Detectability of contours may be affected by long-range interactions betwee
n neurons in early stages of visual cortex. Specifically, neurons with rece
ptive fields arrayed along the length of a contour may facilitate each othe
r 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. Psychophysic
al experiments measuring the detectability of sampled, curvilinear contours
hidden by randomly-oriented and -positioned noise elements revealed two ma
in findings. First, changes in direction of curvature degraded contour dete
ctability. Second, the effect of changes in magnitude of curvature were pre
dicted by the average of local curvature along the length of the contour. W
hile the first result emphasizes the importance of uniform direction of cur
vature, the second result rules out penalties for deviation from circularit
y. (C) 1998 Elsevier Science Ltd. All rights reserved.