Spatial Cognition VI.. Learning, Reasoning, and Talking about Space, Spatial Cognition 2008

Lecture Notes in Artificial Intelligence Edited by R. Goebel, J. Siekmann, and W. Wahlster

Subseries of Lecture Notes in Computer Science

5248

Christian Freksa Nora S. Newcombe Peter Gärdenfors Stefan Wölfl (Eds.)

Spatial Cognition VI Learning, Reasoning, and Talking about Space International Conference Spatial Cognition 2008 Freiburg, Germany, September 15-19, 2008 Proceedings

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Series Editors Randy Goebel, University of Alberta, Edmonton, Canada Jörg Siekmann, University of Saarland, Saarbrücken, Germany Wolfgang Wahlster, DFKI and University of Saarland, Saarbrücken, Germany Volume Editors Christian Freksa SFB/TR 8 Spatial Cognition Universität Bremen, Bremen, Germany E-mail: [email protected] Nora S. Newcombe James H. Glackin Distinguished Faculty Fellow Temple University, Philadelphia, PA, USA E-mail: [email protected] Peter Gärdenfors Lund University Cognitive Science Lund, Sweden E-mail: [email protected] Stefan Wölfl Department of Computer Science University of Freiburg, Freiburg, Germany E-mail: woelfl@informatik.uni-freiburg.de

Library of Congress Control Number: 2008934601 CR Subject Classification (1998): H.2.8, I.2.10, H.3.1, K.4.2, B.5.1 LNCS Sublibrary: SL 7 – Artificial Intelligence ISSN ISBN-10 ISBN-13

0302-9743 3-540-87600-6 Springer Berlin Heidelberg New York 978-3-540-87600-7 Springer Berlin Heidelberg New York

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springer.com © Springer-Verlag Berlin Heidelberg 2008 Printed in Germany Typesetting: Camera-ready by author, data conversion by Scientific Publishing Services, Chennai, India Printed on acid-free paper SPIN: 12519798 06/3180 543210

Preface

This is the sixth volume in a series of books dedicated to basic research in spatial cognition. Spatial cognition research investigates relations between the physical spatial world, on the one hand, and the mental world of humans, animals, and artificial agents, on the other hand. Cognitive agents – natural or artificial – make use of spatial and temporal information about their environment and about their relation to the environment to move around, to behave intelligently, and to make adaptive decisions in the pursuit of their goals. More specifically, cognitive agents process various kinds of spatial knowledge for learning, reasoning, and talking about space. From a cognitive point of view, a central question is how our brains represent and process spatial information. When designing spatial representation systems, usability will be increased if the external and internal forms of representation are aligned as much as possible. A particularly interesting feature is that much of the internal representations of the meanings of words seem to have a spatial structure. This also holds when we are not talking about space as such. The spatiality of natural semantics will impose further requirements on the design of information systems. An elementary example is that “more” of something is often imagined as “higher” on a vertical dimension: consequently, a graphical information system that associates “more” with “down” will easily be misunderstood. Another example concerns similarity relations: features that are judged to be similar in meaning are best represented as spatially close in a graphical information system. In addition to the question of how this information is represented and used – which was the focus of the previous Spatial Cognition volumes – an important question is whether spatial abilities are innate (“hard wired”) or whether these abilities can be learned and trained. The hypothesis that spatial cognition is malleable, and hence that spatial learning can be fostered by effective technology and education, is based on recent evidence from multiple sources. Developmental research now indicates that cognitive growth is not simply the unfolding of a maturational program but instead involves considerable learning; new neuroscience research indicates substantial developmental plasticity; and cognitive and educational research has shown us significant effects of experience on spatial skill. Because an informed citizen in the 21st century must be fluent at processing spatial abstractions including graphs, diagrams, and other visualizations, research that reveals how to increase the level of spatial functioning in the population is vital. In addition, such research could lead to the reduction of gender and socioeconomic status differences in spatial functioning and thus have an important impact on social equity. We need to understand spatial learning and to use this knowledge to develop programs and technologies that will support the

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Preface

capability of all children and adolescents to develop the skills required to compete in an increasingly complex world. To answer these questions, we need to understand structures and mechanisms of abstraction and we must develop and test models that instantiate our insights into the cognitive mechanisms studied. Today, spatial cognition is an established research area that investigates a multitude of phenomena in a variety of domains on many different levels of abstraction involving a palette of disciplines with their specific methodologies. One of today’s challenges is to connect and relate these different research areas. In pursuit of this goal, the Transregional Collaborative Research Center SFB/TR 8 Spatial Cognition (Bremen and Freiburg) and the Spatial Intelligence and Learning Center (Philadelphia and Chicago) co-organized Spatial Cognition 2008 in the series of the biannual international Spatial Cognition conferences. This conference brought together researchers from both centers and from other spatial cognition research labs, from all over the world. This proceedings volume contains 27 papers that were selected for oral presentation at the conference in a thorough peer-review process to which 54 papers had been submitted; each paper was reviewed and commented on by at least three Program Committee members. Many high-quality contributions could not be accepted due to space limitations in the single-track conference program. The Program Chairs invited three prominent scientists to deliver keynote lectures at the Spatial Cognition 2008 conference: Heinrich H. B¨ ulthoff spoke on “Virtual Reality as a Valuable Research Tool for Investigating Different Aspects of Spatial Cognition”, Laura Carlson’s talk was about “On the ‘Whats’ and ‘Hows’ of ‘Where’: The Role of Salience in Spatial Descriptions”, and Dedre Gentner addressed the topic “Learning about space”. Abstracts of the keynote presentations are also printed in this volume. Spatial Cognition 2008 took place at Schloss Reinach near Freiburg (Germany) in September 2008. Besides the papers for oral presentation, more than 30 poster contributions were selected for presenting work in progress. The conference program also featured various tutorials, workshops, and a doctoral colloquium to promote an exchange of research experience of young scientists and knowledge transfer at an early stage of project development. Immediately before the conference, a workshop sponsored by the American National Science Foundation (NSF) was organized by the SILC consortium in cooperation with the SFB/TR 8 at the University of Freiburg. This workshop included lab visits at the Freiburg site of the SFB/TR 8. Many people contributed to the success of the Spatial Cognition 2008 conference. First of all, we thank the authors for preparing excellent contributions. This volume presents contributions by 61 authors on a large spectrum of interdisciplinary work on descriptions of space, on spatial mental models and maps, on spatio-temporal representation and reasoning, on route directions, wayfinding in natural and virtual environments, and spatial behavior, and on robot mapping and piloting. Our special thanks go to the members of the Program Committee for carefully reviewing and commenting on these contributions. Thorough reviews by peers are one of the most important sources of feedback to the authors

