Gloria Sabbatini

Inferences about the location of food in capuchin monkeys (Cebus apella) in two sensory modalities.

The authors tested the ability of capuchin monkeys (Cebus apella) to make inferences about hidden food. In Experiment 1, we showed the content of 2 boxes, 1 of which was baited (visual condition, VC) or we shook both boxes producing noise from the baited box (auditory condition, AC). Seven subjects (out of 8) were above chance in the VC, whereas only 1 was above chance in AC. During treatment, by manipulating empty and filled objects subjects experienced the relation between noise and content. When tested again, 7 capuchins were above chance in the VC and 3 in AC. In Experiment 2, we gave visual or auditory information only about the empty box and, consequently, successful choice implied inferential reasoning. All subjects (out of 4) were above chance in the VC, and 2 in the AC. Control tests ruled out the possibility that success resulted from simply avoiding the shaken noiseless box, or from the use of arbitrary auditory information. Similar to apes (Call, 2004), capuchins were capable of inferential reasoning.

Food transfers in capuchin monkeys: an experiment on partner choice

Although most primates live in groups, experiments on reciprocity usually test individuals in dyads. This could hide the processes emerging in richer social settings, reducing the ecological validity of the results. We run an experiment on reciprocal food transfers testing capuchin monkeys (Cebus apella) in triads, so that subjects could choose to allow access to their food to either of their two partners. We tested the hypothesis that partner choice was related to a comparison of long-term social bonds with the two partners, more than to a comparison of recent food transfer events from the two partners. The results confirmed this hypothesis, thus supporting the notion that reciprocal partner preferences are based on long-term accounts of benefits that have been exchanged.

Understanding the functional properties of tools: chimpanzees (Pan troglodytes) and capuchin monkeys (Cebus apella) attend to tool features differently

We examined whether eight capuchins and eight chimpanzees were able to retrieve a reward placed inside a tube, of varying length, by selecting the correct stick from different sets of three sticks differing in length (functional feature) and handle (non-functional feature). Moreover, to investigate whether seeing the stick inside the tube (visual feedback) improves performance, half of the subjects were tested with a transparent apparatus and the other half with an opaque apparatus. Phase 1 included (a) Training 1 in which each stick had a different handle and (b) Transfer 1 in which the handles were switched among sticks, so that the functional tool had the same length but a different handle than before. The seven chimpanzees and one capuchin that passed Transfer 1 received Transfer 2. The other subjects received (a) Training 2, which used the same sticks from Phase 1 with handles switched in every trial, and (b) Transfer 2 in which the tube was longer, all sticks had the same new handle, and the formerly longest tool became intermediate in length. Eight chimpanzees and three capuchins passed Transfer 2. Results showed that (1) chimpanzees applied relational structures in tool using tasks more quickly than capuchins and (2) capuchins required more varied experience to attend to the functional feature of the tool. Interestingly, visual feedback did not improve performance in either species.

Tool choice on the basis of rigidity in capuchin monkeys

Wild capuchin monkeys select stone tools to crack open nuts on the basis of their weight and friability, two non-visual functional properties. Here, we investigated whether they would select new stick-like tools on the basis of their rigidity. In Experiment 1, subjects faced an out-of-reach reward and a choice of three unfamiliar tools differing in color, diameter, material, and rigidity. In order to retrieve the reward, capuchins needed to select the rigid tool exemplar. Capuchins gathered information regarding tools’ pliability either by (1) manipulating the tools themselves (manipulation condition), (2) observing a human demonstrator repeatedly bending the tools (observation condition), or (3) seeing the tools placed on a platform without any manipulation taking place (visual static condition). Subjects selected the rigid tool above chance levels in both the manipulation and observation conditions, but not in the visual static condition. In Experiment 2, subjects needed to select and use a flexible tool to access a liquid reward (as opposed to the rigid tool, as in previous experiment). Again, capuchins selected above chance levels the appropriate tool (i.e., flexible), thus demonstrating a good appreciation of the relation between the tool properties and the task requirements.

A mechatronic platform for behavioral analysis on nonhuman primates

In this work we present a new mechatronic platform for measuring behavior of nonhuman primates, allowing high reprogrammability and providing several possibilities of interactions. The platform is the result of a multidisciplinary design process, which has involved bio-engineers, developmental neuroscientists, primatologists, and roboticians to identify its main requirements and specifications. Although such a platform has been designed for the behavioral analysis of capuchin monkeys (Cebus apella), it can be used for behavioral studies on other nonhuman primates and children. First, a state-of-the-art principal approach used in nonhuman primate behavioral studies is reported. Second, the main advantages of the mechatronic approach are presented. In this section, the platform is described in all its parts and the possibility to use it for studies on learning mechanism based on intrinsic motivation discussed. Third, a pilot study on capuchin monkeys is provided and preliminary data are presented and discussed.

