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Chao Han, Wanyi Huang, Zijiang J He, Teng Leng Ooi; The role of boundary contours in suprathreshold binocular perception of contrast and spatial phase. Journal of Vision 2019;19(10):223. doi: https://doi.org/10.1167/19.10.223.
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Boundary contours play a crucial role in representing smooth, texture-free binocular surfaces. However, less is known about their influence on perceived binocular contrast and spatial phase of surfaces with textures, such as grating surfaces. We investigated this by designing two generic binocular surface stimuli differing in boundary contour content (supplemental material). In Experiment 1, the (a) binocular boundary contour (BBC) stimulus had a central square region (1×1 deg) surrounded by a larger background (8×8 deg) with 3 cpd sinusoidal grating. The central square was created by phase-shifting the central grating region (20.0% contrast) 45 deg above the green horizontal reference lines in one half-image, and 45 deg below in the other half-image (50.1% contrast). The (b) monocular boundary contour (MBC) stimulus had a central square region with 20.0% contrast in one half-image (phase-shifted 90 deg relative to surrounding background grating), while the other half-image comprised the background grating with 50.1% contrast. We measured perceived binocular contrast of the central square region by varying contrast (QUEST) of a comparison stimulus. We found perceived contrast of the BBC stimulus reflected that of the grating patch with high contrast (50.1%). But surprisingly, perceived contrast of the MBC stimulus reflected that of the MBC grating patch (20.0%), rather than the high contrast (50.1%) of the uniform grating background in the fellow eye. In Experiment 2, both stimuli’s contrast was set at 31.6%. We measured perceived spatial phase of the grating patch using the staircase method. We also found the spatial phase of the MBC grating patch had a dominant role in determining perceived spatial phase. However, for the BBC stimulus, perceived spatial phase of the central grating depended on both dichoptic grating patches. Overall, both experiments indicate MBC renders the grating patch dominant over the uniform grating without boundary contour for binocular surface representation.
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