Region- and edge-based configurational effects in texture segmentation.

We have found a new configurational effect in texture segmentation. In addition to collinear facilitation at the edge, this effect results from contextual modulation within the texture-region, i.e. from texels not abutting the segmented edge. The largest facilitation was found when two conditions were fulfilled: (i) elements along the edge were parallel to the edge and collinear, (ii) elements in the texture-region were also collinear but non-parallel to the edge. We show that this facilitation occurs when there are groups of different orientation from the edge in the texture-region. We suggest two possible underlying mechanisms: either a region-based process that links collinear iso-oriented elements and locates the edge when the orientation changes, or else second-order filters tuned to orientation differences rather than orientation per se.