Imitation is generally acknowledged as a key mechanism of social learning, foundational to the emergence of human culture. By enabling quick and high-fidelity copying of others’ actions, imitation mediates the crossgenerational transfer of knowledge and skills (e.g. Nielsen, 2009). Besides this ‘learning’ (or ‘cognitive’) function, imitation accomplishes also important social-communicative functions, by facilitating social interaction and promoting prosociality (e.g. Duffy & Chartrand 2015; Eckerman, Davis, & Didow, 1989; Užgiris, Benson et al., 1989). The social function of imitation is understudied in the field of comparative psychology, or even claimed to be absent in nonhuman primates. This claim, however, is grounded on how nonhuman apes (henceforth ‘apes’) perform in imitation learning experiments compared to human children. More specifically, chimpanzees exhibit lower levels of joint attention and gaze at the experimenter’s face (Carpenter & Tomasello, 1995). Moreover, children - but not chimpanzees - exhibit ‘over-imitation’, i.e. they show a propensity for faithfully copying demonstrated actions, even when these actions are irrelevant for achieving a demonstrated outcome. Such differences, it has been argued, derive from the fact that, in imitation contexts, children are motivated by a need to belong, to engage socially and to promote shared experiences (Carpenter & Call 2009; Nielsen 2009). In turn, these differences in social motivation are taken to account for the profound differences that exist between human and nonhuman primate cultures (Over & Carpenter 2012).
Based on evidence from social, developmental and comparative psychology, we have recently proposed a broader definition of the social-communicative function of imitation (Persson, Sauciuc, & Madsen, 2017), that encompasses reactive and non-intentional phenomena (e.g. nonconscious mimicry, imitation-induced prosociality), as well as proactive and arguably intentional phenomena, such as social conformism or the communicative imitation documented in preverbal toddlers (e.g. Eckerman, Davis, & Didow, 1989; Eckerman & Stein, 1990). All these phenomena have been documented in nonhuman primates: nonconscious mimicry in the form of postural congruence (Jazrawi, 2000), facial mimicry (Scopa & Palagi, 2016), interactional synchrony (Yu and Tomonaga, 2016) and contagious yawning (Madsen, Persson, et al., 2013), imitation-induced prosociality expressed by increased levels of attention, proximity and object exchange after exposure to being imitated (e.g. Paukner, Suomi et al., 2009), social conformism in the form of a preference for a group-adopted procedure even when it went against a prefered or more efficient one (Hopper, Schapiro, et al., 2011), and communicative imitation in the form of familiar-action imitation used to engage or maintain interaction (Persson, Sauciuc, & Madsen, 2017).
In this presentation, we address the presence of shared intentionality in imitative contexts with evidence from four experimental studies that our team has conducted with 6-month old infants (Sauciuc, Madsen, et al., in prep), as well as with enculturated (Sauciuc, Persson, & Madsen, in prep) and non-enculturated (Madsen, Sauciuc, & Persson, in prep a, b) chimpanzees of various ages (infants, juveniles, adults). Common to all these studies is that the participants have been exposed to an imitation condition in which the experimenter imitated all their actions, as well as to a number of control conditions that varied in agreement with the specific aims of each study. In Sauciuc, Madsen et al. (in prep), to establish if 6-month old infants discriminate being imitated from contingent responding, and to examine likely mechanisms that mediate this process, infants interacted with an experimenter who (i) imitated all infant’s action ipsilaterally; (ii) imitated all infant’s actions contralaterally; (iii) imitated with a still-face, i.e. imitated bodily but not facial actions; or (iv) responded with the infant’s actions contingently but with different actions. In Madsen, Sauciuc, & Persson (in prep a), to track the ontogenetic course of imitation recognition in chimpanzees, we replicated Haun and Call’s (2008) study on imitation recognition in adult apes and exposed infant and juvenile chimpanzees to four types of interaction in which the experimenter either (i) imitated all chimpanzee’s actions; (ii) responded to the chimpanzee’s actions with temporally contingent but different actions; (iii) produced actions that were not related to the chimpanzee’s actions; (iv) sat still. In Sauciuc, Persson, & Madsen (in prep) four additional control conditions were administered in order to ascertain that behavioural indicators of shared intentionality (e.g. imitation games, laughter) could not be attributed to alternative factors known to increase playfulness in chimpanzees, including non-play species-specific behaviours, species-specific play forms (chase) or facial expressions that accompany play. Finally, in Madsen, Sauciuc, & Persson (in prep b), chimpanzees were exposed to bouts of (i) imitation, (ii) non-imitative play and (iii) no action in order to investigate the effects of imitation and non-imitative play on subsequent intentional imitation of non-instrumental actions and nonconscious mimicry (such as contagious yawning).
To examine the presence of shared intentionality in the studied populations, we focused on the presence of testing behaviours and imitation games, as well as on the presence of smiling and laughter during such responses. ‘Testing behaviours’ are generally acknowledged as an indication of explicit imitation recognition, i.e. that the imitated individual is aware of the imitator’s intention to copy his/her behaviours (Whiten & Suddendorf, 2001). They may take the form of ‘behavioural repetitions’ (the imitated individual repeatedly reproduces a previously imitated action), ‘testing sequences’ (the imitated individual produces rapidly a series of different actions) or ‘testing poses’ (the imitated individual suddenly freeze in a posture). Such ‘testing behaviours’ are generally regarded as a mean by which the imitated individual actively tests the contingent correspondence between own actions and those of the imitator. The presence of testing behaviours is thus considered to be an indication that the imitated individual is aware of this action correspondence, as well as of the impact that his/her actions has on the behaviour of the imitator (e.g. Bates & Byrne, 2010;). Testing behaviours have been documented in human infants as early as 9-months of age (Agnetta & Rochat, 2004) and in apes (e.g. Haun & Call, 2008), but not in monkeys. Unlike human infants, however, apes do not seem to exhibit shared intentionality in such imitative contexts, i.e. they do not show signs of enjoyment and playfulness (laughter, imitation games) when being systematically imitated (Nielsen, 2009). Contrary to this view, our studies bring evidence that both enculturated and non-enculturated chimpanzees show enjoyment and playfulness when being imitated. Indeed, laughter and imitation games were present in both young and adult chimpanzees, in both enculturated and non-enculturated populations. We have also found that human infants produced testing behaviours as early as 6 months of age, and that they engaged in imitation games accompanied by smiling regardless of whether the experimenter imitated them ipsilaterally, contralaterally or with a still-face. In all the studied populations, testing behaviours were primarily expressed by behavioural repetitions, but testing sequences accompanied by smiling / laughter and careful monitoring of the experimenter’s actions were also present.
We conclude that the social side of imitation in its proactive form emerges early in human development, and has ancient evolutionary roots, i.e. it was likely present in the common ancestor of humans and chimpanzees. Since both enculturated and non-enculturated chimpanzees evidenced enjoyment, playfulness and strong social engagement when being imitated, it is unlikely that lack of shared intentionality and social motivation accounts for chimpanzees’ poorer performance in imitation learning tasks when compared to human children.
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