The Effect of Size Statistics of the Background Texture on Perceived Target Size

We investigated the effect of the size distribution statistics of background elements on the perceived size of a target. We manipulated the first, second, and third order statistics (i.e., mean, variance, and skewness) of the background element size distribution. We used a two-interval forced-choice paradigm to measure perceived target size at different background size distributions. In each trial, a standard disk, or target, was presented in one interval with a textured background and a comparison disk, on a blank background, in the other. The task for the observers was to determine which interval contained a larger disk. We measured the point of subjective equality for the perceived target size with a staircase procedure. The perceived target size decreased with the increment of mean background disk size. The variance and skewness of the background element size did not affect the perceived target size. Our results showed that only the first order statistics of the background modulated the perceived target size, not the higher order statistics. A computational model, in which the visual system extracts size information by averaging the responses of different size channels, whose response is modulated by the size of the background elements, can account for the results.