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Duje Tadin; Center-surround interactions in visual motion perception. Journal of Vision 2011;11(11):31. doi: 10.1167/11.11.31.
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© ARVO (1962-2015); The Authors (2016-present)
Visual processing faces two conflicting demands: integration and segmentation (Braddick, 1993). In motion, spatial integration is required by the noisy inputs and local velocity ambiguities. Local velocity differences, however, provide key segregation information. We demonstrated that the balance between integrating and differentiating processes is not fixed, but depends on visual conditions: At low-contrast, direction discriminations improve with increasing size – a result indicating spatial summation of motion signals. At high-contrast, however, motion discriminations worsen as the stimulus size increases – a result we describe as spatial suppression (Tadin et al., 2003). This adaptive integration of motion signals over space might be vision's way of dealing with the contrasting requirements of integration and segmentation, where suppressive mechanisms operate only when the sensory input is sufficiently strong to guarantee visibility. In subsequent studies, we have replicated and expanded these results using a range of methods, including TMS, temporal reverse correlation, reaction times, motion-aftereffect, binocular rivalry and modeling. Based on the converging evidence, we show that these psychophysical results could be linked to suppressive center-surround receptive fields, such as those in area MT.
What are functional roles of spatial suppression? Special population studies revealed that spatial suppression is weaker in elderly and schizophrenic patients – a result responsible for their paradoxically better-than-normal performance in some conditions. Moreover, these subjects also exhibit deficits in figure-ground segregation, suggesting a possible functional connection. In a recent study, we directly addressed this possibility and report experimental evidence for a functional link between surround suppression and motion segregation.
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