Common properties of visual segmentation

Recent experiments on the psychophysics of texture segmentation have produced several interesting observations that provide a useful basis for discussing the underlying neuronal mechanisms. Segmentation is predominantly achieved by analysis of local differences across a texture border, not global similarities. This suggests the involvement of a local, orientation contrast-sensitive mechanism similar to lateral inhibition in the retina. For segmentation to occur, orientation differences at the texture border must be increased when the overall orientation variation in the background of a pattern is raised. Similar properties are found for other visual clues that provide perceptual segregation. For motion, segmentation is based on the detection of local differences between areas rather than the analysis of global motion coherence within areas. Such local differences must be increased for successful segmentation when background movement is made non-uniform. Colour, luminance and binocular disparity behave in a similar way, suggesting a general role for feature contrast in visual segmentation.