Purpose. Although it is commonly assumed that lateral spatial facilitation and contour integration have a common neural basis, we have previously shown some important differences between these two phenomena (Williams & Hess, JOSA,1998). Here we ask whether they have a common cortical site. For three subjects, we compared each task under monocular, binocular, dichoptic and stereoscopic viewing conditions to see if their respective sites are before or after binocular combination and/or disparity coding. Methods Using a standard 2AFC task, observers either indicated which of two interval containing high contrast flanking Gabors, contained a central Gabor target (lateral facilitation) or which of two intervals containing arrays of randomly oriented Gabor elements, contained a subset of Gabor elements aligned along a contour (the contour task). Results Lateral facilitation is not present under either dichoptic or stereoscopic viewing whereas contour integration operates under both conditions. Conclusion The processing site for lateral facilitation is different from that of contour integration. While both are cortical, the former involves monocular cells whereas the latter involves binocular as well as disparity-sensitive cells.

RFH is funded by NSERC grant #0GP0046528