Behavioral and morphological evidence for binocular competition in the postnatal development of the dog's visual system.

Two normally-reared dogs and five dogs reared with monocular eyelid closure were studied. The two normal dogs and three of the deprived dogs were tested with a perimetry technique for the extent of behavioral visual field, and all of the dogs were studied histologically to determine the size of cell somata in the lateral geniculate nucleus. Behaviorally, the normal dogs saw with each eye approximately from 120 degrees ipsilateral to 30 degrees contralateral. The deprived dogs had a normal field of view for the non-deprived eye, but with the deprived eye they saw only in the monocular segment (i.e., approximately 120 degrees to 30 degrees ipsilateral). Histologically, geniculate cells in the monocular segment of deprived dogs were of normal size. In the deprived laminae of the binocular segment, however, cells averaged about two-thirds normal size, and in non-deprived laminae of this segment, neurons were hypertrophied. The hypertrophy was greater for cells in lamina A (40%) than for those in lamina A1 (17%). These data indicate that in monocularly deprived dogs, the monocular segment of the visual system develops normally, but the binocular segment does not. Therefore, we conclude that binocular competition operates in the developing dog's visual system much as it does in the cat's.