

Author Index

Eisenberg, R. B., 97, 113 Eisenman, R., 137, 139, 140, 175 Elligson, R. J., 96, 113 Ellis, N . C., 247, 249, 251 Emde, R. N., 155, 178 Emerson, P. E., 155, 179 Engen, T., 143, 175 Ernhart, C. B., 67, I13 Estes, W. K., 214,251 Ezerman, R.,240, 251

F Fantz, R. L.,97, 113, 122, 143, 151, 175 Faw, T. T., 157,175 Fish, M. W., 42, 57 Fiske, D. W., 124, 175 Fitzgerald, J. E., 4, 7, 9, 10, 12, 13, 16, 33, 34.4 I , 42,45,47,52, 57 Flavell, J. H., 182, 199, 203,209, 210, 211 Fourment, A., 33,56 Fowler, H., 120, 155, 159, 160, 161,175 Franklin, R. R.,81, 113. 117 Frankmann, R.W., 63,82,113 Fraser, D. C., 145, 175 Freedman, D. G., 155, 175 Frick, F. C., 226,252 Friedlander, B. Z., 161, 175, 177 Froeschels, E., 107, 113

G Gardner, R.A., 228,251 Gasser, R. F., 17, 52 Gejuoy, 1. R.,214, 223, 246,251 Gibson, E. J., 107, 113 Gibson, J. J., 107, 113, 148, 179 Gilman, A., I 1,52 Gilmore, J. B., 157, 175 Glanzer, M., 160, 175, 247, 248, 251 Glasshagle, E. E., 6, 43, 45, 5 7 Glickman, S . E., 142, 175 Goldberg, S., 99, 106, 114, 145, 170, 175, 177,248,252 Golubewa, E. L., 4, 7, 22, 52 Goodman, L. S., 11,52 Goodnow, J. J., 230, 232,233,252 Goodrick, C. L., 12i, 156,175 Goodwin, K., 223, 224, 225, 226, 227, 228, 229,235,252

257

Gottlieb, G., 3,9, 33,42,43,45, 52,53 Goulet, L. R.,218, 223, 240, 242, 243, 244,245,246, 252 Goy, R.W., 170, 175 Graham, F. K., 63,64,65,66, 67,69, 70, 73, 76, 77.78.79, 80, 82, 83, 84, 85, 86, 88, 92, 99, 100, 104, 105, 107, 108, 112,113,114 Grastyin, E., 63, 113 Gratch, G., 198,209, 242, 252 Gray, M. L., 82, 86, 88, 92, 107, 112, 113 Greenfield, P. M., 189, 209 Griffin, A. M., 6, 9,42,43,45,57 Gruen, G. E., 216,217,222,227,228,229, 230,237,238,239,252,254 Guilford, J. P., 170, 175 Gullickson, G. R.,64, 76, 115

H Hagen, J. W., 197, 198, 199, 202, 203,209, 210 Halliday, M. S., 155, 175 Halwes, T. G., 182, 203, 210 Hamburg, D. A., 170, 176 Hamburger, V., 3,7, 9, 30, 35,43,44,45, 47,53 Hamilton, W. J., 35, 53, 159, 177 Harlow, H. F., 145, 146, 160, 161, 174, 176, I77 Harlow, M. K., 145, 176 Harris, L., 147, 176 Harrison, R.G., 3 I , 53 Hartup, W. W., 198, 201,209 Hatton, H. M., 69,70,76, 79, 82, 84.85, 86, 88, 92, 101, 102, 103, 104, 106, 107, 108, 109,112,113 Hayes, J. R., 159, 176 Haynes, H., 134, 176 Haywood, H. C., 156,176 Headrick, M. W., 67,113 Hebb, D. O., 156,176 Hegion, A. G., 199, 211 Held, R.,33,53, 134, 176 Henker, B. A., 91,114 Hen-Tov, A., 91, 114 Hershenson, M., 122, 130, I76 Hewer, E. E., 48,53 Higgins, W. H., 156, 179

