Emergence of a contrast-invariant representation of naturalistic texture in macaque visual cortex.

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Single neurons in visual cortex respond selectively to multiple stimulus dimensions, so signals from single neurons cannot distinguish changes in one dimension from changes in another. We measured responses from simultaneously recorded neural populations in three hierarchically linked visual areas - V1, V2, and V4 - using texture stimuli that varied in two dimensions, contrast and naturalistic image structure. We used linear decoding methods to extract information about each dimension. In all three areas, contrast could be decoded independently of image structure. Only in V4, however, could image structure be decoded independently of contrast. The reason is that selectivity for texture and contrast in V4 was much more diverse than in V1 or V2. This heterogeneity allows V4 to faithfully represent naturalistic image structure independent of contrast.