CORTICAL AREA MT AND THE PERCEPTION OF STEREOSCOPIC DEPTH

Stereopsis is the perception of depth based on small positional differ ences between images formed on the two retinae (known as binocular dis parity). Neurons that respond selectively to binocular disparity were first described three decades ago(1,2), and have since been observed i n many visual areas of the primate brain, including V1, V2, V3, MT and MST3-8. Although disparity-selective neurons are thought to form the neural substrate for stereopsis, the mere existence of disparity-selec tive neurons does not guarantee that they contribute to stereoscopic d epth perception. Some disparity-selective neurons may play other roles , such as guiding vergence eye movementsg(9,10). Thus, the roles of di fferent visual areas in stereopsis remain poorly defined. Here we show that visual area MT is important in stereoscopic vision: electrical s timulation of clusters of disparity-selective MT neurons can bias perc eptual judgements of depth, and the bias is predictable from the dispa rity preference of neurons at the stimulation site. These results show that behaviourally relevant signals concerning stereoscopic depth are present in MT.