Motion direction, speed and orientation in binocular matching

The spatial differences between the images seen by the two eyes, called bin ocular disparities, can be used to recover the volumetric (three-dimensiona l) aspects of a scene. The computation of disparity depends upon the correc t identification of corresponding features in the two images. Understanding what image features are used by the brain to solve this matching problem i s one of the main issues in stereoscopic vision(1). Many cortical neurons i n visual areas V1 (ref. 2), MT (refs 3, 4) and MST (refs 5, 6) that are tun ed to binocular disparity are also tuned to orientation, motion direction a nd speed. Although psychophysical work has shown that motion direction(7) c an facilitate binocular matching, the psychophysical literature on the role of orientation is mixed(8,9), and it has been argued that speed difference s are ineffective in aiding correspondence(7). Here we use a different psyc hophysical paradigm to show that the visual system uses similarities in ori entation, motion direction and speed to achieve binocular correspondence. T hese results indicate that cells that multiplex orientation, motion directi on, speed and binocular disparity may help to solve the binocular matching problem.