Change detection is easier at texture border bars when they are parallel to the border: evidence for V1 mechanisms of bottom-up salience

A vertical bar is salient among horizontal ones by orientation contrast, and, traditionally, bottom up salience is viewed as caused only by feature contrast. Recently, it has been proposed that the primary visual cortex (V1) creates a bottom-up salience map in its outputs, which depends on direct inputs and on contextual inputs by intra-cortical interactions (Li Zhaoping, 2002 Trends in Cognitive Sciences 6 9-16). Since the interactions include iso-feature (eg iso-orientation) suppression, responsible for salience by feature contrast, and collinear facilitation, the V1 proposal predicts that collinear grouping contributes to salience additionally. Accordingly, in orientation textures, texture bars are more salient near texture borders owing to orientation contrast, and are even more salient when they are additionally parallel to the border by collinear grouping. We show that colour changes in texture bars are more detectable when the bars are parallel to the texture border. Since changes are more detectable at salient locations, our finding supports V1 mechanisms for bottom-up salience.