ABSTRACT
The existence of two distinct visual pathways was first discovered in studies of primates some forty years ago. They were originally named the "what" and "where" pathways, assuming that the former was involved in identifying what was seen, and the latter in where it was located. One of the primate experiments that revealed the distinctive roles of the two pathways involved two tests on rhesus monkeys. One group had the identity pathway ablated, and one group had the control pathway ablated. In many tests of the visual pathways, subjects are fitted with special glasses that are turned opaque under the control of the experimenter. The control pathway terminates in the parietal lobe, and damage to this area leads to a condition called optic ataxia. It was experiments like this that led M. A. Goodale and A. D. Milner to look for evidence of two visual pathways with distinctive roles in humans.
