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0.2 Vergence------·------· 12 Durham E-Theses The spatial averaging of disparities in brief, static random-dot stereograms Popple, Ariella Vered How to cite: Popple, Ariella Vered (1999) The spatial averaging of disparities in brief, static random-dot stereograms, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/4544/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk The Spatial Averaging of Disparities in Brief, Static Random-dot Stereograms by Ariella Vered Popple The copyright ofthis thesis rests with the author. No quotation from it should be pub! ished without the written consent of the author an information derived from it should be acknowledged. Submitted to the University ofDurham Department ofPsychology for the degree of Doctor ofPhilosophy 1999 2 4 AUG 1999 Ariella Vered Popple The spatial averaging of disparities in brief, static random-dot stereograms PhD. Thesis submitted to the University ofDurham Psychology Department 1999 Abstract Visual images from the two eyes are transmitted to the brain. Because the eyes are horizontally separated, there is a horizontal disparity between the two images. The amount of disparity between the images of a given point depends on the distance of that point from the viewer's point of fixation. A natural visual environment contains surfaces at many different depths. Therefore, the brain must process a spatial distribution of disparities. How are these disparities spatially put together? Brief (about 200 msec) static cyclopean random-dot stereograms were used as stimuli for vergence and depth discrimination to answer this question. The results indicated a large averaging region for vergence, and a smaller pooling region for depth discrimination. Vergence responded to the mean disparity of two transparent planes. When a disparate target was present in a fixation plane surround, vergence improved as target size was increased, with a saturation at 3-6 degrees. Depth discrimination thresholds improved with target size, reaching a minimum at 1-3 degrees, but increased for larger targets. Depth discrimination showed a dependence on the extent of a disparity pedestal surrounding the target, consistent with vergence facilitation. Vergence might, therefore, implement a coarse-to-fme reduction in binocular matching noise. Interocular decorrelation can be considered as multiple chance matches at different disparities. The spatial pooling limits found for disparity were replicated when interocular decorrelation was discriminated. The disparity of the random dots also influenced the apparent horizontal . alignment of neighbouring monocular lines. This fmding suggests that disparity averaging takes place at an early stage of visual processing. The following possible explanations were considered: 1) Disparities are detected in different spatial frequency channels (Marr and Poggio, 1979). 2) Second-order luminance patterns are matched between the two eyes using non-linear channels. 3) Secondary disparity filters process disparities extracted from linear filters. For: my grandfather: Jack Pepys, my father Aviam Heidecker, and my .brother Y annai: Heidecker. lfhey,did not live to s~e this fmished. Acknowledgments I wish to thank my husband, Mark, and my three children, Ulysses, Dante and Absalom for their enduring patience and support over the last three years. My grandmother, Rhoda Pepys, is owed a debt of gratitude for the financial assistance without which this would not have been possible. I am grateful to my supervisor, Prof. John Findlay, for his insight and enthusiasm during our frequent and often lengthy discussions. Past and present members of the psychology department are thanked for their assistance and encouragement, especially Dr. Harvey Smallman, my collaborator on chapter 2, who joined the meetings with Prof. Findlay and contributed knowledge and expertise as well as the use of his laboratory, and Dr. lain Gilchrist for practical help with the eye-trackers. This work was done with the support of a postgraduate studentship from the University of Durham Department of Psychology. Finally, many thanks to my tireless fellow postgraduates and other volunteer subjects who participated in the experiments. iii Contents Figures and Tables------------ ------vi Dec Iarati on --------------------------------------------------------------------------------------------------------- vi i Statement of copyright------------------------------------------------------------------------------------------- vi ii () l~lrFt()[)lJC:lrl()~-------------------------------------------------------------------------------1 How the brain sees with two eyes--- 1 0.0 Summary and objectives---------- 1 0.1 The geometry of binocular vision------·----- 3 0.2 Vergence--- ----·------------------------· 12 0.3 Stereopsis--- ------------------------ 19 0.4 Visual direction -----------------26 0.5 Neurophysiological background---- ----30 0.6 How does the brain see with two eyes?-----· 35 <:ti~f»lri:Fl 1 ················--~-----------------------------------------------------------------~9 Initial horizontal vergence is stimulated by the weighted mean disparity of two transparent planes39 1. 0 Abstract--------------------------------------------------------------------------------------------------------- 3 9 1.1 Selective replication of Mallot et al. ( 1995, 1996) -------------------------------------------------------- 40 1.2 Disparity integration of overlapping planes --------------------------------------------------------------- 53 C:ti~F»lrE:Ft 2 ------------------------------------------------------------------------------------~7 The area of spatial averaging for initial horizontal disparity vergence 57 2 .0 Abstract--------------------------------------------------------------------------------------------------------- 57 2.1 The pooling region for initial vergence -------------------------------------------------------------------- 58 2.2 Disparity and display size have little effect on the disparity averaging area for initial vergence--- 75 2.3 Dot size has little effect on the disparity averaging area for initial vergence ------------------------- 80 C:ti~F»1rE:Fl :3 ------------------------------------------------------------------------------------~!5 Stereoaculty - spatial integration and the effects of vergence 85 3. 0 Abstract--------------------------------------------------------------------------------------------------------- 8 5 3.1 The effect of random-dot disc diameter on stereoacuity threshold------------------------------------- 86 3.2 'Coarse to fine' cyclopean processing---------------------------------------------------------------------- 93 3.3 Pedestal size effect is not explained by lateral interactions---------------------------------------------100 CHAPTER 4 ····························--·········---···-·············--········-············4 09 The spatial integration of interocular correlation 109 4.0 Abstract-------------------------------------------------------------------------------------------------------- 109 4.1 The effect of surround correlation on vergence integration -------------------------------------------- 110 iv 4.2 Interocular integration of initial vergence triggered by non-fused stimuli ---------------------------118 4.3 Integrating correlated and uncorrelated dots at the same location------------------------------------- 123 4.4 Integrating neighbouring correlated and uncorrelated regions----------------------------------------- 128 4.5 Spatial limitations of decorrelation hyperacuity --------------------------------------------------------- 132 C:ti~F»lrE:~ 5 --------------------------------------------------···------------------------------438 Visual direction and local disparity integration ----------138 5 .0 Abstract-------------------------------------------------------------------------------------------------------- 13 8 5.1 Is monocular visual direction computed by binocular neurones?-------------------------------------- 139 5.2 A comparison between subjective and objective estimates of initial vergence ----------------------149 6 [)I~C:lJ~~IC>~ -------------------------------------------------------------------------------462 How are disparities integrated? ----162 6.0 Summary------------------------------------------------------------------------------------------------------ 162 6.1 Theories of disparity integration--------------------------------------------------------------------------- 163 6.2 Theories and thesis------------------------------------------------------------------------------------------- 172 6.3 Suggestions for further studies----------------------------------------------------------------------------- 176 6.4 Conclusion---------------------------------------------------------------------------------------------------- 182 RE FE RE~ C: E~ --------------------------------------------------------------------------------4
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