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
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