Manual laterality in Callitrichids

Abstract

The current state of evidence for population-level and individual lateral motor asymmetries in nonhuman primates is evaluated in a review of the existing literature. It is accepted that the existence of a population-level left hand bias for simple reaching in prosimians is essentially proven. There appears to be an important association between increased postural demands and increased strength of preferences in prosimians, monkeys and apes. Simple reaching tasks are inadequate to reveal underlying preferences in the manually sophisticated monkeys and apes. More complex unimanual and bimanual tasks tend to elicit indications of a preference for use of the right hand for fine manipulation of objects. Few investigations of lateral preferences in Callitrichids have been conducted so far, and studies linking hand preferences to whole-body turning behaviour have been confined to prosimians, and then only using induced rather than spontaneous measures. There has been no attempt to systematically investigate laterality in manual grooming. Observations of lateral preferences in spontaneous feeding, grooming and turning behaviour were conducted on 21 captive Callitrichid primates. Focal samples were recorded using a laptop computer and specially developed software. Results indicate no population-level laterality for any sampled activity. Most subjects passed objects more often from right to left hands. Preferences were variable in both strength and direction. Strength of turning preference was associated with strength of intermanual transfer and grooming preferences. It is suggested that use of a preferred forelimb for support when turning may be a predictor of lateral preference in these activities. Females made more consecutive left turns than males. This may be due to stronger right forelimb preference for supporting posture.