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Byrnl, R. W., & Tomasello, M. (1995). Do rats ape? Anim. Behav., 50(5), 1417–1420.
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Hare, B., Call, J., & Tomasello, M. (2001). Do chimpanzees know what conspecifics know? Anim. Behav., 61(1), 139–151.
Abstract: We conducted three experiments on social problem solving by chimpanzees, Pan troglodytes. In each experiment a subordinate and a dominant individual competed for food, which was placed in various ways on the subordinate's side of two opaque barriers. In some conditions dominants had not seen the food hidden, or food they had seen hidden was moved elsewhere when they were not watching (whereas in control conditions they saw the food being hidden or moved). At the same time, subordinates always saw the entire baiting procedure and could monitor the visual access of their dominant competitor as well. If subordinates were sensitive to what dominants did or did not see during baiting, they should have preferentially approached and retrieved the food that dominants had not seen hidden or moved. This is what they did in experiment 1 when dominants were either uninformed or misinformed about the food's location. In experiment 2 subordinates recognized, and adjusted their behaviour accordingly, when the dominant individual who witnessed the hiding was replaced with another dominant individual who had not witnessed it, thus demonstrating their ability to keep track of precisely who has witnessed what. In experiment 3 subordinates did not choose consistently between two pieces of hidden food, one of which dominants had seen hidden and one of which they had not seen hidden. However, their failure in this experiment was likely to be due to the changed nature of the competition under these circumstances and not to a failure of social-cognitive skills. These findings suggest that at least in some situations (i.e. competition with conspecifics) chimpanzees know what conspecifics have and have not seen (do and do not know), and that they use this information to devise effective social-cognitive strategies. Copyright 2001 The Association for the Study of Animal Behaviour.
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Tomasello, M., Hare, B., & Agnetta, B. (1999). Chimpanzees, Pan troglodytes, follow gaze direction geometrically. Anim. Behav., 58(4), 769–777.
Abstract: Two experiments on chimpanzee gaze following are reported. In the first, chimpanzee subjects watched as a human experimenter looked around various types of barriers. The subjects looked around each of the barriers more when the human had done so than in a control condition (in which the human looked in another direction). In the second experiment, chimpanzees watched as a human looked towards the back of their cage. As they turned to follow the human's gaze a distractor object was presented. The chimpanzees looked at the distractor while still following the human's gaze to the back of the cage. These two experiments effectively disconfirm the low-level model of chimpanzee gaze following in which it is claimed that upon seeing another animate being's gaze direction chimpanzees simply turn in that direction and look around for something interesting. Rather, they support the hypothesis that chimpanzees follow the gaze direction of other animate beings geometrically to specific locations, in much the same way as human infants. The degree to which chimpanzees have a mentalistic interpretation of the gaze and/or visual experience of others is still an open question.
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Hare, B., Addessi, E., Call, J., Tomasello, M., & Visalberghi, E. (2003). Do capuchin monkeys, Cebus apella, know what conspecifics do and do not see? Anim. Behav., 65(1), 131–142.
Abstract: Capuchin monkeys were tested in five experiments in which two individuals competed over food. When given a choice between retrieving a piece of food that was visible or hidden from the dominant, subordinate animals preferred to retrieve hidden food. This preference is consistent with the hypotheses that either (1) the subordinate knew what the dominant could and could not see or (2) the subordinate was monitoring the behaviour of the dominant and avoiding the piece of food that it approached. To test between these alternatives, we released subordinates with a slight head start forcing them to make their choice (between a piece of food hidden or visible to the dominant) before the dominant entered the area. Unlike chimpanzees, Pan troglodytes, subordinates that were given a head start did not preferentially approach hidden pieces of food first. Therefore, our experiments provide little support for the hypothesis that capuchin monkeys are sensitive to what another individual does or does not see. We compare our results with those obtained with chimpanzees in the same paradigm and discuss the evolution of primate social cognition. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.
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Hare, B., Call, J., Agnetta, B., & Tomasello, M. (2000). Chimpanzees know what conspecifics do and do not see. Anim. Behav., 59(4), 771–785.
Abstract: We report a series of experiments on social problem solving in chimpanzees, Pan troglodytes. In each experiment a subordinate and a dominant individual were put into competition over two pieces of food. In all experiments dominants obtained virtually all of the foods to which they had good visual and physical access. However, subordinates were successful quite often in three situations in which they had better visual access to the food than the dominant, for example, when the food was positioned so that only the subordinate (and not the dominant) could see it. In some cases, the subordinate might have been monitoring the behaviour of the dominant directly and simply avoided the food that the dominant was moving towards (which just happened to be the one it could see). In other cases, however, we ruled out this possibility by giving subordinates a small headstart and forcing them to make their choice (to go to the food that both competitors could see, or the food that only they could see) before the dominant was released into the area. Together with other recent studies, the present investigation suggests that chimpanzees know what conspecifics can and cannot see, and, furthermore, that they use this knowledge to devise effective social-cognitive strategies in naturally occurring food competition situations.
