Behavioral study of the visual cortex of Galago senegalensis.

An ablation study of the visual cortex of Galago senegalensis was undertaken in the hope of finding clues about the evolution of primate visual cortex. Removal of area 17 resulted in a profound sensory loss manifested by, first, the failure to discriminate between simple patterns; second, a deficit in localizing objects; third, a deficiency in tracking moving objects; and fourth, symptoms attributable to a deficiency in depth perception, such as misreaching and inaccurate jumping. Thus, the effects of ablating area 17 are similar in bushbabies and monkeys. In contrast, minimal sensory loss is produced by ablating area 17 in squirrels or tree shrews. This difference between primates and other mammals may depend on differences in the extent of the cortical target of the tecto-pulvinar path; in Galago and perhaps in all primates, more of the extrastriate visual cortex is entirely dependent on area 17. Removal of the ventral temporal cortex resulted in a loss of learned visual discriminations and in retardation in learning new visual discriminations. These symptoms seem related to the inferotemporal syndrome in monkeys.