Hand preferences in 26 capuchin monkeys (Cebus apelld) were examined in 2 reaching-forfood tasks under 2 postural conditions. In the 1st task (unimanual), monkeys were required to reach for food from both a quadrupedal and an upright posture. A right-hand bias was found for the upright but not for the quadrupedal condition. In the 2nd task (coordinated bimanual), monkeys were required to extract the food from a hanging Plexiglas tube from both a crouched and an upright posture. A right-hand bias was found for both conditions. A significant increase in right-hand use was noted from the unimanual, quadrupedal, reaching task to the coordinated-bimanual task, with females exhibiting a greater right-hand preference than males. In addition, a significant effect of task complexity on strength in laterality was found. Results are discussed in the context of recent theories on primate laterality.

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Consiglio Nazionale delle RicercheCapuchin monkeys' (Cebus apella) relative accuracy in the processing of the global shape or the local features of hierarchical visual stimuli was assessed. Three experiments are presented featuring manipulations of the arrangement and the density of the local elements of the stimuli. The results showed a clear advantage for local level processing in this species, which is robust under manipulations of the density of the local elements of the stimuli. By contrast, the density of the component elements linearly affected accuracy in global processing. These findings, which support those from other studies in which a local superiority emerged in animals, challenge the generality of early claims concerning the adaptive value of global advantage in the processing of hierarchical visual patterns.On the basis of his findings concerning the perceptual processing of visual stimuli, Navon (1977, 1981) argued that the human perceptual system processes the global features of a visual scene before proceeding to a more fine-grained analysis of local details. This hypothesis, termed the global dominance or global precedence hypothesis (Navon, 1977), was supported by the results of a series of experiments in which adult subjects were presented with hierarchically structured stimuli consisting of large letters made up of small letters. Navon observed that the accuracy and latency for visual detection response were better and shorter, respectively, when participants had to attend to global aspects of compound stimuli than when they were required to attend to their local features. Furthermore, in conditions in which attention had to be directed to local features, but not in conditions in which attention had to be directed toward the global form of the stimuli, the identity of the global level letter did affect subjects' discriminative responses. Global characters that conflicted with the local ones (e.g., a large S made of small Hs) slowed down the perception of local level stimuli, whereas the identity of the local elements did not affect the recognition of global level hierarchical patterns. Navon interpreted this global-to-local interference as evidence for his global precedence hypothesis.

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.

I investigated the development of spontaneous classificatory behavior in 5 chimpanzees (Pan troglodytes) tested at different ages and analyzed subjects' spontaneous constructive interactions with sets of logically structured objects. The results show that chimpanzees possess a natural capacity to react to similarities and differences among test stimuli and construct classes. The general progression of their classificatory development is very similar to that reported for human infants from 6 to 24 months. In both species, classification progresses from constructing single classes by different properties of objects to constructing single classes by similar or identical properties of objects. In addition, like humans, older chimpanzees spontaneously coordinate relations of similarities between sets and construct 2 class-consistent groupings. Chimpanzees' results are compared with those from a similar study with capuchins and macaques.