Preface

VII

that connects them to still-unknown territory and that helps them to improve their work and to secure a high-quality scientific publication. We thank Thomas F. Shipley for organizing, and Kenneth D. Forbus, Alexander Klippel, Marco Ragni, and Niels Krabisch for offering tutorials. For organizing workshops we owe thanks to Kenny Coventry and Jan M. Wiener as well as Alexander Klippel, Stephen Hirtle, Marco Ragni, Holger Schultheis, Thomas Barkowsky, Ronan O’Ceallaigh, and Wolfgang St¨ urzl. Further thanks go to Christoph H¨ olscher for organizing the poster session, and Sven Bertel and Marco Ragni, who were responsible for organizing the doctoral colloquium and for allocating travel grants to PhD students. We thank the members of our support staff, namely, Ingrid Schulz, Dagmar Sonntag, Roswitha Hilden, Susanne Bourjaillat, and Ulrich Jakob for professionally arranging many details. Special thanks go to Thomas Barkowsky, Eva R¨athe, Lutz Frommberger, and Matthias Westphal for the close cooperation on both sites of the SFB/TR 8. We thank Wolfgang Bay and the SICK AG for the generous sponsorship for this conference and the continuous support of scientific activities in and around Freiburg. We thank Daniel Schober and the ESRI Geoinformatik GmbH for sponsoring the travel grants to PhD students participating in the doctoral colloquium. We thank the Deutsche Forschungsgemeinschaft and the National Science Foundation and their program directors Bettina Zirpel, Gerit Sonntag, and SooSiang Lim for continued support of our research and for encouragement and enhancing our international research cooperations. For the review process and for the preparation of the conference proceedings we used the EasyChair conference management system, which we found convenient to use. Finally, we thank Alfred Hofmann and his staff at Springer for their continuing support of our book series as well as for sponsoring the Spatial Cognition 2008 Best Paper Award. September 2008

Christian Freksa Nora Newcombe Peter G¨ ardenfors Stefan W¨olfl

Conference Organization

Program Chairs Christian Freksa Nora S. Newcombe Peter G¨ ardenfors

Local Organization Stefan W¨olfl

Tutorial Chair

Poster Session Chair

Thomas F. Shipley

Christoph H¨ olscher

Workshop Chairs

Doctoral Colloquium Chairs

Kenny Coventry Jan M. Wiener

Sven Bertel Marco Ragni

Program Committee Pragya Agarwal Marios Avraamides Christian Balkenius Thomas Barkowsky John Bateman Brandon Bennett Michela Bertolotto Stefano Borgo Melissa Bowerman Angela Brunstein Wolfram Burgard Lily Chao Christophe Claramunt Eliseo Clementini Anthony Cohn Leila De Floriani

Maureen Donnelly Matt Duckham Russell Epstein Ron Ferguson Ken Forbus Antony Galton Susan Goldin-Meadow Gabriela Goldschmidt Klaus Gramann Christopher Habel Mary Hegarty Stephen Hirtle Christoph H¨ olscher Petra Jansen Gabriele Janzen Alexander Klippel

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Organization

Markus Knauff Stefan Kopp Maria Kozhevnikov Bernd Krieg-Br¨ uckner Antonio Kr¨ uger Benjamin Kuipers Yohei Kurata Gerhard Lakemeyer Longin Jan Latecki Hanspeter Mallot Mark May Timothy P. McNamara Tobias Meilinger Daniel R. Montello Stefan M¨ unzer Lynn Nadel Bernhard Nebel Marta Olivetti Belardinelli Dimitris Papadias Eric Pederson Ian Pratt-Hartmann

Additional Reviewers Daniel Beck Kirsten Bergmann Roberta Ferrario Alexander Ferrein Stefan Schiffer

Martin Raubal Terry Regier Kai-Florian Richter M. Andrea Rodr´ıguez Ute Schmid Amy Shelton Thomas F. Shipley Jeanne Sholl Barry Smith Kathleen Stewart Hornsby Holly Taylor Barbara Tversky Florian Twaroch David Uttal Constanze Vorwerg Stefan W¨olfl Thomas Wolbers Diedrich Wolter Nico Van de Weghe Wai Yeap

