INTEGRATION OF MOTION AND STEREOPSIS IN MIDDLE TEMPORAL CORTICAL AREAOF MACAQUES

THE primate visual system incorporates a highly specialized subsystem for the analysis of motion in the visual field(1-6). A key element of this subsystem is the middle temporal (MT) cortical area, which contai ns a majority of direction-selective neurons(1-3). MT neurons are also selective for binocular disparity (depth), which is perplexing given that they are not sensitive to motion through depth(7). What is the ro le of disparity in MT? Our data suggest an important link between disp arity and transparent motion detection. Motion signals in different di rections tend to inhibit each other within a given MT receptive field( 8). This inhibition has an averaging effect which minimizes MT respons es to random motion signals created by light intensity changes and oth er non-motion stimuli (motion noise)9. But, in the absence of disparit y cues, inhibition may also occur between surfaces moving in different directions through the same part of the visual field (transparent mot ion), thus impairing the detection of either surface. Here we show tha t inhibition in MT occurs mainly between motion signals with similar d isparities. Transparent surface movements at different depths are thus represented independently in MT (that is, without inhibiting each oth er) whereas spurious motion signals from a given surface tend to cance l out. To our knowledge, these results provide the first evidence for a functional integration of motion and disparity in MT.