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Adrien Chopin, Pascal Mamassian, Randolph Blake; Transition between stereopsis and binocular rivalry is based on perceived, rather than physical, orientation. Journal of Vision 2011;11(11):301. doi: 10.1167/11.11.301.
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© ARVO (1962-2015); The Authors (2016-present)
When dichoptically viewed gratings differ slightly in orientation, they can still combine binocularly to yield perception of a surface slanted in depth. With larger differences in orientation disparity, fusion gives way to binocular rivalry characterized by perceptual alternations between the left and right eye gratings, with no depth. Can this transition point between stereo-fusion and rivalry be shifted by induction of illusory shifts in perceived orientation? We addressed this question using a variant of the Zöllner illusion: When parallel short lines (inducers) are added to a near-vertical grating, repulsion appears between inducer and grating orientations. If stereopsis uses the perceived illusory orientations, vertical inducers should increase the perceived orientation disparity of the gratings and horizontal inducers should decrease it. In contrast, if physical orientations are used, inducers should have no effect on the orientation disparity. Observers were asked to judge the slant of a grating composed of near-vertical contours. Orientation disparity was varied adaptively to estimate the transition in orientation disparity between stereo-fusion and rivalry. If this transition depends on perceived, rather than physical, orientation, gratings should become more often rivalrous with vertical inducers and more often fused with horizontal inducers. Seven of eight observers (six na&ıuml;ve) exhibited reliable differences in this depth/rivalry transition point between vertical and horizontal inducer conditions, indicating that rivalry and stereopsis can be generated from illusory orientations. A second experiment in which observers reported their subjective experiences of rivalry corroborated this finding. The magnitude of that difference was approximately twice the classical Zöllner illusion: it suggests that shifts in illusory orientation arise at a monocular level, before the resolution of rivalry and stereopsis, and adds up between eyes. We are currently investigating whether comparable interactions occur when interocular differences are induced in motion direction, which is believed to be represented at binocular levels of processing.
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