Eeects of Spatial Connguration on Contrast Detection Eeects of Spatial Connguration on Contrast Detection

We studied spatial integration at low contrasts by testing the detection thresholds of multi Gabor element displays, examining connguration parameters such as orientation uniformity, contour smoothness, continuity, spacing and relative phase. We nd that detectability depends on stimulus geometry and is constrained by collinearity and proximity spatial relations. For a \coherent" connguration (e.g. smooth and continuous contour) thresholds decrease linearly with increased number of elements, on a log-log scale, as expected from probability summation (q = 4). However, for a \non-coherent" connguration (e.g. spacing > 4 or jagged contour) thresholds are little aaected by the number of patches. Similar behavior is observed for supra-threshold stimuli embedded in bandpass noise. These results suggest that contrast integration is primarily based on local mechanisms and constrained by contour properties. These local mechanism are possibly mediated by lateral interactions in the primary visual cortex.