Perceiving textures: beyond filtering.

Classical texture segregation theory and current visual filtering models suggest that rapid texture segregation is determined by the properties of early cortical filtering. To examine this assumption, we manipulated the binocular disparity of texture elements (an L vs a bar) relative to adjoining squares. Such a manipulation has little effect on the early cortical filtered representations of the stimuli but can have a strong influence on surface representation. In particular, it can determine whether an image patch is seen as a distinct surface, in front, or part of a larger occluded surface, in back. When seen as part of an occluded surface, the distinctive shape of each texture element is reduced. Accordingly, we found that texture discrimination performance was impaired when the texture elements had uncrossed disparities ("back" case). Additional experiments indicated that this result was not due to the disparity manipulation alone, but occurred only when each texture element was perceived as part of an occluded surface. We conclude that in rapid texture discrimination, the visual system cannot ignore information regarding surface layout. This suggests that for purposes of texture perception, either: (a) the visual system has no access to the filtered image or (b) one cannot entertain the concept of a filtered image uninfluenced by higher order surface processing.