Abstract: This study focuses on the development of spontaneous object manipulation in three infant chimpanzees during their first 2 years of life. The three infants were raised by their biological mothers who lived among a group of chimpanzees. A human tester conducted a series of cognitive tests in a triadic situation where mothers collaborated with the researcher during the testing of the infants. Four tasks were presented, taken from normative studies of cognitive development of Japanese infants: inserting objects into corresponding holes in a box, seriating nesting cups, inserting variously shaped objects into corresponding holes in a template, and stacking up wooden blocks. The mothers had already acquired skills to perform these manipulation tasks. The infants were free to observe the mothers' manipulative behavior from immediately after birth. We focused on object-object combinations that were made spontaneously by the infant chimpanzees, without providing food reinforcement for any specific behavior that the infants performed. The three main findings can be summarized as follows. First, there was precocious appearance of object-object combination in infant chimpanzees: the age of onset (8-11 months) was comparable to that in humans (around 10 months old). Second, object-object combinations in chimpanzees remained at a low frequency between 11 and 16 months, then increased dramatically at the age of approximately 1.5 years. At the same time, the accuracy of these object-object combinations also increased. Third, chimpanzee infants showed inserting behavior frequently and from an early age but they did not exhibit stacking behavior during their first 2 years of life, in clear contrast to human data.

Abstract: Numerous investigators have argued that early ontogenetic immersion in sociocultural environments facilitates cognitive developmental change in human-reared great apes more characteristic of Homo sapiens than of their own species. Such revamping of core, species-typical psychological systems might be manifest, according to this argument, in the emergence of mental representational competencies, a set of social cognitive skills theoretically consigned to humans alone. Human-reared great apes' capacity to engage in “true imitation,” in which both the means and ends of demonstrated actions are reproduced with fairly high rates of fidelity, and laboratory great apes' failure to do so, has frequently been interpreted as reflecting an emergent understanding of intentionality in the former. Although this epigenetic model of the effects of enculturation on social cognitive systems may be well-founded and theoretically justified in the biological literature, alternative models stressing behavioral as opposed to representational change have been largely overlooked. Here I review some of the controversy surrounding enculturation in great apes, and present an alternative nonmentalistic version of the enculturation hypothesis that can also account for enhanced imitative performance on object-oriented problem-solving tasks in human-reared animals.

Abstract: Studies of imitation in animals have become numerous in recent times, but do they contribute to a comparative psychology of social learning? We review this burgeoning field to identify the problems and prospects for such a goal. Difficulties of two main kinds are identified. First, researchers have tackled questions about social learning from at least three very different theoretical perspectives, the “phylogenetic”, “animal model”, and “adaptational”. We examine the conflicts between them and consider the scope for integration. A second difficulty arises in the methodological approaches used in the discipline. In relation to one of these – survey reviews of published studies – we tabulate and compare the contrasting conclusions of nine articles that together review 36 studies. The basis for authors' disagreements, including the matters of perceptual opacity, novelty, sequential structure, and goal representation, are examined. In relation to the other key method, comparative experimentation, we identify 12 studies that have explicitly compared species' imitative ability on similar tasks. We examine the principal problems of comparing like with like in these studies and consider solutions, the most powerful of which we propose to be the use of a systematic range of task designs, rather than any single “gold standard” task.

Abstract: This study explored whether the tendency of chimpanzees and children to use emulation or imitation to solve a tool-using task was a response to the availability of causal information. Young wild-born chimpanzees from an African sanctuary and 3- to 4-year-old children observed a human demonstrator use a tool to retrieve a reward from a puzzle-box. The demonstration involved both causally relevant and irrelevant actions, and the box was presented in each of two conditions: opaque and clear. In the opaque condition, causal information about the effect of the tool inside the box was not available, and hence it was impossible to differentiate between the relevant and irrelevant parts of the demonstration. However, in the clear condition causal information was available, and subjects could potentially determine which actions were necessary. When chimpanzees were presented with the opaque box, they reproduced both the relevant and irrelevant actions, thus imitating the overall structure of the task. When the box was presented in the clear condition they instead ignored the irrelevant actions in favour of a more efficient, emulative technique. These results suggest that emulation is the favoured strategy of chimpanzees when sufficient causal information is available. However, if such information is not available, chimpanzees are prone to employ a more comprehensive copy of an observed action. In contrast to the chimpanzees, children employed imitation to solve the task in both conditions, at the expense of efficiency. We suggest that the difference in performance of chimpanzees and children may be due to a greater susceptibility of children to cultural conventions, perhaps combined with a differential focus on the results, actions and goals of the demonstrator.