Cognition, Vol. 2, No. 4

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Psychological reactivity to discrepant events: Support for the curvilinear hypothesis*

PHILIP R. ZELAZO J. ROY HOPKINS SANDRA JACOBSON JEROME KAGAN Harvard University Abstract 80 male and 60 female infants were observed under 5 a priori judged levels of discrepancy to assess whether sustained attention was linearly or curvilineariy related to degree of discrepancyfrom an experimentalstandard. Following habituation, 7&month-oldinfants were exposed to either the repetition of the standard, a minimal, first- or second-level moderate discrepancy, or a novel stimulus having no relation to the standard. The related stimuli, varying in elongation, were sphere, pear, club, and cylinder-shaped objects; the novelstimulus was a di_ffrent colored, tooth-like object. 80 infants observed the sphere as the standard and the cylinder as the second-level moderate discrepancy; 60 infants were exposed to the reverse order with the cylinder as the standard. The use of dcxerent stimuli at each discrepancy level controlled for spec$c stimulus effects. Habituation and recovery of responding were observed in an operant paradigm. Lever pressing, jixation, and vocalization increased most to the second-level moderate stimuli anddecreasedmost to thefamiliar andnovel objects: fretting was highest to the redundant stimuli and lowest to the moderate objects. There were no stimulus main eflects or The results support the hypothesis of a curvilinear relation between interactions. stimulus discrepancy and sustained attention, excitement, andpreference.

As attentional processes become more central in psychological theory the issue of environmental determinants of attention becomes a major theme for empirical inquiry. The traditional view of the relation between external event and recruitment of attention in infants and young children was phrased in absolute terms, and it was postulated that the attention-getting power of a specific event could be stated in terms of fixed * This research was supported by grant HD4299 from National Institute of Child Health and Human Development, USPHS; grant OCD-DB-174 from the Office of Child Development, and a grant from the Spencer Foundation, Chicago, Illinois. We thank C.

Super and J. Reiser for their suggestions and help during the early phases of this research. Requests for reprints should be sent to Philip R. Zelazo, Department of Psychology and Social Relations, Harvard University, Cambridge, Massachusetts 02138, U.S.A. Cognition 2(4),

pp. 385-393

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Philip R. Zelazo, J. Roy Hopkins, Sandra Jacobson and Jerome Kagan

qualities-degree of complexity or amount of contour, for example (Dember and Earl, 1957). That view has been amplified by a series of experiments indicating that the familiarity of an event is an important determinant of sustained attention (Fantz, 1964; Fantz and Nevis, 1967; McCall and Kagan, 1967; Lewis, 1969; McCall and Melson 1969; Kagan, 1970, 1971). However, this relativistic position - called the discrepancy hypothesis - has at least two alternative forms. The first states that the relation between degree of discrepancy from the organism’s internal abstract representation of the event and sustained attention to the event itself is linear (Saayman, Ames and Moffett, 1964; McCall and Kagan, 1970; Jeffrey and Cohen, 1971). The more different the stimulus is from the organisms’ prior experience, the more attention it will recruit. An alternative view posits a curvilinear function with an optimal degree of discrepancy recruiting maximal attention and with very familiar and very discrepant (or novel) events recruiting relatively less interest (Hebb, 1949; McCall and Kagan, 1967 ; McCall and Melson, 1969 ; Kagan, 1970, 1971; Super, Kagan, Morrison, Haith and Weiffenbach, 1972). Cohen and his associates (Cohen, 1973; Cohen, Gelber and Lazar, 1971) have wisely differentiated between events that produce an initial orientation and events that elicit sustained attention following the initial response. Sustained attention has not been adequately examined, in part because assimilation occurs too rapidly with the simple stimuli that have typically been used. Paradoxically, it is desirable to use simple stimuli in order to establish a single dimension of change and to estimate the distances between stimuli (c$ Thomas, 1971). Thus, a procedure was developed that allowed for the gradual exposure of relatively simple, a priori ordered stimuli, in effect, amplifying the transformation period. The operant habituation-dishabituation procedure used by Siqueland (1969) and the suggestion that operant responding for a visual reward may function in a manner analogous to other attentional measures (Zelazo, 1972) lead to the development of an operant procedure that permitted brief stimulus exposures. Consistent results for fixation, vocalization and additional measures such as operant responding and fretting can also strengthen the argument that the curvilinear discrepancy function observed in earlier studies reflects an underlying cognitive process and not simply individual response characteristics. Moreover, a curvilinear operant pattern would imply that a visual reward may derive its reinforcing effectiveness from the child’s level of schemata growth for that stimulus. The purpose of this paper, therefore, is to determine if multiple indices of attention, including an operant measure, are consistent with the linear or curvilinear forms of the discrepancy hypothesis when the transformation period is prolonged and a priori ordered stimuli are used.

