Manual laterality in spider monkeys (Ateles geoffroyi) solving visually and tactually guided food-reaching tasks.

The purpose of this study was to assess the occurrence of manual laterality in Ateles geoffroyi and in particular to test the influence of visual and tactual control on preferential hand use. Thirteen spider monkeys were presented with three different food-reaching tasks and assessed for hand preferences with a minimum of 100 reaches per animal. In all three tasks a significant lateral bias towards use of the left hand at the group level was found. Performance in visually and tactually guided reaching tasks did not differ with regard to direction or degree of manual laterality. Males and females showed no significant differences in performance with the exception that males used their mouths to retrieve food when the task permitted, significantly more often than females. The results suggest a possible right-hemisphere specialization in the spider monkey for both visually and tactually guided reaching.