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S. A. Collier, A. B. Cobo-Lewis; Contrast gain control moderates bias of perceived motion in Type 2 plaids. Journal of Vision 2006;6(6):1044. doi: 10.1167/6.6.1044.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous research has supported a Bayesian model of motion combination for the perception of moving Type 2 plaids. When one component grating provides a more reliable motion signal than the other, perceived direction of the plaid is biased in the direction of the more reliable grating. Our previous research offered evidence for 1) bias of perceived plaid direction toward the grating of higher spatial frequency (SF), 2) bias of perceived plaid direction toward the grating of higher contrast when overall contrast was low, with little or no bias toward the grating of higher contrast when overall contrast was high. We hypothesized that contrast gain control was obscuring the effect of contrast-ratio manipulation. Our current research provides an analysis of the effect of contrast ratio under differing overall contrast conditions. Methods: Subjects viewed Type 2 plaids whose component gratings drifted in directions separated by 15 degrees and whose speeds differed by a factor of sqrt(1.5). We manipulated the ratio of the gratings' contrast in conditions with different baseline contrasts. Subjects pointed an arrow in the direction of the perceived drift of the plaid. Results: The effect of contrast-ratio manipulation differed with baseline contrast. Under high-contrast conditions there is little effect of contrast-ratio manipulation. Under moderate and low contrast conditions, the perceived drift of the plaid pattern becomes biased in the direction of the higher-contrast component. These results offer evidence for an effect of contrast gain control in moderating the bias of perceived plaid motion.
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