The perceived contrast of texture patches embedded in natural images.

The visibility of an isolated simple stimulus is known to depend on its contrast. However, when such a stimulus is surrounded by other geometrically-simple stimuli, its perceived contrast can change markedly. Here, we examined whether such effects contribute to our perception of contrasts when we view real world scenes. We show that the perceived contrast of a luminance texture patch is suppressed when it is surrounded by images of real world scenes. We also show that the amount of this suppression depends on the spatial statistics of the surrounding images. We manipulated the second-order statistics of the images and found minimal suppression of perceived contrast at "un-natural" image statistics and maximal suppression at the characteristic statistics of natural images. This suggests that contrast gain control mechanisms in our visual system are optimally engaged when we view real world images.