Early vision and texture perception.

Texture perception has frequently been studied using textures constructed by repeated placement of micropatterns or texture elements. Theories have been developed to explain the discriminability of such textures in terms of specific features within the micropatterns themselves. For example, Beck observed that a region filled with vertical Ts is readily distinguished from one filled with tilted Ts but not from one filled with vertical Ls. He attributed this to the different distribution of oriented line segments present in the former case but not in the latter. However, Bergen and Julesz found that a region of randomly oriented Xs segregated from one filled with randomly oriented Ls, in spite of the identical distribution of oriented line segments in the two cases. They suggested that this discrimination might be based on the density of such features as terminators, corners, and intersections within the patterns. We note here that simpler, lower-level mechanisms tuned for size may be sufficient to explain this discrimination. We tested this by varying the relative sizes of the Xs and the Ls; when they produce equal responses in size-tuned mechanisms they are hard to discriminate, and when they produce different size-tuned responses they are easy to discriminate.