Abstract knowledge in the broken-string problem : evidence from nonhuman primates and pre-schoolers

There is still large controversy about whether abstract knowledge of physical problems is uniquely human. We presented 9 capuchin monkeys, 6 bonobos, 6 chimpanzees and 48 children with two versions of a broken-string problem. In the standard condition, participants had to choose between an intact and a broken string as means to a reward. In the critical condition, the functional parts of the strings were covered up and replaced by perceptually similar, but non-functional cues. Apes, monkeys and young children performed significantly better in the standard condition in which the cues played a functional role, indicating knowledge of the functional properties involved. Moreover, a control experiment with chimpanzees and young children ruled out that this difference in performance could be accounted for by differences of perceptual feedback in the two conditions. We suggest that, similar to humans, nonhuman primates partly rely on abstract concepts in physical problem-solving.

Exploration and learning in capuchin monkeys (Sapajus spp.): the role of action-outcome contingencies.

Animals have a strong propensity to explore the environment. Spontaneous exploration has a great biological significance since it allows animals to discover and learn the relation between specific behaviours and their consequences. The role of the contingency between action and outcome for learning has been mainly investigated in instrumental learning settings and much less in free exploration contexts. We tested 16 capuchin monkeys (Sapajus spp.) with a mechatronic platform that allowed complex modules to be manipulated and to produce different outcomes. Experimental subjects could manipulate the modules and discover the contingencies between their own specific actions and the outcomes produced (i.e., the opening and lighting of a box). By contrast, Control subjects could operate on the modules, but the outcomes experienced were those performed by their paired Experimental subjects (“yoked-control” paradigm). In the exploration phase, in which no food reward was present, Experimental subjects spent more time on the board and manipulated the modules more than Yoked subjects. Experimental subjects outperformed Yoked subjects in the following test phase, where success required recalling the effective action so to open the box, now baited with food. These findings demonstrate that the opportunity to experience action–outcome contingencies in the absence of extrinsic rewards promotes capuchins’ exploration and facilitates learning processes. Thus, this intrinsically motivated learning represents a powerful mechanism allowing the acquisition of skills and cognitive competence that the individual can later exploit for adaptive purposes.

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.

The “Mechatronic Board”: A Tool to Study Intrinsic Motivations in Humans, Monkeys, and Humanoid Robots

In this chapter the design and fabrication of a new mechatronic platform (called “mechatronic board”) for behavioural analysis of children, non-human primates, and robots are presented and discussed. The platform is the result of a multidisciplinary design approach which merges indications coming from neuroscientists, psychologists, primatologists, roboticists, and bioengineers, with the main goal of studying learning mechanisms driven by intrinsic motivations and curiosity. This chapter firstly introduces the main requirements of the platform, coming from the different needs of the experiments involving the different types of participants. Then, it provides a detailed analysis of the main features of the mechatronic board, focusing on its key aspects which allow the study of intrinsically motivated learning in children and non-human primates. Finally, it shows some preliminary results on curiosity-driven learning coming from pilot experiments involving children, capuchin monkeys, and a computational model of the behaviour of these organisms tested with a humanoid robot (the iCub robot). These experiments investigate the capacity of children, capuchin monkeys, and a computational model implemented on the iCub robot to learn action-outcome contingencies on the basis of intrinsic motivations.

Motor planning in different grasping tasks by capuchin monkeys (Sapajus spp.)

Studies on motor planning and action selection in object use reveal that what we choose to do in the present moment depends on our next planned action. In particular, many studies have shown that adult humans initially adopt uncomfortable hand postures to accommodate later task demands (i.e., the end-state comfort effect). Recent studies on action planning in different non-human primates species have provided contrasting results. Here, we tested whether capuchin monkeys (Sapajus spp.), natural tool users, would show planning abilities in two tasks with varying complexity: (i) an object-retrieval task involving self-directed actions (Experiment 1) and (ii) a tool-using task involving actions directed toward an external target (Experiment 2). In Experiment 1, six of 10 monkeys preferentially used a radial grip (i.e., with the thumb-side oriented towards the baited end) to grasp a horizontal dowel with either the left- or right-end baited and bring it to their mouth. In Experiment 2, all six tested capuchins preferentially used a radial grip (i.e., with the thumb-side oriented towards the center of the dowel) to grasp a dowel that was positioned horizontally at different orientations and to dislodge an out-of-reach food reward. Thus, we found that the capuchins showed second-order planning abilities in both tasks, but performance differences emerged in relation to hand preference and learning across sessions. Our findings support the idea that second-order motor planning occurred in an early stage of the primate lineage. Factors affecting the ability of nonhuman primates to estimate motor costs in action selection are discussed.