Shape and contour detection

Detectability of contours may be affected by long-range interactions between neurons in early stages of visual cortex. Specifically, neurons with receptive fields arrayed along the length of a contour may facilitate each other in a position- and orientation-dependent manner. Accordingly, the overall geometry of a contour should significantly influence both the strength of these long-range interactions and the contour's detectability. Psychophysical experiments measuring the detectability of sampled, curvilinear contours hidden by randomly-oriented and -positioned noise elements revealed two main findings. First, changes in direction of curvature degraded contour detectability. Second, the effect of changes in magnitude of curvature were predicted by the average of local curvature along the length of the contour. While the first result emphasizes the importance of uniform direction of curvature, the second result rules out penalties for deviation from circularity. (C) 1998 Elsevier Science Ltd. All rights reserved.