Hand preference in infant rhesus macaques (Macaca mulatta).

In this research we examined hand preference in infant rhesus macaques (Macaca mulatta). The subjects were 20 Macaca mulatta, each aged between 4 and 11 months. We assessed hand preference using both a unimanual reaching task and a bimanual coordination task. In the unimanual reaching task, we presented subjects with raisins and noted which hand the animals used to retrieve the food. In the bimanual coordination task, we presented the same subjects with plastic tubes filled with raisin paste and noted which hand the animals used to hold the tubes and which hand the animals used to remove the food. We noted a population-level bias toward use of the left hand for both tasks. These results suggest early right hemisphere advantage for reaching and bimanual coordination in Macaca mulatta, although we acknowledge that this issue needs to be examined more directly through neuroimaging procedures such as Positron Emission Tomography (PET) or functional Magnetic Resonance Imaging (fMRI). We speculate that early right hemisphere advantage contributes to differential patterns of hand preference development for unimanual and bimanual action, and that the development of hand preference for bimanual coordination is related to the emergence of hemispheric specialization for processing species-specific vocalizations.