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Sensorimotor Processing of Vertical Disparity

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Sensorimotor Processing of Vertical Disparity SENSORIMOTOR PROCESSING OF VERTICAL DISPARITY ROBERT SCOTT ALLISON A thesis submitted to the Faculty of Graduate Studies in partial fulfilment of the requirements for the degree of Doctor of Philosophy Graduate Programme in Biology York University Toronto, Ontario March 1998 Natioral Library Bibliothèque nationale 191 of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395, rue Wellington OttawaON K1AON4 Ottawa ON K1A ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seIl reproduire, prêter, distribuer ou copies of ths thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/^, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otheIUrise de celle-ci ne doivent être imprimés reproduced without the author' s ou autrement reproduits sans son permission. autorisation. SENSORIMOTOR PROCESSING OF VERTICAL DZSPARITY by Robert S. Allison a dissertation subrnitted to the Faculty of Graduate Studies of York University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Permission has been granted to the LIBRARY OF YORK UNIVERSITY to lend or sel1 copies of this dissertation. to the NATIONAL LIBRARY OF CANADA to microfilm this dissertation and to tend or seil copies of the film, and to UNIVERSITY MICROFILMS to publish an abstract of this dissertation. The author reserves other publication rights. and neither the dissertation nor extensive extracts from it may be printed or otherwise reproduced without the author's written permission. Several recent computational theories of binocular vision have proposed that vertical disparities play a critical role in calibrating and scaling stereoscopic depth. In these theories. vertical disparities specify "viewing system" pararneters such as the viewing distance and the relative alignment and magnification of the images in the two eyes. 1hypothesised that vertical disparities are temporally integrated and therefore processed more slowly than horizontal disparities. This averaging would allow robust estimation of slowly changing pararneters. The temporal characteristics of vertical and horizontal disparity processing in human vision were investigated in three sets of experiments. First. scleral search coils were used to measure the gain and phase of vertical vergence as a function of stimulus disparity and temporal frequency. The half images in a large. textured. stereoscopic display were oscillated in counter-phase to evoke vertical vergence. At low frequencies and amplitudes. the gain of vertical vergence was near one and phase lag was srnall. Gain declined and phase lag increased with increasing stimulus frequency. The dynamics of vertical vergence tailor it ro compensate for disturbances in vertical eye alignment. Second, the temporal characteristics of the slant or inclination percepts evoked by linear transformations of disparity (shear or scale dispari ties) were studied. Stimuli contained combinations of horizontal and vertical size or shear disparities that were introduced stepwise or modulated sinusoidally. Subjects matched perceived slant or inclination with that of a visual cornparison surface. There were no clear differences in the effects of exposure time or temporal frequency on slant or inclination percepts induced by horizontal disparity and those induced by vertical disparity. Considerable individual differences were found and several subjects experienced slant reversal. particularly with oscillating stimuli. Perceived slant induced by oscillations of dilation disparity was in the direction of the vertical component. Percepts of slant and inclination also depend on monocular gradients of texture and form. In the third set of experiments, 1 measured the temporal dependencies of perspective-disparity cue integration. Observers viewed a dichoptic pattern undergoing smooth temporal modulations or step changes in simulated slant and inclination specified by gradients of disparity and/or by perspective. Perspective and disparity were cornbined in four ways: disparity alone, perspective aione, perspective concordant with disparity, or perspective in conflict with disparity. Large pattemed displays providing strong linear perspective were seen according to perspective. With a static irregular texture. conflict was typically resolved according to disparity. This dominance of disparity built over tirne with initial depth typically seen according to perspective. With moving displays. however. perspective dominated the percept of surface slant or inclination. The hypothesis that pattems of vertical disparities are processed more slowly than equivalent pattems of horizontal disparities was only partiy confirmed. Vertical vergence is more sluggish than horizontal vergence. However, perceived slant and inclination showed sirnilar temporal limitations for gradients of both horizontal and vertical disparity. These limitations were related to disparity-perspective conflict. The temporal characteristics of the resolution of disparity-perspective conflict indicates that kinetic perspective is especially salient for human vision. This conclusion has important implications for experiments studying temporal factors in stereopsis in the presence of unchanging monocular cues. 1 would like to thank my supervisor Dr. Ian Howard for his suppon and encouragement. 1 greatly appreciate having the opportunity to work under his expert supervision. It would also like to thank the members of rny supervisory cornmittee, Drs. Ono, Harris and Steel for their suppon and constructive advice throughout the course of this research. Dr. Brian Rogers was a frequent visitor to our lab throughout this period and his expertise and collaboration in these experiments were greatly appreciated. 1 appreciate the generous suppon of NSERC and CRESTECH and am especially grateful to Dr. Ron Kruk and CAE Ltd. for their partnership in a CRESTECH Co-operative Research Award. 1 would like to thank Xueping Fang, Holly Bridge and Jim Zacher for their assistance with these experiments and for their many helpful comments. 1 am also grateful to Drs. Masayuki Sato, Hirohiko Kaneko. Byron Pierce, Masahiro Ishii. Christine Portfors, Mn. Toni Howard and Mr. Rob Gray for many discussions of my work and their related experiments. 1 would also like to express rny appreciation to the subjects who volunteered their time and to Drs. Tirnney, Davey and Wilcox for taking the time to examine my thesis. 1 would also like to thank Heather. Eric. Alan, Stephen. Gang. and Dalia for making the lab an enjoyable and intellectually stimulating place to work. 1 would like to thank the students and faculty associated with the York Centre for Vision Research as well as Teresa Manini and Jeff Laurence for their friendship and assistance. I would like especially like to thank my wife Jovie for her unconditional suppon and love that made it possible for me to complete this study. ABSTRACT ...................................................................................................................... IV ACKNOWLEDGEMENTS ..............................................................................................VI TABLE OF CONTENTS ................................................................................................. VII LIST OF FIGURES ......................................................................................................... X LIST OF TABLES ......................................................................................................XII LIST OF SYMBOLS AND ABBREVIATIONS ............................................................ XJII INTRODUCTION .......................................................................................................1 1 .1 Binocular Correspondence ......................................................................................I 1 -2 Patterns and Foms of Disparity .............................................................................. 7 1 2.1 Absolute and Zero-Order Disparities ............................................................ 12 1 .2.2 First-Order Disparity Patterns ....................................................................... 13 1.2.2.1 Slant about a Vertical Axis .................................................... 16 1.2.2.2 Inclination about a Horizontai Axis ....................................... 23 1.2.3 Higher-order Dispariries ................................................................................ 29 1.3 Binocular Vision and Vertical Dispaity ............................................................... 29 1.3.1 Fusion and Diplopia ...................................................................................... 30 1.3.2 Binocular Visual Direction ............................................................................ 32 1.3.3 Dichoptic Stimulation by Dissimilar Images ............................................. 31 1 .3.4 Vergence ........................................................................................................ 35 1.3.5
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