CONSTRAINTS ON LONG-RANGE INTERACTIONS MEDIATING CONTOUR-DETECTION

Contour detection may be mediated by lateral interactions between neig hboring cortical neurons whose receptive fields have collinear axes of preferred orientation, This hypothesis was tested in psychophysical e xperiments and computer simulations using a contour detection task in which observers searched for groups of Gabor patches that followed spa tially extended contour paths embedded in noise consisting of several hundred Gabor patches with random positions and orientations, The orie ntation-selective units in the simulated neural network were linked by facilitatory interconnections whose strength depended on the geometry (distance, curvature, change in curvature) of smooth curves connectin g the orientation axes of units in a pair,vise fashion, Psychophysical detection performance was much higher for contour signal groups that followed closed rather than open-ended paths, However, just two sudden changes in orientation of neighboring Gabor patch elements in closed- path contours reduced detection performance to the same levels obtaine d with open-ended contours, These psychophysical data agreed with the results of the neural network simulations, Furthermore, the simulation s also accounted for previous findings that removal of a single Gabor patch element from a closed-path contour group significantly degraded detection performance, We conclude that closure alone is not sufficien t to enhance the visibility of a contour. However, if a closed contour meets certain geometric constraints, then lateral interactions based on these constraints can generate facilitation that reverberates aroun d the closed path, thereby enhancing the contour's visibility. (C) 199 8 Elsevier Science Ltd. All rights reserved.