A pattern with a horizontal luminance profile described by the difference of Gaussians (DOG) was viewed under conditions of retinal image stabilization. When a uniform increment was applied after the image had disappeared, the pattern reappeared, but with the reversed phase. This phenomenon of apparent phase reversal (APR) is indicative of changes in local sensitivity. It was studied as a function of the time at which the increment was applied and the space constant of the DOG pattern. It was found that the threshold increment necessary to evoke an APR was an exponential function of time. A slight dependence on the spatial dimensions of the stimulus was also demonstrated. The data were examined according to a model of spatial vision that includes a gain that is inversely proportional to a spatially and temporally filtered version of the stimulus. The data provided estimates of the time constant and the spatial extent of the gain mechanism.
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