Versatile grasping ability in power-grip actions by tufted capuchin monkeys (Sapajus spp.).

OBJECTIVES: Capuchin monkeys are well known to have a high degree of manual dexterity. In this study, we assessed the variability of capuchin 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 that do not necessarily involve individually controlled finger movements. Planning abilities in executing actions were also evaluated. METHODS: Twenty tufted capuchins (Sapajus spp.) were tested in a task requiring individuals to grasp a dowel inserted into a vertical tube. We examined their grasping techniques, focusing on the following aspects: (i) the different hand postures made during grasping, (ii) the frequency of thumb use in opposition to the other fingers, (iii) the asymmetric use of the hands, and (iv) the configuration of the grasping action for the purpose of comfortably bringing the food to the mouth. RESULTS: Eight power-grip variants were identified, with individual capuchins performing an average of more than five different grips. The use of the thumb in opposition to the other areas of the hand, as reported in studies of precision grips, also appears to be a common feature in power grips. No evidence of group-level manual asymmetries was found. Adult capuchins were better than immature individuals in planning grasping actions in relation to following task demands. DISCUSSION: Overall, these findings clarify the extent to which manual dexterity and cognitive abilities can be expressed in the grasping tasks of highly manually skilled primate species.

Grasping behavior in tufted capuchin monkeys (Cebus apella): grip types and manual laterality for picking up a small food item.

This study investigates prehension in 20 tufted capuchins (Cebus apella) in a reaching task requiring individuals to grasp a small food item fixed to a tray. The aim was twofold: 1) to describe capuchins' grasping techniques in detail, focusing on digit movements and on different areas of contact between the grasping fingers; and 2) to assess the relationship between grip types and manual laterality in this species. Capuchins picked up small food items using a wide variety of grips. In particular, 16 precision grip variants and 4 power grip variants were identified. The most frequently used precision grip involved the distal lateral areas of the thumb and the index finger, while the most preferred kind of power grip involved the thumb and the palm, with the thumb being enclosed by the other fingers. Immature capuchins picked up small food items using power grips more often than precision grips, while adult individuals exhibited no significant preference for either grip type. The analysis performed on the time capuchins took to grasp the food and withdraw it from the tray hole revealed that 1) precision grips were as efficient as power grips; 2) for precision grips, the left hand was faster than the right hand; and 3) for power grips, both hands were equally quick. Hand preference analysis, based on the frequency for the use of either hand for grasping actions, revealed no significant hand bias at group level. Likewise, there was no significant relationship between grip type and hand preference.