Related Book Publications

1. Winter, S., Duckham, M., Kulik, L., Kuipers, B. (eds.): COSIT 2007. LNCS, vol. 4736. Springer, Heidelberg (2007) 2. Fonseca, F., Rodr´ıguez, M.A., Levashkin, S. (eds.): GeoS 2007. LNCS, vol. 4853. Springer, Heidelberg (2007) 3. Barkowsky, T., Knauff, M., Ligozat, G., Montello, D.R. (eds.): Spatial Cognition 2007. LNCS (LNAI), vol. 4387. Springer, Heidelberg (2007) 4. Barker-Plummer, D., Cox, R., Swoboda, N. (eds.): Diagrams 2006. LNCS (LNAI), vol. 4045. Springer, Heidelberg (2006) 5. Raubal, M., Miller, H.J., Frank, A.U., Goodchild, M.F. (eds.): GIScience 2006. LNCS, vol. 4197. Springer, Heidelberg (2006) 6. Cohn, A.G., Mark, D.M. (eds.): COSIT 2005. LNCS, vol. 3693. Springer, Heidelberg (2005) 7. Rodr´ıguez, M.A., Cruz, I., Levashkin, S., Egenhofer, M.J. (eds.): GeoS 2005. LNCS, vol. 3799. Springer, Heidelberg (2005) 8. Meng, L., Zipf, A., Reichenbacher, T. (eds.): Map-based mobile services — Theories, methods and implementations. Springer, Berlin (2005) 9. Freksa, C., Knauff, M., Krieg-Br¨ uckner, B., Nebel, B., Barkowsky, T. (eds.): Spatial Cognition IV. LNCS (LNAI), vol. 3343. Springer, Heidelberg (2005) 10. Blackwell, A.F., Marriott, K., Shimojima, A. (eds.): Diagrams 2004. LNCS (LNAI), vol. 2980. Springer, Heidelberg (2004) 11. Egenhofer, M.J., Freksa, C., Miller, H.J. (eds.): GIScience 2004. LNCS, vol. 3234. Springer, Heidelberg (2004) 12. Gero, J.S., Tversky, B., Knight, T. (eds.): Visual and spatial reasoning in design III, Key Centre of Design Computing and Cognition. University of Sydney (2004) 13. Freksa, C., Brauer, W., Habel, C., Wender, K.F.: Spatial Cognition III. LNCS (LNAI), vol. 2685. Springer, Heidelberg (2003) 14. Kuhn, W., Worboys, M.F., Timpf, S. (eds.): COSIT 2003. LNCS, vol. 2825. Springer, Heidelberg (2003) 15. Hegarty, M., Meyer, B., Narayanan, N.H. (eds.): Diagrams 2002. LNCS (LNAI), vol. 2317. Springer, Heidelberg (2002) 16. Egenhofer, M.J., Mark, D.M. (eds.): GIScience 2002. LNCS, vol. 2478. Springer, Heidelberg (2002) 17. Barkowsky, T.: Mental Representation and Processing of Geographic Knowledge. LNCS (LNAI), vol. 2541. Springer, Heidelberg (2002) 18. Renz, J.: Qualitative Spatial Reasoning with Topological Information. LNCS (LNAI), vol. 2293. Springer, Heidelberg (2002) 19. Coventry, K., Olivier, P. (eds.): Spatial language: Cognitive and computational perspectives. Kluwer, Dordrecht (2002) 20. Montello, D.R. (ed.): COSIT 2001. LNCS, vol. 2205. Springer, Heidelberg (2001) 21. Gero, J.S., Tversky, B., Purcell, T. (eds.): Visual and spatial reasoning in design II. Key Centre of Design Computing and Cognition. University of Sydney (2001) 22. Habel, C., Brauer, W., Freksa, C., Wender, K.F. (eds.): Spatial Cognition 2000. LNCS (LNAI), vol. 1849. Springer, Heidelberg (2000) 23. Habel, C., von Stutterheim, C. (eds.): R¨ aumliche Konzepte und sprachliche Strukturen. Niemeyer, T¨ ubingen (2000)

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24. Freksa, C., Mark, D.M. (eds.): COSIT 1999. LNCS, vol. 1661. Springer, Heidelberg (1999) 25. Gero, J.S., Tversky, B. (eds.): Visual and spatial reasoning in design. Key Centre of Design Computing and Cognition. University of Sydney (1999) 26. Habel, C., Werner, S. (eds.): Special issue on spatial reference systems, Spatial Cognition and Computation, vol. 1(4) (1999) 27. Freksa, C., Habel, C., Wender, K.F. (eds.): Spatial Cognition 1998. LNCS (LNAI), vol. 1404. Springer, Heidelberg (1998) 28. Hirtle, S.C., Frank, A.U. (eds.): COSIT 1997. LNCS, vol. 1329. Springer, Heidelberg (1997) 29. Kuhn, W., Frank, A.U. (eds.): COSIT 1995. LNCS, vol. 988. Springer, Heidelberg (1995)

Table of Contents

Invited Talks Virtual Reality as a Valuable Research Tool for Investigating Different Aspects of Spatial Cognition (Abstract) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heinrich H. B¨ ulthoff, Jennifer L. Campos, and Tobias Meilinger

1

On the “Whats” and “Hows” of “Where”: The Role of Salience in Spatial Descriptions (Abstract) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laura A. Carlson

4

Learning about Space (Abstract) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dedre Gentner

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Spatial Orientation Does Body Orientation Matter When Reasoning about Depicted or Described Scenes? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marios N. Avraamides and Stephanie Pantelidou Spatial Memory and Spatial Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jonathan W. Kelly and Timothy P. McNamara

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22

Spatial Navigation Map-Based Spatial Navigation: A Cortical Column Model for Action Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Louis-Emmanuel Martinet, Jean-Baptiste Passot, Benjamin Fouque, Jean-Arcady Meyer, and Angelo Arleo Efficient Wayfinding in Hierarchically Regionalized Spatial Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thomas Reineking, Christian Kohlhagen, and Christoph Zetzsche Analyzing Interactions between Navigation Strategies Using a Computational Model of Action Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . Laurent Doll´e, Mehdi Khamassi, Benoˆıt Girard, Agn`es Guillot, and Ricardo Chavarriaga A Minimalistic Model of Visually Guided Obstacle Avoidance and Path Selection Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lorenz Gerstmayr, Hanspeter A. Mallot, and Jan M. Wiener

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56

71

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Spatial Learning Route Learning Strategies in a Virtual Cluttered Environment . . . . . . . . . Rebecca Hurlebaus, Kai Basten, Hanspeter A. Mallot, and Jan M. Wiener Learning with Virtual Verbal Displays: Effects of Interface Fidelity on Cognitive Map Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nicholas A. Giudice and Jerome D. Tietz Cognitive Surveying: A Framework for Mobile Data Collection, Analysis, and Visualization of Spatial Knowledge and Navigation Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drew Dara-Abrams

104

121

138

Maps and Modalities What Do Focus Maps Focus On? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kai-Florian Richter, Denise Peters, Gregory Kuhnm¨ unch, and Falko Schmid Locating Oneself on a Map in Relation to Person Qualities and Map Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lynn S. Liben, Lauren J. Myers, and Kim A. Kastens Conflicting Cues from Vision and Touch Can Impair Spatial Task Performance: Speculations on the Role of Spatial Ability in Reconciling Frames of Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Madeleine Keehner

154

171

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Spatial Communication Epistemic Actions in Science Education . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kim A. Kastens, Lynn S. Liben, and Shruti Agrawal An Influence Model for Reference Object Selection in Spatially Locative Phrases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michael Barclay and Antony Galton

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216

Spatial Language Tiered Models of Spatial Language Interpretation . . . . . . . . . . . . . . . . . . . . Robert J. Ross

