Striate, extrastriate and collicular processing of spatial disparity cues.

The spatial disparity sensitivity of single units in the primary visual cortex (17-18 border), in extrastriate area 19 and in the superficial layers of the superior colliculus of the cat brain were compared in the present study. Unit recordings were performed in paralyzed and anesthetized animals. Centrally located receptive fields were mapped, separated using prisms and then stimulated simultaneously using two luminous bars optimally adjusted to the size of the excitatory receptive fields. In the three regions studied, cells selective to spatial disparity were found and four classes of disparity sensitivity profiles emerged. Although the disparity sensitivity profiles of the cells in the three regions appeared to have the same general shape, selectivity was clearly different. Cells at the 17-18 border were sharply tuned, those of area 19 were not only less numerous but also less well tuned and collicular cells exhibited coarse selectivity. These differences in selectivity appear to be linked to the projection pattern of the X, Y and W systems to these regions and the roles that these cells might play in vision.