Role of visual cortex in interocular transfer in the cat

Abstract

The role of the visual cortex (areas 17, 19, and 19), with its preponderance of binocular cells, was investigated as a locus important for interocular transfer. Fourteen cats were tested for interocular transfer of a series of brightness and pattern discriminations in a two-choice, positive reinforcement paradigm. Three were controls. Eleven underwent manipulations designed to reduce the number of binocular cells in their visual cortices. The manipulations were: rearing with external strabismus induced by neonatal transection of one or both medial rectus muscles and/or surgery in adulthood to cut midbrain and forebrain commissures (but not the optic chiasm); and ablation of areas of visual cortex. Measurements of immediate transfer and relearning scores evaluated interocular transfer. Controls showed complete transfer of every discrimination, which contrasts to transfer failures of some tests seen with every experimental cat; three cats reared with strabismus and no adult surgery and three normally reared cats with adult brain lesions showed transfer deficits. These results suggest a role in interocular transfer for the binocular cells of the visual cortex. Two different methods to reduce their number resulted in transfer deficits. This implies that few binocular cells in the visual cortex can subserve good interocular transfer, or the geniculocortical regions outside of areas 17, 18, or 19 can subserve interocular transfer.