HAND PREFERENCES FOR A HAPTIC SEARCHING TASK BY TUFTED CAPUCHINS (CEBUS-APELLA)

We tested the effects of a haptic search task on hand preferences in c apuchins (Cebus apella) and compare this situation to a visual by guid ed reaching task. In the haptic task, 21 monkeys searched for sunflowe r seeds on the top or side surfaces of 12 objects. A left-hand prefere nce emerged at the group level, suggesting a greater involvement of th e right hemisphere. The percentage of preferred hand usage and the dir ection of the preference were influenced by both sex and age of the su bjects: adult males tended to be less lateralized than the other group s of subjects were. Shape had an insignificant effect on the direction of hand preferences or on the percentage of preferred hand use. No la teral bias emerge in the visually guided reaching task, and the percen tage of left-hand usage fell significantly across tasks demonstrating that the haptic demands of the task enhance the use of the left hand a t the group level. We discuss these results with regard to current the ories on manual lateralization in nonhuman primates.