258

Author Index

Hill, R. M., 81, 113, 117 Hirota, T., 156, 157, 173 His, W., 34, 53 Hnatiow, M.,82, 114 Hoats, D. L., 123, 137,176 Hogg, I. D., 9, 41.48, 53 Holt, B. G., 123, 140, 179 Hooker, D., 3, 4, 9, 10, 11, 12, 14, 16, 17, 18, 19,20,21, 22,26,27,28,29, 31, 33, 34, 35, 37, 38,41, 42,43,45,46, 53,54 H0rd.D. J., 76, 99, 102, 113, 143, 177 Horowitz. A. B., 182, 209 Hoving, K. L., 217, 238, 239, 253 Hrbek, A., 96,114 Hrbkova, M.,96,114 Hubel, D. H., 97,114 Hughes, A., 9,44,45,54 Hull, C. L., 247,252 Humphrey, T., 6, 9, 10, 11, 12, 13, 15, 16, 17,18,19,20,21,22,23,26, 27,28, 29,31, 34, 35, 36,40,41,42,43,47, 48,54 Humphreys, L. G., 215,252 Hunt,J. McV., 151, 152,176 Hunt, W.A,, 94, 114 Hutt,C., 97, 114, 126, 135, 136, 141, 143, 146, 147, 149, 157, 161, 164, 165, 167, 168, 170,176,177 Hutt, S. J., 97, 114, 143, 157, 168, 177 Huttenlocher, J., 76, I I 7

I Isaacs, R. B., 227,252

J Jackson, J. C., 94, 103, 104, 105, 114 Jacobs, M. J., 40,55 Jacobson, M., 3, 30,55 Jameson, J., 80, 87, 88, 116 Jeffrey, W. E., 218, 223, 224,242,243, 244,246,247,249,252 Jensen, A. R., 198,203,210 Johnson, L. E., 76.99, 102,113, 143,177 Jones, M. H., 221,222,232,249,252

K Kagan, J., 91, 114, 115, 132, 134, 144, 161, 170, 171,177 Kalafat, J . , 91, 114, 134, 144, 177 Kantowitz, S., 67, 104, 105, 114 Kappy, M. S., 237,251 Karmos, G., 63,113 Kaye, H., 143, 175 Keen, R. K., 82,85, 88, 107, 114 Keeney, T. J., 182,210 Kellaway, R., 222, 232, 249, 251 Kellenyi, L., 63, 113 Kendler, H. H., 194, 210 Kendler, T. S., 182, 194,210 Kessen, M. L., 128, 129, 135, 178, 223, 232,249,252 Kessen, W., 122, 127, 128, 129, 130, 134, 135,176, 178,179,223,232,249,252 Khachaturian, Z., 95, 98, 116 Kiang, N. Y. S., 97,114 Kimura, D., 170,177 King, T. G., 34,56 Kingsbury, B. F., 40,55 Kingsley, P. R., 198, 199,202, 203,209, 210 Kish,G. B., 111,114, 161, 173, 177 Klaiber, E. L., 170, I74 Kobayashi, Y.,170,174 Koenig, I. D., 156, 157,173 Kogan, H., 170,180 Koltsova, M. M., 96, 112 Korn, J. H., 66, 114 Kotses, H., 63, 116 Krech, D., 33,55 Kuhlman, C. K., 197,210 7, 9, 39, 43, 45, 53, 55 KUO,Z.-Y.,

L Lacey, J. I., 60,63,70, 74,114 Lampl, E. E., 155,179 Landis, C., 94, I14 Lang, P.J., 82,114 Langley, A. L., 43,55 Lawick-Goodall, J. V.,142,177 Lenard,H.G.,96,97,:14, 143,176, 177 Lester, D., 155,177

259

Author Index

Leuba, C., 124, 161,177 Levine, J., 91, 114 Lewis, J. L., 126, 140, 173 Lewis, M., 91, 99, 106, 114, 134, 144, 145, 161, 170, 171, 175, 177, 216, 222, 223, 239, 240,251,252 Licklider, J. C. R., 96, 114 Lieberman, J. N., 170, 177 Lind, J., 39,56 Lindner, B., 33, 52 Lipsitt, L. P., 143, 175, 217, 252 Lipton, E. L.,70,78,80, 88,91, 110, 114, 115. 116, 117 Little, K. B., 227, 252 Lituchy, S., 80, 87, 88, 116 Liverant, S., 221, 222, 232, 249,252 Lodah1,T. M., 161, 178 Lubin, A., 76, 99, 102, 113 Lubker, B. J., 217,253 Ludwig, H., 69, 115 Lunde, D. T., 170, 176 Luria, A. R., 182, 210 Lynch, J. J., 65, 115 Lynn, R., 61,93, 115

