Behavioral studies on the effect of abnormal early visual experience in monkeys: spatial modulation sensitivity.

Spatial modulation sensitivity functions have been investigated by behavioral methods in two monkeys reared with normal visual experience and 12 monkeys reared with abnormal, early visual experience. Experimental treatments were initiated when the animals were approximately one month of age. Two monkeys were each treated with one of the following procedures: (1) long-term monocular lid suture, (2) short-term monocular lid suture, (3) surgically induced esotropia, (4) surgically induced exotropia, (5) optical dissociation of binocular vision with ophthalmic prisms, or (6) chronic monocular cycloplegia. The results of the studies showed a severe loss of contrast sensitivity of the treated eyes compared to the control eyes for monkeys reared with monocular lid suture or surgically induced esotropia. Surgically induced exotropia resulted in a moderate reduction in sensitivity of the deviated eye while optical dissociation resulted in a mild reduction in sensitivity of one eye compared to the other. One of the two monkeys reared for seven months with chronic monocular cycloplegia had a relative reduction in contrast sensitivity of the treated eye, but the other monkey had equal sensitivities in the two eyes. However, binocular summation experiments showed that even though the relative difference between the monocular sensitivities was small or absent for the monkeys reared with optical dissociation or chronic monocular cycloplegia, none of them demonstrated binocular vision in these experiments.