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Yong Su, Teng Leng Ooi, Zijiang He; Incompatible local features are unnecessary for binocular suppression. Journal of Vision 2008;8(6):242. doi: 10.1167/8.6.242.
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It is generally assumed that binocular suppression is induced when two half-images have incompatible local features (e.g., orthogonal gratings). We report here a new observation where binocular suppression could be induced by half-images with similar local features. Experiment 1 employed a stereo display whose one half-image had a 3cpd vertical grating (4.5×4.5deg) and the other half-image had a 1.5deg disc with vertical grating that was surrounded by a spatially phase-shifted vertical grating (4.5×4.5deg). The phase shift created a monocular boundary contour (MBC) around the disc, and led to the percept of a stable disc separated in depth from the surrounding grating. We measured the increment contrast threshold of a monocular Gaussian probe upon the vertical grating at varying contrast levels (0.8–1.6 log unit) (TvC function). We found the TvC function to be higher in the eye viewing the vertical grating alone than in the eye viewing the vertical grating with the MBC disc, indicating suppression of the former eye (despite the two half-images having similar local features). Corroborating this, Experiment 2 using a spatial frequency difference (3 vs. 3.5cpd) to create the monocular MBC disc with vertical grating, also showed suppression in the other eye viewing only the vertical grating. These findings suggest the interocular inhibitory and stereo processes together form a stable 3-D percept, in which the grating within the disc matches with the vertical grating in the other eye to obtain depth while suppressing it from visual awareness. Finally, confirming the co-existence of binocular suppression and depth perception, we demonstrated that a monocular green grating disc on a binocular red grating background is mostly perceived at a different depth in green, rather than in a red/green color mixture or color rivalry. We conclude that besides local features, boundary contour information can trigger binocular suppression while supporting depth.
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