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Hare, B., & Tomasello, M. (2004). Chimpanzees are more skilful in competitive than in cooperative cognitive tasks. Anim. Behav., 68(3), 571–581.
Abstract: In a series of four experiments, chimpanzees, Pan troglodytes, were given two cognitive tasks, an object choice task and a discrimination task (based on location), each in the context of either cooperation or competition. In both tasks chimpanzees performed more skilfully when competing than when cooperating, with some evidence that competition with conspecifics was especially facilitatory in the discrimination location task. This is the first study to demonstrate a facilitative cognitive effect for competition in a single experimental paradigm. We suggest that chimpanzee cognitive evolution is best understood in its socioecological context.
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Hare, B., & Tomasello, M. (2005). Human-like social skills in dogs? Trends. Cognit. Sci., 9(9), 439–444.
Abstract: Domestic dogs are unusually skilled at reading human social and communicative behavior--even more so than our nearest primate relatives. For example, they use human social and communicative behavior (e.g. a pointing gesture) to find hidden food, and they know what the human can and cannot see in various situations. Recent comparisons between canid species suggest that these unusual social skills have a heritable component and initially evolved during domestication as a result of selection on systems mediating fear and aggression towards humans. Differences in chimpanzee and human temperament suggest that a similar process may have been an important catalyst leading to the evolution of unusual social skills in our own species. The study of convergent evolution provides an exciting opportunity to gain further insights into the evolutionary processes leading to human-like forms of cooperation and communication.
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Kaminski, J., Riedel, J., Call, J., & Tomasello, M. (2005). Domestic goats, Capra hircus, follow gaze direction and use social cues in an object choice task. Anim. Behav., 69(1), 11–18.
Abstract: Gaze following is a basic social cognitive skill with many potential benefits for animals that live in social groups. At least five primate species are known to follow the gaze of conspecifics, but there have been no studies on gaze following in other mammals. We investigated whether domestic goats can use the gaze direction of a conspecific as a cue to find food. They were able to do this, at a level comparable to that of primates. In a second experiment, we tested goats' ability to use gaze and other communicative cues given by a human in a so-called object choice situation. An experimenter hid food out of sight of the subject under one of two cups. After baiting the cup the experimenter indicated the location of the food to the subject by using different cues. The goats used communicative cues (touching and pointing) but not gaze by itself. Since domestic dogs are very skilled in this task, whereas wolves are not, one hypothesis is that the use of communicative cues in the object choice task is a side-effect of domestication.
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Melis, A. P., Hare, B., & Tomasello, M. (2006). Engineering cooperation in chimpanzees: tolerance constraints on cooperation. Anim. Behav., 72(2), 275–286.
Abstract: The cooperative abilities of captive chimpanzees, Pan troglodytes, in experiments do not match the sophistication that might be predicted based on their naturally occurring cooperative behaviours. This discrepancy might partly be because in previous experiments potential chimpanzee cooperators were partnered without regard to their social relationship. We investigated the ability of chimpanzee dyads to solve a physical task cooperatively in relation to their interindividual tolerance levels. Pairs that were most capable of sharing food outside the test were also able to cooperate spontaneously (by simultaneously pulling two ropes) to obtain food. In contrast, pairs that were less inclined to share food outside of the test were unlikely to cooperate. Furthermore, previously successful subjects stopped cooperating when paired with a less tolerant partner, even when the food rewards were presented in a dispersed and divisible form to reduce competition between subjects. These results show that although chimpanzees are capable of spontaneous cooperation in a novel instrumental task, tolerance acts as a constraint on their ability to solve such cooperative problems. This finding highlights the importance of controlling such social constraints in future experiments on chimpanzee cooperation, and suggests that the evolution of human-like cooperative skills might have been preceded by the evolution of a more egalitarian social system and a more human-like temperament.
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Herrmann, E., Melis, A. P., & Tomasello, M. (2006). Apes' use of iconic cues in the object-choice task. Anim. Cogn., 9(2), 118–130.
Abstract: In previous studies great apes have shown little ability to locate hidden food using a physical marker placed by a human directly on the target location. In this study, we hypothesized that the perceptual similarity between an iconic cue and the hidden reward (baited container) would help apes to infer the location of the food. In the first two experiments, we found that if an iconic cue is given in addition to a spatial/indexical cue – e.g., picture or replica of a banana placed on the target location – apes (chimpanzees, bonobos, orangutans, gorillas) as a group performed above chance. However, we also found in two further experiments that when iconic cues were given on their own without spatial/indexical information (iconic cue held up by human with no diagnostic spatial/indexical information), the apes were back to chance performance. Our overall conclusion is that although iconic information helps apes in the process of searching hidden food, the poor performance found in the last two experiments is due to apes' lack of understanding of the informative (cooperative) communicative intention of the experimenter.
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