Perceptual grouping factors compete for salience

Both psychophysical and neurophysiological findings suggest that segmentation of a texture boundary based on orientation contrast is facilitated by contextual influences of elements collinear with, or parallel to, the boundary. Stimuli consisted of 8 × 8 test-matrices of Gabor elements all with the same orientation except those in one external row or column. After a short presentation interval, test matrices were masked by a matrix with no orientation cues. We measured the temporal threshold, defined as the test-matrix duration for discriminating (75% correct) the orientation of texture boundary. Experiment 1 showed that orientation discrimination of the row or column flanked by uniform texture was faster in configurations with 0° or 90° than with 45° or 135° orientation differences, although orientation contrast was fixed, confirming that segmentation is faster when local elements are collinear with the texture border. Unexpectedly (experiment 2), in the 0° or 90° configuration, there is a two-fold increase in thresholds when uniform texture in the matrix has the same orientation as the border. These results suggest that implicit processing of uniform texture on the basis of long-range lateral interactions occurs and interferes with the explicit process of texture boundary.