Co-circularity opponency in visual texture.

It is well known that the human visual system is sensitive to co-circularity among oriented edges, which are ubiquitous features of object contours. Here, we report a novel aftereffect in which the appearance of a texture is dramatically altered after adaptation to a texture composed of elements with co-circular structure. Following prolonged viewing of a texture made of pairs of adjacent Gabor elements arranged to form obtuse angle co-circular pairs, i.e. shallow curves, a subsequently viewed random texture appears to be composed of acute angle, i.e. near-parallel pairs. Conversely, adaptation to a texture made of parallel pairs causes a random texture to appear to be composed of shallow curves. This suggests that mechanisms sensitive to co-circularity are organized in an opponent manner, with one pole sensitive to shallow curves the other parallel shapes. This notion was tested further in a non-adaptation experiment in which co-circular and non-co-circular Gabor pairs were mixed within a single texture. Results revealed summation between pairs that fell on one side of the opponent continuum, and cancellation between pairs that fell on opposite sides of the continuum. Taken together these results support opponent interactions between mechanisms sensitive to pairwise co-circular texture features.