Understanding the Spatial Characteristics of Interocular Suppression and Functional Stereopsis



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Purpose: To study the effect of stimuli parameters in two different binocular phenomena; interocular suppression and stereopsis. We quantified the spatial extent of suppression and assessed depth perception as a function of various stimulus parameters, using Random Dot Stereograms (RDS) and virtual reality (VR) environment.

Methods: Six experiments are described. (1) We mapped the spatial extent of suppression during binocular rivalry using Difference of Gaussian stimuli at different spatial frequency (SF), contrast, and luminance (2) With the same paradigm, interocular difference in SF, contrast and luminance stimuli were used to model the deficits in anisometropic amblyopia. (3) We developed a new stereo letter stereo test that assesses stereopsis at far and near, crossed and uncrossed disparity varying in letter sizes corresponding to different SFs. (4) We investigated the effect of SF, contrast, and blur in the range of functional stereopsis (lower to upper limit). (5) In a VR environment, we assessed the effect of figure-background information on a depth discrimination task using bandpass noise patterns at different SFs. (6) We further isolated the individual contributions of textures and edges in the VR depth discrimination task.

Results: (1) The suppression zone decreased with higher SFs and lower contrast, with a larger size in the horizontal dimension. (2) With unequal SFs, the zone changed in an additive relationship between the two eyes. Unequal stimulus contrast had a monotonic effect. (3) The disparity sensitivity function had an inverted U shape, with decreasing sensitivity for smaller letters. Subjects had better far stereopsis than near, and were better with crossed versus uncrossed disparity. (4) The range of stereopsis decreased with higher SF, lower contrast, and higher amount of blur. (5) Depth discrimination was better with a textured target and best at middle SFs. The background also affected the performance. (6) Edges helped in breaking camouflage and were crucial with a non-textured target.

Conclusion: We demonstrated that the spatial extent of suppression varies according to stimulus parameters. The spatial characteristics of the target and background also affect disparity sensitivity and depth discrimination in complex ways.



Binocular rivalry, Suppression, Depth perception, Virtual reality


Portions of this document appear in: Lew, Wei Hau, Scott B. Stevenson, and Daniel R. Coates. "Stimulus dependence of interocular suppression." Scientific Reports 11, no. 1 (2021): 9309; and in: Lew, Wei Hau, and Daniel R. Coates. "Assessment of depth perception with a comprehensive disparity defined letter test: A pilot study." Plos one 17, no. 8 (2022): e0271881.