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Perspective Use and Perspective Shift in Spatial Dialogue . . . . . . . . . . . . . Juliana Goschler, Elena Andonova, and Robert J. Ross

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Table of Contents

Natural Language Meets Spatial Calculi . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joana Hois and Oliver Kutz Automatic Classification of Containment and Support Spatial Relations in English and Dutch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kate Lockwood, Andrew Lovett, and Ken Forbus

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283

Similarity and Abstraction Integral vs. Separable Attributes in Spatial Similarity Assessments . . . . . Konstantinos A. Nedas and Max J. Egenhofer Spatial Abstraction: Aspectualization, Coarsening, and Conceptual Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lutz Frommberger and Diedrich Wolter

295

311

Concepts and Reference Frames Representing Concepts in Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Martin Raubal The Network of Reference Frames Theory: A Synthesis of Graphs and Cognitive Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tobias Meilinger

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Spatially Constrained Grammars for Mobile Intention Recognition . . . . . Peter Kiefer

361

Modeling Cross-Cultural Performance on the Visual Oddity Task . . . . . . Andrew Lovett, Kate Lockwood, and Kenneth Forbus

378

Spatial Modeling and Spatial Reasoning Modelling Scenes Using the Activity within Them . . . . . . . . . . . . . . . . . . . . Hannah M. Dee, Roberto Fraile, David C. Hogg, and Anthony G. Cohn Pareto-Optimality of Cognitively Preferred Polygonal Hulls for Dot Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Antony Galton

394

409

Qualitative Reasoning about Convex Relations . . . . . . . . . . . . . . . . . . . . . . Dominik L¨ ucke, Till Mossakowski, and Diedrich Wolter

426

Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

441

Virtual Reality as a Valuable Research Tool for Investigating Different Aspects of Spatial Cognition (Abstract) Heinrich H. B¨ ulthoff, Jennifer L. Campos, and Tobias Meilinger Max-Planck-Institute for Biological Cybernetics Spemannstr. 38, 72076 T¨ ubingen, Germany {heinrich.buelthoff,jenny.campos,tobias.meilinger}@tuebingen.mpg.de

The interdisciplinary research field of spatial cognition has benefited greatly from the use of advanced Virtual Reality (VR) technologies. Such tools have provided the ability to explicitly control specific experimental conditions, manipulate variables not possible in the real world, and provide a convincing, multimodal experience. Here we will first describe several of the VR facilities at the Max Planck Institute (MPI) for Biological Cybernetics that have been developed to optimize scientific investigations related to multi-modal self-motion perception and spatial cognition. Subsequently, we will present some recent empirical work contributing to these research areas. While in the past, low-quality visual simulations of space were the most prominent types of VR (i.e., simple desktop displays), more advanced visualization systems are becoming increasingly more desirable. At the MPI we have utilized a variety of visualization tools ranging from immersive head-mounted displays (HMD), to large field-of-view, curved projection systems, to a high resolution tiled display. There is also an increasing need for high-quality, adaptable, largescale, simulated environments. At the MPI we have created a virtual replica of downtown T¨ ubingen throughout which observers can navigate. In collaboration with ETH Zurich, who have developed “CityEngine”, a virtual city builder, we are now able to rapidly create virtual renditions of existing cities or customized environmental layouts. In order to naturally interact within such virtual environments (VEs), it is also increasingly more important to be able to physically move within these spaces. Under most natural conditions involving self-motion, bodybased information is inherently present. Therefore, the recent developments of several sophisticated self-motion interfaces have allowed us to present and evaluate natural, multi-sensory navigational experiences in unprecedented ways. For instance, within a large (12 m×12 m), free-walking space, a high-precision optical tracking system (paired with an HMD) updates one’s position within a VE as they naturally navigate through walking or when passively transported (i.e., via a robotic wheelchair). Further, the MPI Motion Simulator is a 6-degree of freedom anthropomorphic robotic arm that can translate and rotate an observer C. Freksa et al. (Eds.): Spatial Cognition VI, LNAI 5248, pp. 1–3, 2008. c Springer-Verlag Berlin Heidelberg 2008 

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H.H. B¨ ulthoff, J.L. Campos, and T. Meilinger

in any number of ways (both open and closed-loop). Finally, a new, state-of-theart omni-directional treadmill now offers observers the opportunity to experience unrestricted, limitless walking throughout large-scale VE’s. When moving through space, both, dynamic visual information (i.e., optic flow), and body-based information (i.e., proprioceptive/efference copy and vestibular) jointly specify the magnitude of a distance travelled. Relatively little is currently known about how these cues are integrated when simultaneously present. In a series of experiments, we investigated participants’ ability to estimate travelled distances under a variety of sensory/motor conditions. Visual information presented via an HMD was combined with body-based cues that were provided either by walking in a fully-tracked, free-walking space, by walking on a large linear treadmill, or by being passively transported in a robotic wheelchair. Visually-specified distances were either congruent or incongruent with distances specified by body-based cues. Responses reflect a combined effect of both visual and body-based information, with an overall higher weighting of body-based cues during walking and a relatively equal weighting of inertial and visual cues during passive movement. The characteristics of self-motion perception have also been investigated using a novel continuous pointing method. This task simply requires participants to view a target and point continuously towards the target as they moved past it along a straight, forward trajectory. By using arm angle, we are able to measure perceived location and, hence, perceived self-velocity during the entire trajectory. We have compared the natural characteristics of continuous pointing during sighted walking with those during reduced sensory/motor cue conditions, including: blind-walking, passive transport, and imagined walking. The specific characteristics of self-motion perception during passive transport have also been further evaluated through the use of a robotic wheelchair and the MPI Motion Simulator. Additional research programs have focused on understanding particular aspects of spatial memory when navigating through visually rich, complex environments. In one study that investigated route memory, participants navigated through virtual T¨ ubingen while it was projected onto a 220◦ field-of-view, curved screen display. Participants learned two routes while they were simultaneously required to perform a visual, spatial, or verbal secondary task. In the subsequent wayfinding phase the participants were asked to locate and “virtually travel” along the two routes again (via joystick manipulation). During this wayfinding phase a number of dependent measures were recorded. The results indicate that encoding wayfinding knowledge interfered with the verbal and spatial secondary tasks. These interferences were even stronger than the interference of wayfinding knowledge with the visual secondary task. These findings are consistent with a dual-coding approach of wayfinding knowledge. This dual coding approach was further examined in our fully-tracked, free-walking space. In this case, participants walked a route through a virtual environment and again were required to remember the route. For 50% of the intersections they encountered, they were asked associate it with an arbitrary name they heard via headphones (e.g., “Goethe place”). For the other 50% of the intersections they were asked to remember the intersection by the local environmental features and not associate

Virtual Reality as a Valuable Research Tool

3

it with a name. In a successive route memory test participants were “beamed” to an intersection and had to indicate in which direction they originally traveled the route. Participants performed better at intersections without a name than they did for intersections associated with an arbitrary name. When repeating the experiment with meaningful names that accurately represented the environmental features (e.g., “Hay place”), the results turned around (i.e., naming a place no longer lead to worse performance). These results indicate that the benefits of language do not come for free.