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Method Subjects and design One hundred and forty normal Caucasian infants, 80 boys and 60 girls, were recruited from advertisements in a local newspaper and from birth records. Eighty-six children were excluded because of mechanical problems, failure to reach criterion or excessive fretting. All children were 73 months old (plus or minus 2 days) and 84 % were from college educated families; 45% of all parents had some post-graduate training. There were five discrepancy groups: No change, minimal change, two different levels of moderate change and a major change (or novel) group. A series variable was formed by reversing the four groups from no change to minimal to moderate change in order to distinguish the effect of discrepancy from the effects of specific stimuli. Thus, discrepancy groups, series and sex were independent variables with the standard and transformation periods (i.e., the means for the last two minutes of the standard and the first two minutes of the discrepant stimuli) as a repeated measure in the analysis of variance. Stimuli The five stimuli were approximately equal in volume and made of papier-mache. Figure 1 illustrates the sphere, pear-shaped form, club-shaped form, cylinder and irregular tooth-shaped objects. The first four objects were all red with 3 inch black stripes; the tooth-shaped object was green with no stripes. For the 80 infants tested in Series 1, the sphere was the standard to which they were habituated and the discrepant object that was presented following habituation was either the pear-shaped form (minimal discrepancy), the club or cylinder (first- and second-level moderate discrepancies) or the tooth (novel or major discrepancy). For the 60 infants seen in Series 2 the order of the red and black objects was reversed to control for specific stimulus effects. Hence the cylinder was the standard to which they were habituated and the discrepant object was either the club (minimal discrepancy), the pear or sphere (first- and second-level moderate discrepancies) or the tooth (novelty). The control subjects who received no change in object continued to see the sphere in Series 1 or the cylinder in Series 2. The stimuli were prepared with the aid of eleven adult judges who were shown the five objects simultaneously in random formation. They were asked to rank the objects according to degree of elongation using the sphere as the reference and to estimate the intervals between adjacent objects. The four related objects were restricted to the

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Philip R. Zelazo, J. Roy Hopkins, Sandra Jacobson and Jerome Kagan

Figure 1. The sphere, pear-shaped object, club-shaped object, cylinder and tooth-like object used as stimuli in the experiment.

range between 0 and 10; the novel object was allowed to vary from 0 and 100. Eight judges ordered the pear, club and cylinder as progressively more elongated from the sphere; the median scores were 3, 6, 10 and 0 respectively. The tooth-like object was judged as unrelated and assigned a median value of 20. Three of the judges placed the irregular object among the related objects because of its height. Procedure

Each baby was seated on his mother’s lap facing a 14-inch square window in front of a two-compartment box resembling a two-channel tachistoscope. Ambient illumination in the room was kept low and constant throughout testing. A bright yellow padded lever extended from beneath the window of the apparatus. A lever press lighted one compartment and provided a 2+ second view of the three dimensional object. All objects revolved on a turntable at 16 revolutions per minute in order to maximize the attention-eliciting properties of the stimuli. The standard stimulus was changed to the discrepant stimulus by closing a switch in the control room which caused the discrepancy chamber to light on the next lever press. The infant’s instrumental responses were automatically recorded on a polygraph.

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An observer watched the subject through a one-by-four inch window behind one of the chambers and recorded duration of lixation, vocalization and fretting on a button box linked to a polygraph. Responses were easily coded because the procedure permitted a clear, face-forward view of the infant. Fixation was scored only if the infant looked directly forward. All positive sounds were scored as vocalizations while ambiguous and negative sounds including crying were scored as frets. Interobserver reliabilities were calculated for five infants for each of these variables. Scores for two coders were compared for each 20-second period throughout each of these records. Observers were always blind with respect to experimental treatment and each other. Pearson product moment correlations for the four measures and the five pairs of infants were all above 0.90. Intercoder reliabilities for fixation and vocalization from a recent experiment in this laboratory were comparable : rs = 0.96 and 0.97 respectively (Zelazo, Kagan, and Hartmann, in press). Every 20 seconds the accumulated number of instrumental responses to occur accompanied by fixation of the stimulus during any portion of the 23 seconds of illumination (called reinforced instrumental responses) was tallied on-line from the automatic stimulus marking channel of a Grass polygraph. These calculations were immediately graphed and used to determine when each S had displayed criteria1 habituation and was ready for introduction of the discrepant stimulus. The following criteria for habituation were used: (a) Reinforced responses increased over base level, (b) reinforced responses following peak responding in two consecutive periods decreased below 50% of the mean of the previous two 20-second periods, (c) the standard period must have lasted at least three minutes from the child’s first reinforced response, and (d) the S must have had at least ten reinforced responses. When these criteria were reached the discrepant stimulus was illuminated. A final requirement was that the transformation period must have lasted a total of at least three minutes.

Results

The results revealed a main effect for the standard-transformation factor1 and a significant standard-transformation by group interaction for all four dependent variables. There were no series or sex main effects and only one third-order interaction for fixation time (group by sex by standard-transformation; F= 2.49, df = 4/120, pc.05) among the 60 statistical comparisons made for the four measures. The 1. The standard-transformation variable was used in the analyses rather than transformation scores alone because reliable differences oc-

curred among groups during the last minute of the standard.

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higher-order interaction revealed a clearer curvilinear pattern of recovery among groups for boys. The repeated finding of no difference for the series variable indicates the minor contribution of specific stimuli. Change scores were derived from the standard-transformation by groups interactions by subtracting the means for the standard from the means for the transformation for each discrepancy group and each dependent variable. Trend analyses were calculated for the change scores in the five discrepancy groups (combined over the nonsignificant series and sex variables) using coefficients computed for unequal intervals based on the adult judgments (Gaito, 1965). Table 1 shows the means for the standard-transformation by groups interaction and the derived mean change scores. Results for the trend analyses for each variable are also presented in Table 1. Table 1. Behavioral changes following presentations of discrepant objects Degree of discrepancy

Reinforced responses (minutes) Fixation time (seconds) Vocalizations (seconds) Fretting (seconds)

n

No change

Minimal

STd

STd

Trend analysis

First-level moderate

Secondlevel moderate

Novel

STd

STd

STd

Source

df

F

p9.03, p < .02. At the fifth series only, boys (as well as girls) had labelled adult-named referents significantly more frequently than adult-unnamed referents F (1,8) = 17.72, p < .Ol. Girls showed significantly more naming than boys for adult-named objects at the end of each series (F (1,8) >8.41, p < .02) and for adult-unnamed referents at series 5 (F (1,8)=201, p< .OOl). The interaction of children’s sex by adult naming was significant in the analyses of performance at the end ot series 2, 3, 4 and 5, (in each case 5.70