This chapter examines the phenomenon of overimitation: the tendency of young children to copy all of an adult model's actions, even components that are clearly irrelevant for the task at hand. When children observe an adult performing intentional actions on a novel object, they have a strong tendency to encode those actions as causally meaningful—even when there is clear visible evidence to the contrary. This automatic causal encoding process gives children a powerful boost in understanding our species' artifact-rich cultural environment, but it can also lead to vivid errors. In particular, in the rare case of an adult intentionally performing unnecessary actions, children are extremely susceptible to encoding those actions as causally meaningful. It is argued that the resulting distortions in children's causal beliefs are the true cause of overimitation. Though overimitation often appears illogical in the laboratory, in more naturalistic settings it would actually represent a profound learning advantage. Automatic causal encoding affords us a uniquely powerful mechanism for understanding and propagating our knowledge of artifacts, and it may be an important stepping stone in the development of more nuanced causal understanding.

Children are generally masterful imitators, both rational and flexible in their reproduction of others’ actions. After observing an adult operating an unfamiliar object, however, young children will frequently overimitate, reproducing not only the actions that were causally necessary but also those that were clearly superfluous. Why does overimitation occur? We argue that when children observe an adult intentionally acting on a novel object, they may automatically encode all of the adult’s actions as causally meaningful. This process of automatic causal encoding (ACE) would generally guide children to accurate beliefs about even highly opaque objects. In situations where some of an adult’s intentional actions were unnecessary, however, it would also lead to persistent overimitation. Here, we undertake a thorough examination of the ACE hypothesis, reviewing prior evidence and offering three new experiments to further test the theory. We show that children will persist in overimitating even when doing so is costly (underscoring the involuntary nature of the effect), but also that the effect is constrained by intentionality in a manner consistent with its posited learning function. Overimitation may illuminate not only the structure of children’s causal understanding, but also the social learning processes that support our species’ artefact-centric culture.

Mirror neuron’s common coding of action perception and action production raises exciting possibilities for understanding imitation’s neural basis. Thus far, however, theorizing on this score has been hampered by oversimplification of imitation’s complex cognitive reality. This chapter provides a starting point for addressing this problem, synthesizing a broad range of behavioral research into a theoretically unified conception of human imitation. Particular attention is paid to the problem of reconciling selective imitation, in which children rationally omit unnecessary aspects of an adult’s behavior, with overimitation, in which they seem to do exactly the opposite. The apparent contradiction is resolved by refining the notion of selective imitation to its underlying computational basis, and showing that this computational substrate in fact predicts observed patterns of overimitation. Selective imitation and overimitation are thus re-conceptualized as different sides of the same coin—two rational social learning strategies whose superficial opposition conceals a deeper mechanistic and conceptual commonality.

Young children are surprisingly judicious imitators, but there are also times when their reproduction of others' actions appears strikingly illogical. For example, children who observe an adult inefficiently operating a novel object frequently engage in what we termoverimitation, persistently reproducing the adult's unnecessary actions. Although children readily overimitate irrelevant actions that even chimpanzees ignore, this curious effect has previously attracted little interest; it has been assumed that children overimitate not for theoretically significant reasons, but rather as a purely social exercise. In this paper, however, we challenge this view, presenting evidence that overimitation reflects a more fundamental cognitive process. We show that children who observe an adult intentionally manipulating a novel object have a strong tendency to encode all of the adult's actions as causally meaningful, implicitly revising their causal understanding of the object accordingly. This automatic causal encoding process allows children to rapidly calibrate their causal beliefs about even the most opaque physical systems, but it also carries a cost. When some of the adult's purposeful actions are unnecessary—even transparently so—children are highly prone to mis-encoding them as causally significant. The resulting distortions in children's causal beliefs are the true cause of overimitation, a fact that makes the effect remarkably resistant to extinction. Despite countervailing task demands, time pressure, and even direct warnings, children are frequently unable to avoid reproducing the adult's irrelevant actions because they have already incorporated them into their representation of the target object's causal structure.

In the nearly 30 years since Premack and Woodruff famously asked, "Does the chimpanzee have a theory of mind?", the question of exactly how much non-human primates understand about the mental lives of others has had an unusually dramatic history. As little as ten years ago it appeared that the answer would be a simple one, with early investigations of non-human primates' mentalistic abilities yielding a steady stream of negative findings. Indeed, by the mid-1990s even very cautious researchers were ready to flatly assert that Theory of Mind was a uniquely human capacity. Recently, however, an exciting new theoretical perspective on primate social cognition has arisen, and with it the distinct possibility that our evolutionary relatives may understand far more of the social world than we previously believed. In this paper we review new theory and evidence suggesting that non-human primates may indeed represent the mental states of others, at least within the domains for which their distinctive social ecology has prepared them. Having asserted that Premack and Woodruff's original question can be answered with a qualified yes, we then consider the new questions that arise in its place, particularly how and why our own Theory of Mind became more domain-general than that of other primates.

Mirror neurons, located in the premotor cortex of macaque monkeys, are activated both by the performance and the passive observation of particular goal-directed actions. Although this property would seem to make them the ideal neural substrate for imitation, the puzzling fact is that monkeys simply do not imitate. Indeed, imitation appears to be a uniquely human ability. We are thus left with a fascinating question: if not imitation, what are mirror neurons for? Recent advances in the study of non-human primate social cognition suggest a surprising potential answer.

Tomasello et al. provide a new account of cultural uniqueness, one that hinges on a uniquely human motivation to share intentionality with others. We favor an alternative to this motivational account – one that relies on a modular explanation of the primate intention-reading system. We discuss this view in light of recent comparative experiments using competitive intention-reading tasks.