Visual response saturation to orientation contrast in the perception of texture boundary.

We analyzed how the visual response to orientation modulation in texture patterns varied as a function of the magnitude of orientation contrast. Using a contrast-discrimination technique, we measured threshold increments of orientation contrast (the orientation contrast required for discriminating between two textures) at various pedestal-orientation contrasts. The orientation-contrast-response function estimated for a step-orientation contrast, which produces a vivid percept of surface boundaries, saturated at approximately 30 degrees (experiment 1). The saturation was still evident even when the strength of the step-orientation contrast was reduced by orientation noise (experiment 2), but no strong saturation was found for textures that did not produce a vivid percept of surface boundaries (experiment 3). These results are consistent with the notion that orientation-based texture segregation involves the generation of a neural representation of the surface boundary whose strength is nearly independent of the magnitude of orientation contrast.