Spatial-frequency tuning of visual contour integration

We examine the mechanism that subserves visual contour detection and particularly its tuning for the spatial frequency of contour components. The measured the detection of contours composed of Gabor micropatterns within a held of randomly oriented distracter elements. Distracters were randomly assigned one of two spatial frequencies, and elements lying along the contour alternated between these values. We report that the degree of tolerable spatial-frequency difference between successive contour elements is inversely proportional to the orientation difference between them. Spatial-frequency tuning (half-width at half-height) for straight contours is similar to 1.3 octaves but, for contours with a 30 degrees difference between successive elements, drops to similar to 0.7 octaves. Integration of curved contours operates at a narrower bandwidth. Much orientation information in natural images arises from edges, and we propose that this narrowing of tuning is related to the reduction in interscale support that accompanies increasing edge curvature. (C) 1998 Optical Society of America.