References 1. Berger, D.R., Terzibas, C., Beykirch, K., B¨ ulthoff, H.H.: The role of visual cues and whole-body rotations in helicopter hovering control. In: Proceedings of the AIAA Modeling and Simulation Technologies Conference and Exhibit (AIAA 2007), Reston, VA, USA. American Institute of Aeronautics and Astronautics (2007) 2. B¨ ulthoff, H.H., van Veen, H.A.H.C.: Vision and action in virtual environments: Modern psychophysics in spatial cognition research. In: Jenkin, M., Harris, M.L. (eds.) Vision and Attention, pp. 233–252. Springer, Heidelberg (2000) 3. Campos, J.L., Butler, J.S., Mohler, B.J., B¨ ulthoff, H.H.: The contributions of visual flow and locomotor cues to walked distance estimation in a virtual environment. In: Proceedings of the 4th Symposium on Applied Perception in Graphics and Visualization, p. 146. ACM Press, New York (2007) 4. Meilinger, T., Knauff, M., B¨ ulthoff, H.H.: Working memory in wayfinding - a dual task experiment in a virtual city. Cognitive Science 32, 755–770 (2008) 5. Mohler, B.J., Campos, J.L., Weyel, M., B¨ ulthoff, H.H.: Gait parameters while walking in a head-mounted display virtual environment and the real world. In: Proceedings of Eurographics 2007, Eurographics Association, pp. 85–88 (2007) 6. Teufel, H.J., Nusseck, H.-G., Beykirch, K.A., Butler, J.S., Kerger, M., B¨ ulthoff, H.H.: MPI motion simulator: Development and analysis of a novel motion simulator. In: Proceedings of the AIAA Modeling and Simulation Technologies Conference and Exhibit (AIAA 2007), Reston, VA, USA. American Institute of Aeronautics and Astronautics (2007)

On the “Whats” and “Hows” of “Where”: The Role of Salience in Spatial Descriptions (Abstract) Laura A. Carlson Department of Psychology, University of Notre Dame, USA

According to Clark [1] language is a joint activity between speaker and listener, undertaken to accomplish a shared goal. In the case of spatial descriptions, one such goal is for a speaker to assist a listener in finding a sought-for object. For example, imagine misplacing your keys on a cluttered desktop, and asking your friend if s/he knows where they are. In response, there are a variety of spatial descriptions that your friend can select that vary in complexity, ranging from a simple deictic expression such as “there” (and typically accompanied by a pointing gesture), to a much more complicated description such as “its on the desk, under the shelf, to the left of the book and in front of the phone.” Between these two extremes are descriptions of the form “The keys are by the book”, consisting of three parts: the located object that is being sought (i.e., the keys); the reference object from which the location of the located object is specified (i.e., the book) and the spatial term that conveys the spatial relation between these two objects (i.e., by). For inquiries of this type (“where are my keys?”), the located object is pre-specified, but the speaker needs to select an appropriate spatial term and an appropriate reference object. My research focuses on the representations and processes by which a speaker selects these spatial terms and reference objects, and the representations and processes by which a listener comprehends these ensuing descriptions. The “Whats” With respect to selection, one important issue is understanding why particular terms and particular reference objects are chosen. For a given real-world scene, there are many possible objects that stand in many possible relations with respect to a given located object. On what basis might a speaker make his/her selection? Several researchers argue that reference objects are selected on the basis of properties that make them salient relative to other objects [2,3,4]. Given the purpose of the description as specifying the location of the sought-for object, it would make sense that the reference object be easy to find among the other objects in the display. However, there are many different properties that could define salience, including spatial features, perceptual properties, and conceptual properties. With respect to spatial features, certain spatial relations are preferred over others. For example, objects that stand in front/back relations to a given located object are preferred to objects that stand in left/right relations [5]. This is consistent C. Freksa et al. (Eds.): Spatial Cognition VI, LNAI 5248, pp. 4–6, 2008. c Springer-Verlag Berlin Heidelberg 2008 

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with well-known differences in the ease of processing different terms [6,7]. In addition, distance may play an important role, with objects that are closer to the located object preferred to those that are more distant [8]. Thus, all else being equal, a reference object may be selected because it is closest to the located object and/or stands in a preferred relation with respect to the located object. With respect to perceptual features, Talmy [4] identified size and movability as key dimensions, with larger and immovable objects preferred as reference objects. In addition, there may be a preference to select more geometrically complex objects as reference objects. Blocher and Stopp [9] argued for color, shape and size as critical salient dimensions. Finally, de Vega et al. [2] observed preferences for reference objects that are inanimate, more solid, and whole rather than parts of objects. Finally, with respect to conceptual features, reference objects are considered “given” objects, less recently mentioned into the discourse [4]. In addition, there may be a bias to select reference objects that are functionally related to the located object [10,11]. In this talk I will present research from my lab in which we systematically manipulate spatial, conceptual and perceptual features, and ask which dimensions are influential in reference object selection, and how priorities are assigned across the spatial, perceptual and conceptual dimensions. Both production and comprehension measures will be discussed. This work will provide a better sense of how salience is being defined with respect to selecting a reference object for a spatial description. The “Hows” Implicit in the argument that the salience of an object is computed across these dimensions is the idea that such computation requires that multiple objects are evaluated and compared among each other along these dimensions. That is, to say an object stands out relative to other objects (for example, a red object among black objects) requires that the color of all objects (black and red) be computed and compared, and that on the basis of this comparison, the unique object (in this case, red) stands out (among black). Put another way, an object can only stand out relative to a contrast set [12]. Research in my lab has examined how properties of various objects are evaluated and compared during production and comprehension, and in particular, the point in processing at which properties of multiple objects exert their influence. For example, we have shown that the presence, placement and properties of surrounding objects have a significant impact during comprehension and production [13,11]. I will discuss these findings in detail, and will present electrophysiological data that illustrate within the time course of processing the point at which these features have an impact. The Main Points The main points of the talk will be an identification of the features and dimensions that are relevant for selecting a reference object, and an examination of how

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and when these features and dimensions have an impact on processing spatial descriptions. Implications for other tasks and other types of spatial descriptions will be discussed.

