Effects of Facial Identity, Facial Expression, and Subject's Sex on Laterality in Monkeys

Abstract

Previously we showed that rhesus monkeys processed discriminations of monkey faces significantly better with the right hemisphere of the brain than with the left. The overall effects of the type of discrimination, i.e. facial identity or expression, and the sex of the subject on laterality are examined here for seven phases of this series of experiments. Both types of discrimination produced a right hemispheric advantage, with slightly greater laterality for expression, but generally the laterality did not differ significantly for the two types. Female monkeys demonstrated more consistent and significant right hemispheric laterality than did males. Furthermore, female monkeys tended to be more lateralised for discriminations of expression, whereas males were about equally lateralised for both types. Thus, in these experiments the overall right hemispheric advantage for facial discriminations in monkeys reflects the contribution of the female subjects, especially when discriminating expression, more than that of the males.