Effects of early unilateral blur on the macaque's visual system. III. Physiological observations.

We studied the properties of visual cortical and lateral geniculate neurons in 5 macaque monkeys raised with the vision of one eye blurred by daily instillation of atropine. This rearing reduced the degree of binocular interaction in striate cortical neurons and caused a modest shift in eye dominance away from the atropine-treated eye. It also led to a difference in the spatial properties of neurons driven by the 2 eyes: neurons driven by the treated eye tended to have lower optimal spatial frequencies, poorer spatial resolution, and lower contrast sensitivity than neurons driven by the untreated eye. Some of the few binocularly driven neurons had receptive fields with sharply different spatial properties in the 2 eyes, with the treated eye's receptive field always having poorer spatial resolution. In striate cortex, the effects on neuronal spatial properties were less marked in layer 4 than in more superficial or deeper layers; there was no difference in the spatial properties of lateral geniculate neurons driven by the 2 eyes. A small sample of extrastriate cortical neurons from a single animal showed effects similar to those seen in striate cortex. The striate cortical changes varied consistently from animal to animal: The less affected animals had no discernible eye dominance shift and relatively small differences in spatial properties between the eyes; the more affected animals had substantial eye dominance shifts and larger interocular spatial differences. These variations were also reflected in, and consistent with, behavioral and anatomical measurements performed in the same monkeys.