M McCall, R. B.,91, 115, 132, 134, 177 McCarthy, J. J., 161, 175 McClearn, G. E., 145, 160, 161,176 Maccoby, E. E., 170, 171, 177, 182, 210 McCullers, J. C., 240, 243,252 McDonald, D. G., 143,177 McGrew, P. L., 135, 136, 176 McReynolds, P., 155,177 Maddi, S. R.,124, 175 Magoun, H. W., 36,55,61,115 Mall, F. P., 55 Malmo, R. B., 60,115 Mandler, G., 206,210 Marais, F. N., 142, 177 Marler, P. J., 159, I77 Martin, C. J., 194, 196, 198, 203,210 Martin, J., 63, 113 Mavrinskaya, L. F., 4,55 May, R. B.,125, 134, 177 Mendel, G., 147,177 Messick, S.J., 218, 222,252 Metzger, R.,223,252

Meyer, D. R.,145,176 Meyers, W. J., 64, 76, 91, 92, 109, 112, 115, 144, 178 Milgram. N. A., 198, 204, 210 Miller, G. A., 226, 252 Miller, M. B., 123, 137, 176 Miller, N. E., 89, 115, 160,178 Minear, W. L., 6, 57 Minkowski, M., 3.4, 5,42,43,45,55 Moely, B. E., 182, 198, 203, 210 Moffett, A., 143, 178 Moffitt, A. R., 76, 91, 97,115 Montgomery, K. C., 160, 178 Moon, L. E., 161, 178 Moore, R. W., 122, 173 Morgan, G. A., 155,178 Moruzzi, G., 61, 115 Moss, H., 170, 178 Mossman, H. W., 35,53 Moyer, K. E., 66,114 Muller-Schwarze, D., 169, 178 Munsinger, H., 122, 127, 128, 129, 130, 134, 135, 176, 178 Muntjewerff, W. J., 97, 114, 143, 177 Murphy, W. F., 43,55 Murray, D. J., 197, 202, 210 Myers, A. K., 160, 178 Myers, J. L., 224,251

N Neimark, E. D., 228, 253 Newton, J. E. O., 65, 115 Nilsson, L., 43,55 Noble, C. E., 196, 211 Nunnally, J. C., 157,175

0 Obrist, P. A., 89, 115 Odom, R. D., 216,217,234,241,242,249, 250,253 O’Donnell, J. E., 6, 43,45,57 Offenbach, S. I., 216, 217, 228, 237,239, 253 Ogilvie, J. C., 171, 173 Olson, F. A., 182,203,210 Olson, R. E., 69, I15

260

Author Index

Oppenheim, R., 7,9,43,44,45,53 Ordy, J. M., 157,180 Orr, D. W.,6, 9, 43,45,52,57

P Paclisanu, M., 223,224, 235, 240, 243, 244,246,249,251 Panda, K. C., 216,237, 239,251 Pap, L. F., 81, 117 Paradise, N., 139, 175 Parham,L.C.C., 140, 171,173 Parry, M. P., 147, 148, 179 Partanen, T., 39,56 Patten, B. M., 35,55 Patton, H. D., 36,56 Payne, B., 134,178 Peake, W. T., 97,114 Pederson, D. R., 247,250,251 Perez-Cruet, J., 65, 115 Pettigrew, T. F., 232, 233,252 Piaget, J., 206,210, 248,253 Pick, A. D., 182, 203, 209 Plumb, R., 81,113 Polak, P. R., 155, 178 Polikanina, R. I., 93, 106, 107, 115 Posner, M. I., 194,210 Potter, E. L., 35, 52 Prechtl, H. F. R., 43,55, 88, 116, 143, 176, 177 Prestige, M. D., 44,54 Preyer, W.,35,55 Pritchard, J. A., 35,55 Probatova, L. E., 93, 106, 115