References 1. Clark, H.H.: Using language. Cambridge University Press, Cambridge (1996) 2. de Vega, M., Rodrigo, M.J., Ato, M., Dehn, D.M., Barquero, B.: How nouns and prepositions fit together: An exploration of the semantics of locative sentences. Discourse Processes 34, 117–143 (2002) 3. Miller, G.A., Johnson-Laird, P.N.: Language and perception. Harvard University Press, Cambridge (1976) 4. Talmy, L.: How language structures space. In: Pick, H.L., Acredolo, L.P. (eds.) Spatial orientation: Theory, research, and application, pp. 225–282. Plenum, New York (1983) 5. Craton, L.G., Elicker, J., Plumert, J.M., Pick Jr., H.L.: Children’s use of frames of reference in communication of spatial location. Child Developmen 61, 1528–1543 (1990) 6. Clark, H.H.: Space, time, semantics, and the child. In: Moore, T.E. (ed.) Cognitive development and the acquisition of language. Academic Press, New York (1973) 7. Fillmore, C.J.: Santa Cruz lectures on deixis. Indiana University Linguistics Club, Bloomington (1971) 8. Hund, A.M., Plumert, J.M.: What counts as by? Young children’s use of relative distance to judge nearbyness. Developmental Psychology 43, 121–133 (2007) 9. Blocher, A., Stopp, E.: Time-dependent generation of minimal sets of spatial descriptions. In: Olivier, P., Gapp, K.P. (eds.) Representation and processing of spatial relations, pp. 57–72. Erlbaum, Mahwah (1998) 10. Carlson-Radvansky, L.A., Tang, Z.: Functional influences on orienting a reference frame. Memory & Cognition 28, 812–820 (2000) 11. Carlson, L.A., Hill, P.L.: Processing the presence, placeent and properties of a distractor in spatial language tasks. Memory & Cognition 36, 240–255 (2008) 12. Olson, D.: Language and thought: Aspects of a cognitive theory of semantics. Psychological Review 77, 143–184 (1970) 13. Carlson, L.A., Logan, G.D.: Using spatial terms to select an object. Memory & Cognition 29, 883–892 (2001)

Learning about Space (Abstract) Dedre Gentner Department of Psychology, Northwestern University, USA

Spatial cognition is important in human learning, both in itself and as a major substrate of learning in other domains. Although some aspects of spatial cognition may be innate, it is clear that many important spatial concepts must be learned from experience. For example, Dutch and German use three spatial prepositions—op, aan, and om in Dutch—to describe containment and support relations, whereas English requires just one preposition—on—to span this range. How do children learn these different ways of partitioning the world of spatial relations? More generally, how do people come to understand powerful spatial abstractions like parallel, convergent, proportionate, and continuous? I suggest that two powerful contributors to spatial learning are analogical mapping— structural alignment and abstraction—and language, especially relational language, which both invites and consolidates the insights that arise from analogical processes. I will present evidence that (1) analogical processes are instrumental in learning new spatial relational concepts; and, further, that (2) spatial relational language fosters analogical processing. I suggest that mutual bootstrapping between structure-mapping processes and relational language is a major contributor to spatial learning in humans.

C. Freksa et al. (Eds.): Spatial Cognition VI, LNAI 5248, p. 7, 2008. c Springer-Verlag Berlin Heidelberg 2008 

Does Body Orientation Matter When Reasoning about Depicted or Described Scenes?* Marios N. Avraamides and Stephanie Pantelidou Department of Psychology, University of Cyprus P.O. Box 20537, 1678 Nicosia, Cyprus [email protected], [email protected]

Abstract. Two experiments were conducted to assess whether the orientation of the body at the time of test affects the efficiency with which people reason about spatial relations that are encoded in memory through symbolic media. Experiment 1 used depicted spatial layouts while Experiment 2 used described environments. In contrast to previous studies with directly-experienced spatial layouts, the present experiments revealed no sensorimotor influences on performance. Differences in reasoning about immediate and non-immediate environments are thus discussed. Furthermore, the same patterns of findings (i.e., normal alignment effects) were observed in the two experiments supporting the idea of functional equivalence of spatial representations derived from different modalities. Keywords: body orientation, sensorimotor interference, perspective-taking, spatial reasoning.

1 Introduction While moving around in the environment people are able to keep track of how egocentric spatial relations (i.e., self-to-object directions and distances) change as a result of their movement [1-4]. To try out an example, choose one object from your immediate surroundings (e.g., a chair), and point to it. Then, close your eyes and take a few steps forward and/or rotate yourself by some angle. As soon as you finish moving, but before opening your eyes, point to the object again. It is very likely that you pointed very accurately and without taking any time to contemplate where the object might be as a result of your movement. This task which humans can carry out with such remarkable efficiency and speed entails rather complex mathematical computations. It requires that the egocentric location of an object is initially encoded and then continuously updated while moving in the environment. The mechanism that allows people to update egocentric relations and stay oriented within their immediate surroundings is commonly known as spatial updating. Several studies have suggested that spatial updating takes place automatically with physical movement because such movement provides the input that is necessary for *

The presented experiments have been conducted as a part of an undergraduate thesis by Stephanie Pantelidou.

