Hand preferences for a haptic searching task by tufted capuchins (Cebus apella)

Abstract

We tested the effects of a haptic search task on hand preferences in capuchins(Cebus apella) and compare this situation to a visual by guided reaching task. In the haptic task, 21 monkeys searched for sunflower seeds on the top or side surfaces of 12 objects. A left-hand preference emerged at the group level, suggesting a greater involvement of the right hemisphere. The percentage of preferred hand usage and the direction of the preference were influenced by both sex and age of the subjects: adult males tended to be less lateralized than the other groups of subjects were. Shape had an insignificant effect on the direction of hand preferences or on the percentage of preferred hand use. No lateral bias emerge in the visually guided reaching task, and the percentage of left-hand usage fell significantly across tasks, demonstrating that the haptic demands of the task enhance the use of the left hand at the group level. We discuss these results with regard to current theories on manual lateralization in nonhuman primates.