The effects of early and late monocular deprivation on binocular depth perception in cats.

Binocular and monocular depth discrimination thresholds were obtained from cats which had been monocularly deprived either from the time of natural eye opening or else at the age of 4 months. Among normal cats, binocular depth thresholds typically are very much better than monocular thresholds, allowing the inference that normal cats have good stereopsis. For the early-deprived animals in the present study, only those whose deprived eyes were opened by 30 days of age showed any binocular advantage. Deprivation periods lasting to 35 days or older completely eliminated the binocular superiority, with no sign of any recovery. These results provide behavioral evidence that binocular visual mechanisms are extremely susceptible to disruption and, unlike those underlying visual acuity, do not have the potential for recovery. The effect of deprivation imposed later in life was quite different. Three cats, deprived for 1, 2 or 3 months respectively, beginning at the age of 4 months, showed no deficits in binocular depth perception. This latter finding implies the existence of a sensitive period for stereopsis which is over completely by the age of 4 months.