Luminance-contrast properties of texture-shape and texture-surround suppression of contour shape

Abstract

Studies have revealed that textures suppress the processing of the shapes of contours they surround. One manifestation of texture-surround suppression is the reduction in the magnitude of adaptation-induced contour-shape aftereffects when the adaptor contour is surrounded by a texture. Here we utilize this phenomenon to investigate the nature of the first-order inputs to texture-surround suppression of contour-shape, by examining its selectivity to luminance-polarity and the magnitude of luminance contrast. Stimuli were constructed from sinusoidal-shaped strings of either ‘bright’ or ‘dark’ elongated Gaussians. Observers adapted to pairs of contours and the aftereffect was measured as the shift in the apparent shape-frequency of subsequently presented test-contours. We found that the suppression of the contour-shape aftereffect by a surround texture made of similar contours was maximal when the adaptor’s center and surround contours were of the same polarity, revealing polarity specificity of the surround-suppression effect. We also measured the effect of varying the relative contrasts of the adaptor’s center and surround and found that the reduction in the contour-shape aftereffect was determined by the surround-to-center contrast ratio. Finally, we measured the selectivity to luminance polarity of the texture-shape aftereffect itself and found that it was reduced when the adaptors and tests were of opposite luminance-polarity. We conclude that texture-surround suppression of contour-shape, as well as texture-shape processing itself, depend on ‘On-Off’ luminance-polarity channel interactions. These selectivities may constitute an important neural substrate underlying efficient figure-ground segregation and image segmentation.