BINOCULAR INTERACTION AND DISPARITY CODING IN AREA 19 OF VISUAL-CORTEX IN NORMAL AND SPLIT-CHIASM CATS

Binocular disparity, resulting from the projection of a three-dimensio nal object on the two spatially separated retinae, constitutes one of the principal cues for stereoscopic perception. The binocularity of ce lls in one hemisphere stems from two sources: (1) the ganglion cells i n the homonymous temporal and nasal hemiretinae and (2) the contralate ral hemisphere via the corpus callosum (CC). The objectives of this st udy were, on one hand, to determine whether disparity-sensitive cells are present in a ''higher order'' area, namely area 19 of the visual c ortex, of the cat and, on the other hand, to ascertain whether the CC contributes to the formation of these cells. As in areas 17-18, two ty pes of disparity-sensitive neurons were found: one type, showing maxim al interactive effects around zero disparity, responded with strong ex citation or inhibition when the stimuli presented independently to the two eyes were in register. These neurons are presumed to signal stimu li situated about the fixation plane. The other type, also made up of two subtypes of opposed valencies, gave maximum responses at one set o f disparities and inhibitory responses to the other set. These are pre sumed to signal stimuli situated in front of or behind the fixation pl ane. Unlike areas 17-18, however, disparity-sensitive cells in area 19 of the normal cat were less finely tuned and their proportion was low er. In the split-chiasm animal, very few cells were sensitive to dispa rity. These results, when coupled with behavioral data obtained with d estriate animals, indicate that (1) area 19 is probably less involved in the analysis of disparity information than area 17, (2) the dispari ty-sensitive neurons that arc sensitive to disparity are not involved in the resolution of very fine three-dimensional spatial detail, and ( 3) the CC only determines a limited number of these cells in the absen ce of normal binocular input.