R Rabinowitz, F. M., 241, 253 Ranken, H. B., 191, 196, 210 Ransom, S. W.,6 , 5 5 Rappaport, J., 137, 175 Raskin, D. C.,63, 116 Rausch, M., 145,177 Raymond, A., 33,52 RechtschafTen, A., 228, 251 Reese, H. W.,182,210 Reiser, M., 76, 80,81,89,93, 112 Reynolds, S. R. M., 8,34,55

Rheingold, H. L., 154, 161, 178 Rhines, R., 36, 55 Ricciuti, H. N., 155,178 Richman, A., 240,252 Richmond, J. B., 70,73, 80, 88,89, 91, 109, 110,114, 115, 116, 117 Rieber, M., 218,223,238,242,243,251, 253 Riesen, A. H., 95,116 Robinson, R., 134, 178 Rohwer, W. D., Jr., 198, 203, 210 Rosenbaum, M. E., 197,210 Rosenhan, D. L., 216, 240, 251, 253 Rosenthal, M. K., 153, 178 Rosenzweig, M. R., 33,55 Ross, B. N., 248,249,250,253 Routtenberg, A,, 61, 109, 116 Royer, F. L., 63, I16 Ruch, T. C., 36,56 Rudolph, A. J., 81, 117 Rueping, R. R., 146,177 Rump, E. E., 135.178 Rush,J. B., 81, 117 Ryan, S . M., 199,211

S Saayman, G., 143, 178 Sackett, G. P., 134, 179 Salapatek, P., 134, 179 Salapatek, P. H., 126, 140, 173 Sameroff, A., 97, 107,116 Schachter, J., 73, 78,80, 81, 87, 88,95, 98, 116,117 Schachter, J. S., 80,87, 88, 116 Schaf€er,H. R., 147, 148, 155,179 Scharpenberg, L. G., 47,56 Scheibel, A. B., 85, 96, 116 Scheibel, M. E., 85,96, 116 Scherrer, J., 33,56 Schiff, W.,148. 179 Schneirla, T. C., 61, 116 Schulman, C. A.. 106,116 Schultz, D. P., 214, 253 Schustennan, R. J., 223,233, 243,250, 253 Sheldon, A. B., 152, 156, I79 Sheldon, M. H., 156,179 Sherrington, C. S., 40, 56 Shillitoe, E. E., 142, 179

26 1

Author Index

Shulejkina, K. V., 4, 7, 22, 52 Siebert, W. M., 97,114 Siegel, A. E., 2 15, 248, 249, 254 Siegel, S., 238, 253 Silverman, I. W., 198, 211 Skinner, B. F., 247, 253 Smelkinson, N., 227, 252 Smith, D. B. D., 64, 117 Smith, K., 88, 117 Smith, K. U., 9,56 Smith, R. K.,196, 211 Smock, C. D., 123, 140,179 Soforenko, A. Z., 161,175 Sokolov, E. N., 61,62,63,96, 98.99.117, 140,179 Solley, G. M., 218, 222, 252 Solomon, D., 222, 232, 249, 251 Sontag, L. W., 107,117 Spaulding, S. J., 91, 114 Spencer, W. A., 163,179 Spiker, C. C., 217,253 Spinner, N., 156, 173 Spitz, H. H., 123, 137, 176 Spitz, R. A., 155, 178, 179 Sroges, R. W., 142, 175 Stanley, W. C., 161, 178 Starr, R. H., 237,251 Steffek, A. J., 34,56 Steinschneider, A., 70,73,78,80, 88.89, 90,91,109, 110,114,115,116,117 Stenson, H. H., 134,179 Stevenson, H.W., 217,219,220,221,222, 230, 231, 234, 238, 239, 240, 241, 242, 243,252,253 Strassman, P., 3,49,56 Strawbridge, P. J., 64,117 Streeter, G. L., 12, 56 Stretch, R., 157,179 Sutterer, J. A., 8 9 , l I5 Swenson, E. A., 6 , 5 6 Symmes, D., 161,179 Sztkely, G., 3 1, 56 SzentQothai, J., 31, 56

