On the detection of salient contours

When visual space is densely populated by elements of random orientation, elements which happen to be aligned may form a perceptually salient 'contour' (Field et al., 1993; Kovacs and Julesz, 1993). Here we further characterize human performance for detecting this type of Gestalt grouping. We find that detectability of salient contours reaches a plateau when they comprise at least 10 elements and are presented for at least 200 ms. It has been suggested that the detection of salient contours is mediated by the intrinsic connectivity of striate cortex and several computational models have been formulated on this basis. The present data provide a benchmark against which such models can be evaluated.