SPATIAL DISPARITY CODING IN THE SUPERIOR COLLICULUS OF THE CAT

Cells in the superficial layers of the superior colliculus of the cat have mainly binocular receptive fields. The aim of the present experim ent was to investigate the sensitivity of these cells to horizontal sp atial disparity. Unit recordings were carried out in the superficial l ayers of the superior colliculus of paralyzed and anesthetized cats, C entrally located receptive fields were mapped, separated using prisms, and then stimulated simultaneously using two luminous bars optimally adjusted to the size of the excitatory region of the receptive fields. Only binocular cells were tested, and 65% of these units were found t o be sensitive to spatial disparities. Some cells (20%) were clearly i nsensitive to spatial disparity and the remaining 15% showed complex, unclassifiable interactions. The sensitive cells could be divided into four classes based on their disparity-sensitivity profiles: 38% showe d excitatory interactions, whereas 9% showed inhibitory interactions. Moreover, 11% and 7% of the cells responded, respectively, to crossed or uncrossed disparities, and were classified as near cells and far ce lls. Whereas the general shapes of the sensitivity profiles were simil ar to those of cells in areas 17-18, selectivity in the superior colli culus was significantly coarser. The superficial layers of the superio r colliculus project topographically to the deep layers of the superio r colliculus, which are known to contain circuits involved in the cont rol of ocular movements. The results thus suggest that disparity-sensi tive cells of the superior colliculus could feed information to these oculomotor neurons, allowing for the localization and fixation of obje cts on the appropriate plane of vision.