Handedness and manual specialization in the baboon.

Manual preferences of six baboons were tested with three kinds of experimental tasks: (1) a simple reaching on a board or in a hole; (2) a box opening; (3) two visuo-spatial tasks requiring precise alignments of apertures. The distribution of right and left hand preferences was found to be symmetrical for the simple reachings (3 right- and 3 left-handers) and was consistent with the preferences in the box opening task. However, manual tasks with strong visuo-spatial components gave a unimodal distribution with a left hand preference for the group for aligning and adjusting the apertures. These results suggest the coexistence within an individual of two types of preferences according to the distinction between handedness and manual specialization.