T Taylor, D. C., 170,179 Tennes, K. H., 155,179 Terwilliger, R. F., 134,179

Thomas,H., 122,131,179 Thompson, R. F., 163,179 Thompson, W. R., 156,179 Thorpe, W. H., 159,180 Thurston, D., 67,113 Tobin, M.. 73, 78, 87, 95, 98, 116, 117 Tolman, E. C., 246,253 Tomnce, E. P., 170,180 Towe, A. L., 36,56 Tracy, H. C., 43,56 Tuge, H., 9,45,56 Tune, G. S., 214,253,254

U Underwood, B. J., 195,211

V Vainstein, I. I., 4,7,22,52 Valannt, E., 39,56 Vallbona,C.,81,113,117 Vereczkey, L.,63,113 Vitz, P. C., 133, 134,180 Vogel, W., 170,174 Vuorenkoski, V., 39,56 Vygotsky, L. S., 184, 196,211

W Wachs, T. D., 156,176 Walberg, F., 36,56 Walker, B. E., 139,180 Walker, E. L., 139,180,247,254 Wall, A.M., 222,239,240,252 Wallach, M. A., 170,180 Wasz-Hijckert, O., 39,56 Watts,J.,81,113 Waugh, M., 35,53 Webb, R.A,, 89,115 Weir,M. W., 130,178,215,216,217,220, 221,222,223,224,225,226,227,228, 229,230,23 1,234,235,236,237,238, 239,240,243,244,246,250,252,253, 254 Weiss, P., 7,30,3 1,56 Weiss, T. F., 97,114 Welker, W. I., 121,139, 146,159,180 Wenger, E., 7,9,43,44,45,53

262

Author lndex

Westcott, M. R., 76, 11 7 Wolff, P. H., 88,99,117 White, 8. L., 134, 176 Wolin, L. R., 157,180 Wickelgren, L. W.,134,180 Woodbury, J. S., 36.56 Wiederhold, M. L., 97,114 Wynns, F. C.,182,209 Wiesel, T. N., 97, 114 Wilder, J., 74,117 Y Williams,J.D.,81,II6 Williams, T. A., 73,78,80,8 1,87,88,95, Yanase, J., 3.49.57 98,116,117 Yost, P. A., 21 5,248,249,254 Windle,W.F.,3,4,5,6,7,9,10,ll,l2,13, Youngstrom, K. A., 45,57 16,33,34,41,42,43,45,47,52,55,56, 57 Wingfield, R. C., 246,254 Z Winters, J. J., Jr., 214,223,246, 251 Wohlwill, J. F., 203,209 Zigler, E. F., 2 17, 2 I9,220,22 I , 234,253

Subject Index A

development of, see under Fetal activity postnatal, relation to fetal activity, see Fetal activity Behavioral state, heart rate response and, 87-91,98-105 Bodily movement, heart rate response and, 87-91 Boredom, specific and diversive activities and, 159-161

Activity, fetal, see Fetal activity Adult, arousal systems and, 62-67 Age-changes, probability learning and, 234-237 Alternation behavior, 246-248 Anesthetics, behavioral development and, 10-12 Anoxia, behavioral development and, 10-12 Approach-avoidance conflict, see under Exploration Arousal systems, 59-1 17 evoked heart rate response and, 78-108 factors affecting developmental shift and, 93-108 in newborn, 79-91 in older infants, 9 1-93 experimental procedure and, 67-78 heart rate response measurement and, 69-78 laboratory arrangements and, 68-69 subjects and, 67-68 OR-DR differentiation in adult subjects and, 62-67 Asphyxia, behavioral development and, 10-12 Attention, complexity as determinant of, 121-138 comparison of variables of complexity and, 135-138 multidimensional complexity and, 122-126 unidimensional complexity and, 127- 135

Drugs, behavioral development and, 10- 12

B

E

Behavior, choice. see Choice behavior

C Choice behavior, 2 13-254 alternation and, 246-248 development of probability concept and, 248-249 guessing and, 242-246 hide-and-seek and, 24 1-242 probability learning and, 214-240 definitions and, 214-216 descriptive developmental changes in, 222-226 historical aspects and, 218-222 methods and, 2 16-2 18 variables influencing, 226-240 Clustering, mediated memory and, 186- 189 Complexity, see under Exploration Conflict, approach-avoidance, see under Exploration Curiosity, specific and diversive activities and, 159-161