C. Freksa et al. (Eds.): Spatial Cognition VI, LNAI 5248, pp. 8–21, 2008. © Springer-Verlag Berlin Heidelberg 2008

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updating [2, 4]. In the case of non-visual locomotion this input consists of kinesthetic cues, vestibular feedback, and copies of efferent commands. The importance of physical movement is corroborated by empirical findings showing that participants point to a location equally fast and accurately from an initial standpoint and a novel standpoint they adopt by means of physical movement (as in the example above). In contrast, when the novel standpoint is adopted by merely imagining the movement, participants are faster and more accurate to respond from their initial than their novel (imagined) standpoint [5]. This is particularly the case when an imagined rotation is needed to adopt the novel standpoint. The traditional account for spatial updating [4, 6] posits that spatial relations are encoded and updated on the basis of an egocentric reference frame (i.e., a reference frame that is centered on one´s body). Because egocentric relations are continuously updated when moving, reasoning from one’s physical perspective is privileged as it can be carried out on the basis of relations that are directly represented in memory. Instead, reasoning from imagined perspectives is deliberate and effortful as it entails performing “off-line” mental transformations to compute the correct response. Recently, May proposed the sensorimotor interference account which places the exact locus of difficulty for responding from imagined perspectives at the presence of conflicts between automatically-activated sensorimotor codes that specify locations relative to the physical perspective and cognitive codes that define locations relative to the imagined perspective [7, 8]. Based on this account, while responding from an actual physical perspective is facilitated by compatible sensorimotor codes, in order to respond from an imagined perspective, the incompatible sensorimotor codes must be inhibited while an alternative response is computed. The presence of conflicts reduces accuracy and increases reaction time when reasoning from imagined perspectives. In a series of elegant experiments, May provided support for the facilitatory and interfering effects of sensorimotor codes [7]. Recently, Kelly, Avraamides, and Loomis [9] dissociated the influence of sensorimotor interference in spatial reasoning from effects caused by the organizational structure of spatial memory (see also [10]). In one condition of the study participants initially examined a spatial layout of 9 objects from a fixed standpoint and perspective. Then, they were asked to rotate 90° to their left or right to adopt a novel perspective. From this perspective participants carried out a series of localization trials that involved pointing to object locations from various imagined perspectives. This paradigm allowed dissociating the orientation of the testing perspective from that of the perspective adopted during learning. This dissociation is deemed necessary in light of evidence from several studies showing that spatial memories are stored with a preferred direction that is very often determined by the learning perspective [11]. Results revealed that responding from imagined perspectives that coincided with either the learning or the testing perspective was more efficient compared to responding from other perspectives. A similar result was obtained in the earlier study of Mou, McNamara, Valiquette, and Rump [10] which suggested that independent effects attributed to the orientation of the body of the observer at test and the preferred storage orientation of spatial memory can be obtained in spatial cognition experiments. Kelly et al, have termed the former effect as the sensorimotor alignment effect and the latter as the memory-encoding alignment effect.

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In order to investigate the boundary conditions of sensorimotor facilitation/interference, Kelly et al included an experimental condition in which participants performed testing trials after having moved to an adjacent room. Results from this condition revealed that when participants reasoned about relations that were not immediately present, no sensorimotor interference/facilitation was exerted on performance. Only a memory-encoding alignment effect was obtained in this condition. The study by Kelly et al. provided evidence that the orientation of one´s body when reasoning about space influences performance only when immediate spatial relations are retrieved. Presumably this occurs because egocentric relations are maintained in a transient sensorimotor representation that functions to encode and automatically update egocentric directions and distances to objects in one´s immediate surroundings [12, 13]. When reasoning about remote environments such a representation is of little, if any, use. In this case, a more enduring, perhaps allocentric, representation would more suitably provide the information needed to compute the spatial relations as needed (see [14] for a comprehensive review of theories of memory that provide for multiple encoding systems). If this is true, then the same pattern of findings (i.e., presence of memory-encoding alignment effect but no sensorimotor alignment effect) should be expected when people reason about spatial relations included in any remote environment regardless of how it is encoded. Although we very frequently in our daily lives reason about environments that we have previously experienced directly, in many cases we process spatial relations that have been committed to memory through symbolic media such as pictures, movies, language etc (e.g., planning a route after having studied a map). While numerous studies have been carried out to examine how people reason about depicted or described experiments, most studies have either focused on examining effects caused by the misalignment between medium and actual space [15] or have confounded the orientations of the learning and testing perspectives [16] . As a result, it is not yet known whether the orientation of the observer’s body mediates spatial reasoning for environments encoded through symbolic media. The goal of the present study is to assess whether the orientation of the body influences performance when reasoning about spatial relations contained in depicted (Experiment 1) or a described (Experiment 2) remote layout. We expect that the use of remote environments will give rise to a pattern of findings similar to those obtained in conditions in which participants are tested after being removed from the learning environment. If such a result is obtained, it would further highlight the fundamental difference between “online” reasoning about immediate environments and “off-line” reasoning about remote environments. A secondary goal of the study is to compare spatial reasoning for depicted and linguistic spatial scenes in order to assess the functional equivalence of spatial layouts that are derived from different modalities. This is a question that has accumulated increased theoretical interest in recent years, presumably because it bears important implications for modern tools and applications that rely on sensory substitution, as in the case of navigational systems for the blind. Most previous studies tested functional equivalence using environments that were immediate to participants [1719]. Although some indirect evidence suggests that learning an environment from a map or text engages the same parieto-frontal network in the brain [20, 21], it is important to test whether the same behavioral effects are found when reasoning for spatial relations derived from different modalities. By comparing the findings of Experiments

