Selective loss of binocular depth perception after ablation of cat visual cortex

Abstract

The massive visual projection to cortical areas 17 and 18 (striate and parastriate cortex) of the cat strongly suggests that these structures have a major role in visual processing. It is therefore paradoxical that ablation of these areas has been reported to result in very trivial deficits in their visual perception and behaviour^1,2. In contrast to humans and monkeys, which show profound visual deficits after ablation of the visual cortex^3–6, cats with similar lesions show essentially normal visual behaviour and are able to discriminate complex visual patterns. The only apparent effect of cortical lesions is a mild impairment of the visual acuity for gratings and a possibly greater reduction of vernier acuity⁷. In the past, the functional deficits resulting from lesions or ablations of various cortical structures have provided important clues to the function of many cortical areas, but recently a more detailed picture has emerged from electro-physiological studies of the properties of their constituent neurones. A striking aspect of most visual cortical cells in both cat and monkey is their specificity for horizontal retinal disparity^8–10, the detection of which is a prerequisite for stereopsis¹¹. This suggests that the visual cortex may play a major part in mediating stereopsis. We report here that ablation of cortical areas 17 and 18 in the cat results in severe selective deficits in binocular depth perception consistent with a loss of stereopsis.