D

Environment, novelty as determinant of exploration and, 15 1 - 155

263

Subject Index

264

Experience, postnatal, heart rate response and, 105-108 Exploration, 119- 180 complexity as determinant of, 12 1- 138 comparison of variables of complexity and, 135-138 multidimensional complexity and, 122-126

unidimensional complexity and,

period of widespread reactions and, 12-16

postnatal repetition of fetal reflex activity sequences and, 41 -42 suppression of activity and, 36-40 theories on development of behavior and, 4-7

local reflex concept and, 6 total pattern concept and, 5-6

127-135

G

novelty as determinant of, 138-158 approach-avoidance conflict and, 157-158

Guessing behavior, 242-246

definitions of novelty and, 140-141 fear of novelty and, 155-157 habituation to visual novelty and, 144-145

novelty in a biological context and, 141-143

separation of novelty and complexity variables and, 139-140 sources of novelty and, 145-155 two-dimensional novelty and, 143- 144 specific and diversive activities and,

H Habituation, novelty as determinant of exploration and, 144- 145 Heart rate, see under Arousal systems Hide-and-seek behavior, 24 1-242

I Incentive, probability learning and, 237-240

159- 17 1

characteristics of, 167- 171 curiosity and boredom theories and, 159- 161

investigation and play and, 16 1 - 167

Infant, arousal systems and, see Arousal systems Inhibition, fetal activity and, 36-40 Instructions, probability learning and, 229-230

F Fear, novelty and, 155-157 Fetal activity, 1-57 historical background and, 3-4 integration and the development of behavior and, 46-49 methods of investigating behavioral development and, 7- 12 effects of anoxia, asphyxia, anesthetics, narcotics and other drugs and, 10-12

recording methods and, 8-9 types of stimuli and, 9- 10 spontaneous, 43-46 stimulation other than tactile and, 41 -43 tactile stimulation and, 12-41 function of fetal reflexes and, 30-35 localized reflex activity and, 16-30

Investigation, specific and diversive activities and, 161-167

Learning, probability, see under Choice behavior

M Mediated memory, 18 1-2 1 1 clustering as mediating activity and, 186- 189

nature of mnemonic mediation and, 193-197

nonverbal mediators and, 189- 191 production and mediational deficiencies and, 198-207 verbal production deficiency and, 182-184

265

Subject Index

verbal rehearsal and, 184- 186 verbal versus nonverbal mediating activity and, 19 1 - 193 Memory, mediated, see Mediated memory Mnemonic mediation, see under Mediated memory

N Narcotics, behavioral development and, 10-12 Newborn, evoked heart rate response in, 79-91 Novelty, see under Exploration

P Penalty, probability learning and, 239 Play, specific and diversive activities and, 161- 167 Postnatal experience, see Experience, postnatal Probability learning, see under Choice behavior Problem solving, see Choice behavior

R Reaction, widespread, tactile stimulation of fetuses and, 12- I6 Reflex, defense, arousal systems and, 62-67 function of in fetus, 30-35 local, 6, 16-30 orienting, arousal systems and, 62-67

Reflex sequences, fetal, postnatal repetition of, 4 1-42 Rehearsal, see under Mediated memory Reinforcement, partial, probability learning and, 226-227 social, probability learning and, 239-240 Response, heart rate, see under Arousal systems Response patterns, communality of, probability learning and, 240 Reward, tangible, probability learning and, 237-239

S Social reinforcement, probability learning and, 239-240 Stimulation, characteristics of, heart rate response and, 93-98 methods of investigating behavioral development and, 9-10 tactile, see under Fetal activity

T Transfer of training, probability learning and, 23 1-234

V Verbal mediation, see under Mediated memory Visual novelty, see under Exploration

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ERRATA ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR VOLUME 5

Edited by Hayne W. Reese and Lewis P. Lipsitt page 136, Fig. 2: The labels “Complex” and “Simple” should be reversed page 143,2nd paragraph, 3rd line: “newborn” should read “young”

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