Stereoblind monkeys have few binocular neurons.

Infant monkeys wore prisms before their eyes, lost binocular neurons from their visual cortex, and were stereoblind to dynamic random dot stereograms. Three years later, the authors recorded from 880 neurons of the V1 and V2 visual cortex and found only 22% binocular neurons as compared with 81% for normal monkeys. These results demonstrate, for the first time in the same subjects, the strong association between cortical binocular neurons and primate stereopsis; show that congenital binocular neurons, once lost, do not recover even with extensive binocular visual experience; and stress the vulnerability of the primate binocular system to abnormal early visual experiences.