Grasping behavior and object manipulation rely on both motor and cognitive skills. In fact, motor planning requires cognitive ability in selecting actions and acknowledging errors as well as motor ability in executing actions. Among non-human primates, capuchin monkeys are well-known to have a high degree of manual dexterity. In this study we assessed the variability of capuchins' grasping actions involving power grips, i.e. manual actions in which the object is grasped between the palm and one or several parts of the fingers and do not necessarily involve independent movements of the fingers. To this purpose, 20 tufted capuchin monkeys (Sapajus spp.) were tested in a task requiring individuals to grasp a stick inserted into a vertical tube. Each individual used an average of more than five different grip types, revealing a flexible use of the hand and a preference for the use of the thumb in opposition to the other fingers. Moreover, action planning abilities varied in relation to age. The results were discussed in light of how the study on object manipulation contributes to our knowledge about the connection between cognition and action.