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1 and 2 in the present study, we will be able to assess the degree of functional equivalence between scenes that are learned though pictures and language. Based on evidence from previous studies that examined the organization of spatial memories derived from maps and linguistic descriptions [22, 23], we expect that similar patterns of findings will be found in the two experiments. For the present experiments we adopted the paradigm used by Waller, Montello, Richardson, and Hegarty [24] and previously by Presson and Hazelrigg [15]. In these studies participants first learned various 4-point paths and then made judgments of relative direction by adopting imagined perspectives within the paths. Trials could be classified as aligned (i.e., the orientation of the imagined perspective matched the physical perspective of the participant) or as contra-aligned (i.e., the imagined perspective deviated 180° from the physical perspective of the participant). The typical result when participants carry out the task without moving from the learning standpoint/perspective (Stay condition in [24]) is that performance is more efficient in aligned than contra-aligned trials. This finding is commonly referred to as an alignment effect. Additional interesting conditions were included in the study by Waller. In experiment 2, a Rotate condition was included. In this condition, participants performed the task after having physically rotated 180°. The rationale was that if the alignment effect is caused primarily by the learning orientation then a similar alignment effect to that of the Stay condition would be obtained. However, if the alignment effect is caused by the influence of the orientation of the body at the time of test, a reverse-alignment effect should be expected. Results, however, revealed no alignment effect (see also[25]). Two additional conditions, namely the Rotate-Update and the Rotate-Ignore, provided important results. In the Rotate-Update condition participants were instructed to physically rotate 180° in place and imagine that the spatial layout was behind them (i.e., they updated their position relative to the learned layout). In the Rotate-Ignore condition participants also rotated by 180° but were asked to imagine that the learned layout had rotated along with them. Results revealed a normal alignment effect in the rotate-ignore condition but a reverse-alignment effect in the rotate-update condition. Overall, these findings suggest that the orientation of the body is important when reasoning about immediate environments. In the present experiments we adopted the rationale of Waller et al. to examine the presence of normal vs. reverse alignment effects in Stay and Rotate conditions. However, in contrast to Waller et al., the paths that we have used were not directly experienced by participants. Instead, they were presented on a computer monitor as either pictures (Experiment 1) or text route descriptions (Experiment 2). If the orientation of the body of the participant at the time of test influences performance, a normal alignment effect should be found in Stay conditions and a reverse alignment effect should be obtained in Rotate conditions. However, if the learning perspective dominates performance then a normal alignment effect should be expected in both Stay and Rotate conditions. Finally, a third possibility is that both the learning and physical perspectives influence performance, as shown by Kelly et al for immediate environments. In that case, if the two effects are of equal magnitude then no alignment effect should be expected in Rotate conditions as the two effects would cancel each other out. However, without making any assumptions about the magnitude of the two effects, we should at least expect a reduced alignment effect in Rotate conditions, if indeed both learning and physical perspectives influence reasoning.

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2 Experiment 1 In Experiment 1 participants encoded paths that were depicted on a computer screen and then carried out judgments of relative direction (JRD’s). A Stay condition and a Rotate condition (in which neither update nor ignore instructions were given) were included. Based on previous findings documenting that the orientation of one’s body does not typically influence spatial reasoning about non-immediate environments, we predict that a normal alignment effect would be present in both the Stay and Rotate conditions. We also expect that overall performance will be equal in the Stay and Rotate conditions. 2.1 Method Participants Twenty-two students from an introductory psychology course at the University of Cyprus participated in the experiment in exchange for course credit. Twelve were assigned to the Stay condition and 10 to the Rotate condition. Design A 2 (observer position: Stay vs Rotate) x 3 (imagined perspective: aligned 0°, misaligned 90°, contra-aligned 180°) mixed factorial design was used. Observer position was manipulated between subjects while imagined perspective varied within-subjects. Materials and Apparatus Two 19” LCD monitors attached to a computer running the Vizard software (from WorldViz, Santa Barbara, CA) were used to display stimuli. The monitors were placed facing each other and participants sat on a swivel chair placed in-between the two monitors. Four paths were created as models with Source SDK (from Valve Corporation). Oblique screenshots of these models constituted the spatial layouts that participants learned. Each path comprised of 4 segments of equal length that connected 5 numbered location points (Figure 1). Pointing responses were made using a joystick with the angle of deflection and latency of pointing being recorded by the computer at each trial. 2.2 Procedure Prior to the beginning of the experiment participants were shown example paths on paper and were instructed on how to perform JRD’s. JRD’s involve responding to statements of the form “imagine being at x, facing y. Point to z” were x, y, and z are objects/landmarks from the studied layout. Prior to the beginning of the experiment participants were asked to perform various practice trials with JRD’s using campus landmarks as targets and responding both with their arms and the joystick. Then, participants were seated in front of one of the monitors and were asked to study the first path. They were instructed to visualize themselves moving on the path. The

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Fig. 1. Example of a path used in Experiment 1

initial direction of imagined movement was to the left for two paths and to the right in the other two (e.g., Figure 1). This was done to avoid confounding the initial movement direction with either the orientation of the body or the one opposite to it. Participants were given unlimited time to memorize the path and then proceeded to perform the experimental trials. Each trial instructed them to imagine adopting a perspective within the memorized path (e.g., Imagine standing at 1 facing 2) and point from it with the joystick toward a different position in the path (e.g., Point to 3). Participants in the Stay condition performed the trials on the same monitor on which they have previously viewed the path. Those in the Rotate condition were asked to rotate 180° and perform the pointing trials on the other monitor. Participants were instructed to respond as fast as possible but without sacrificing accuracy. Sixteen trials for each path were included yielding to a total of 64 trials per subject. Four imagined perspectives (i.e., aligned 0°, misaligned 90° left, misaligned 90° right, and contra-aligned 180°) were equally represented in the 64 trials. Furthermore, correct pointing responses, which could be 45°, 90°, and 135° to the left and right of the forward joystick position, were equally distributed across the four imagined perspectives. The order of trials within each path was randomized. Also, the order in which the four paths were presented to participants varied randomly.

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2.3 Results Separate analyses for pointing accuracy and latency for correct responses were carried out. In order to classify responses as correct and incorrect, joystick deflection angles were quantized as follows. Responses between 22.5° and 67.5° from to forward position of the joystick were classified as 45° responses to the left or right depending on the side of deflections. Similarly, responses that fell between 67.5° and 112.5° were considered as 90° responses to the left or right. Finally, responses between 112.5° and 157.5° were marked as 135° responses. Initial analyses of accuracy and latency involving all four imagined perspectives revealed no differences between the 90° left and the 90° right perspectives in either Stay or rotate conditions. Therefore, data for these two perspectives were averaged to form a misaligned 90° condition. A 2 (observer position) x 3 (imagined perspective) mixed-model Analysis of Variance (ANOVA) was conducted for both accuracy and latency data. Accuracy The analysis revealed that overall accuracy was somewhat higher in the Stay (79,9%) than in the Rotate (73,9%) condition. However, this difference did not reach statistical significance, F(1,20)=.92, p=.35, η2 =.04. A significant main effect for imagined perspective was obtained, F(2,40)=8.44, p