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Reza Rajimehr; Anisotropic center-surround antagonism in visual motion perception. Journal of Vision 2005;5(8):133. doi: 10.1167/5.8.133.
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© ARVO (1962-2015); The Authors (2016-present)
Center-surround receptive field organization is an integral part of visual motion processing. These antagonistic structures, specifically those in MT area, are believed to be crucially involved in motion perception. Recently psychophysics has been exploited to demonstrate the perceptual consequence of center-surround motion opponency. Suppressive surround of the functional receptive fields, possibly in the area MT, renders the motion of a large high-contrast Gabor patch more difficult to discern. Since spatial antagonism (e.g. in MT) shows anisotropy at the neuronal level, it would be surprising to psychophysically clarify if and how anisotropic center-surround interactions are reflected at the behavioral level. In the first experiment we used large high-contrast elliptical Gabor patches and subjects were required to report its direction of motion. Stimulus duration threshold was significantly lower when the axis of elongation in the Gabor patch was perpendicular to the motion direction. This superiority effect was removed for elliptical Gabors with low contrast, small size or radial motion. These counterintuitive results could be fully explained by assuming two suppressive regions, which bilaterally surround an elongated functional receptive field. In the second experiment we used large high-contrast skewed Gabor patches and again measured the motion discriminability. Subjects had substantial difficulty in discriminating the motion signal when the motion direction was opposite to the direction of skewness in the Gabor. Low-contrast Gabors did not show such asymmetry in detection of motion directions. The results indicate that suppressive regions tend to spatially shift in the opposite direction of the Gabor's motion and, thus, providing a heterogeneous inhibitory surround with more strength in a single region on one side of the functional receptive field. The overall findings suggest some important conjectures to be addressed electrophysiologically.
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