Discrimination of monkey faces by split-brain monkeys

Eighteen split-brain rhesus monkeys were tested with each hemisphere for the ability to learn to discriminate photographs of the faces of other monkeys. Seven subjects also ran tests of generalization to new photographs of the discriminated monkeys; these tests confirmed that facial features pertaining to individual monkeys were learned. Equal numbers of male and female monkeys and nearly equal numbers of right and left handed monkeys were tested. Over all the monkeys there was no significant advantage in learning with either the left or right hemisphere or with the hemisphere contralateral or ipsilateral to the preferred hand. The group of 9 female monkeys, however, did show a significant advantage in learning with the left hemisphere. Furthermore, there was a tendency for monkeys older at the time of surgery to show greater hemispheric specialization.