Effects of spatial configuration on contrast detection.

We studied spatial integration at low contrasts by testing the detection thresholds of multi-Gabor element displays, examining configuration parameters such as orientation uniformity, contour smoothness, continuity, spacing and relative phase. We find that detectability depends on stimulus geometry and is constrained by collinearity and proximity spatial relationships. For textures, thresholds decrease with local orientation uniformity. For a 'coherent' contour (e.g. smooth and continuous), thresholds decrease linearly with increased number of elements, on a log-log scale, with a slope of -1/4 (sensitivity S proportional to N1/4). However, for a 'non-coherent' contour (e.g. jagged or with spacing > 5 lambda) thresholds are only slightly affected by the number of patches. Similar behavior is observed for supra-threshold stimuli embedded in band-pass noise. These results suggest that contrast integration is primarily based on local mechanisms and constrained by contour properties. These local mechanisms are possibly mediated by lateral interactions in the primary visual cortex.