Spatial localization in cats reared with strabismus.

1. The capacity for judging the location of an object relative to the body (egocentric localization) was assessed in cats by measuring the landing position attained when the cat jumped toward a platform viewed from a known distance. 2. Normal cats and kittens land at center of the platform when using one eye or both. In contrast, nine animals tested immediately after tenotomy of the medial rectus muscle of one eye all landed consistently off-center when using the operated eye. The direction of the error was predictable from the assumption that the cat was unaware of the eye's deviation from its natural position. Thus, proprioceptive reafference is not capable, under these conditions, of supporting an accurate awareness of eye position. 3. After initial testing, all cats were maintained in a normal environment with both eyes open and were tested intermittently. Jumps guided by the deviated eye became accurate over a period of weeks in kittens younger than 4 mo. In contrast, behavioral adjustment in older kittens required many months. An adult cat displayed almost no adjustment over a period of 9 mo. 4. Five additional kittens were first tested several months after the onset of strabismus. These animals manifested accurate use of the operated eye from the first trial onward. Therefore, acquisition of accurate use of the deviated eye is not dependent on repeated testing. 5. Two kittens subjected to early exodeviation of one eye displayed a reduced capacity for adjustment when subjected to late exodeviation of the second eye. Thus, changes in neural function resulting from early strabismus (for instance, the loss of binocular connectivity in striate cortex) do not produce persistent behavioral flexibility. 6. In two strabismic kittens with a fully developed compensatory adjustment of monocular egocentric localization, the capacity for judging the relative location of two objects viewed simultaneously through separate eyes was assessed through use of a two-choice visual discrimination paradigm. One animal made predictable systematic errors, while the other exhibited correct judgments. Thus, it appears that a compensatory shift of retinal correspondence may occur in some strabismic kittens, but that such a change is not necessary for accurate use of the deviated eye in monocular visual guidance. 7. A number of observations are described that tend to indicate that cats reared with strabismus continue to use both the deviated and the nondeviated eye for visual guidance under binocular viewing conditions, unlike many human strabismics.