EFFECTS OF SPATIAL CONFIGURATION ON CONTRAST DETECTION

We studied spatial integration at low contrasts by testing the detecti on thresholds of multi-Gabor element displays, examining configuration parameters such as-orientation uniformity, contour smoothness, contin uity, spacing and relative phase. We find that detectability depends o n stimulus geometry and is constrained by collinearity and proximity s patial relationships. For textures, thresholds decrease with local ori entation uniformity. For a 'coherent' contour (e.g. smooth and continu ous), thresholds decrease linearly with increased number of elements, on a log-log scale, with a slope of - 1/4 (sensitivity S proportional to N-1/4). However, for a 'non-coherent' contour (e.g. jagged or with spacing > 5 lambda.) thresholds are only slightly affected by the numb er of patches. Similar behavior is observed for supra-threshold stimul i embedded in band-pass noise. These results suggest that contrast int egration is primarily based on local mechanisms and constrained by con tour properties. These local mechanisms are possibly mediated by later al interactions in the primary visual cortex. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.