ΜΑΘΗΣΗ ΜΕΣΩ ΜΙΜΗΣΗΣ: Παιδιά vs. Χιμπατζήδες [ΑΡΘΡΟ] 2

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Mark Nielsen (2009) The imitative behaviour of children and chimpanzees: A window on the transmission of cultural traditions. Revue de primatologie [On-line], 1, document 5, 08 octobre 2009. URL : http://primatologie.revues.org/254

[...] a capacity for imitation has been well documented in chimpanzees (for reviews see Whiten, 2005; Tomasello and Carpenter, 2005b). Moreover, the results of some controlled experiments indicate that the imitative behaviour of children and chimpanzees may not be all that dissimilar. For example, Horner and Whiten (2005) showed wild born chimpanzees and 3- to 4-year-old children how to obtain a reward

from an opaque box. A human model first removed a bolt on the top of the box, revealing a hole into which a stick was inserted. The model then opened a door located on the front of the box and, by inserting the stick, retrieved the reward (food for the chimpanzees, a sticker for the children). Because the box was opaque the subjects could not see the causal relation between the actions and the desired outcome. When given the box to explore, both chimpanzees and children copied what the model had done. They first removed the bolt and placed the stick into the top hole and then opened the door and placed the stick into the hole at the front. The

authors interpreted this as evidence of imitation in both species. However, Horner and Whiten also documented some interesting inter-species differences.

In addition to the opaque box, Horner and Whiten (2005) tested their subjects for imitation using a ransparent box. The actions occurring inside the box could now be seen, making it obvious that when the stick was inserted into the top hole it struck a barrier and made no contact with that part of the apparatus from which the reward could be retrieved. The action involving the top hole could be clearly seen to have no causal relation to the desired outcome. When the same actions that had been modeled on the opaque box were modeled on the transparent box, the chimpanzees ignored the first action and instead copied only the model’s insertion of the tool into the front hole. They focused principally on replicating the actions that were causally related to the desired outcome. By contrast, the children imitated the model’s entire sequence of actions, including the obviously irrelevant insertion of the stick into the top hole.

The findings of Horner and Whiten (2005) reflect those in other studies that have found a far greater fidelity in copying behaviour by children compared to other apes (Tomasello et al., 1993; Whiten et al., 1996; e.g., Call et al., 2005; Tennie et al., 2006). Indeed, unlike chimpanzees, children consistently show a predilection for copying the specific means an adult uses to produce a particular outcome, even if a more efficient method is available. Research indicates that this predilection emerges during the second year.

[...]

In a cross-sectional study of children aged 12, 18, and 24 months, an adult model demonstrated how to open three novel boxes using an arbitrary object (e.g., a plastic block) to manipulate a switch located on the front of each box (Nielsen, 2006, Experiment 1). Correctly manipulating the switch, which was different for each box, disengaged a hidden latch and released the box’s lid, enabling a desirable toy to be retrieved. The children could have copied the model’s behavioral means of activating the switches (i.e., used the object) or they could have devised their own means (i.e., used their hands – something the model did not do). Two control conditions established that children of all age groups could easily activate the switches by hand if shown how but that they would not spontaneously attempt to do so, either by hand or by object, in the absence of modeling. 

Surprisingly, 12-month-olds opened as many boxes as did 24-month-olds when the model used an object to activate the switches. This counterintuitive finding can be explained by the specific actions the children employed when attempting to get the boxes open. Whereas the 24-month-olds tried to open every box using an object, as was modeled to them, the 12-montholds only attempted to open the boxes with their hands. Eighteen-month-olds showed reactions that were intermediate between the older and younger age groups. All age groups were equally successful at getting the boxes open, but because the 24-month-olds, and to a lesser extent the 18-month-olds, persisted in using the objects, their ability to activate the switches was diminished. With regard to getting the boxes open, these children would have been better off employing their own behavioral means of activating the switches (i.e., their hands) and ignoring the actions used by the model.

In a subsequent study (Nielsen, 2006, Experiment 2), 12-month-olds did use an object in an attempt to activate the switches, but only when the model had successfully used an object after first ‘attempting but failing’ to activate the switches by hand. Thus, it appears that 12-montholds did not fail to copy the model’s object use because they could not use the object, but rather because they did not interpret this action to be the most efficient alternative available (see also Gergely et al., 2002; Gergely, 2003).

Thus, from around the middle of their second year children begin to show a tendency for copying the specific actions of an adult model, even if by doing so they fail to achieve the modeled outcome. This tendency is not strong at the beginning of the second year. It was rare for the 12-month-olds in Nielsen (2006) to attempt to touch a switch using an object; they used their hands instead. Thus, although these toddlers attempted to reproduce the result of the model’s actions (i.e., opening the boxes), they did not copy the behavioral means used by the model (i.e., using an object). It appears that 12-month-olds, like chimpanzees, are more prone

than 18- and 24-month-olds to ignore seemingly irrelevant actions and to devise their own ways of bringing about the modeled outcome. How might we explain this pattern of findings? 

A growing body of research has shown that the generation of action shares common neural and cognitive mechanisms with the recognition of actions performed by others (for reviews see chapters in Hurley and Chater, 2005). The production of matched behaviour – forming an equivalence between what we see and what we do – thus appears to rely on the same capacities as recognising matched behaviour – detecting an equivalence between what we do and what we see (Nadel, 2002; Mitchell, 2002; Meltzoff and Decety, 2003). Perhaps chimpanzees and young human children are not particularly good at matching their own actions to the actions they have seen performed by others.

[...]

There is a long-standing though often neglected view that imitation can serve two distinct but complementary developmental functions: A cognitive function that promotes learning about events in the world and an interpersonal function that promotes children’s sharing of experience with others (Baldwin, 1894; Wallon, 1934; Uzgiris, 1981; Mitchell, 1987; Meltzoff, 1990; Meltzoff and Gopnik, 1993; Nadel et al., 1999; Tomasello, 1999a). Uzgiris (1981) argued that as children get older their motivation to copy others changes according to these two functions. Young toddlers are primarily motivated to imitate in order to acquire

new skills whereas older toddlers may imitate in the same context in order to satisfy social motivations.

19 The variant nature of the functions of imitation is highlighted by changes during the second year in the way pre-verbal infants interact with each other. Towards the middle of the second year children begin to coordinate their own actions with the thematic specifics of a social partner’s play, and this helps generate and sustain ongoing interaction (Nadel and Baudonnière, 1980; 1982; Nadel et al., 1983; Eckerman et al., 1989; Eckerman and Didow, 1989; Nadel and Fontaine, 1989). Children show a preference for engaging with objects that are similar to ones chosen by their play partner, and tend to use the common object in a similar way. When this copying behavior is performed in concert with the play partner, and the partners do not solely adopt one role but alternate between model and imitator, it is referred to as synchronic imitation (e.g., Asendorpf and Baudonnière, 1993; Nadel, 2002).

In controlled studies of synchronic imitation, an adult experimenter continuously models simple actions on a series of objects (e.g., tapping a toy hammer on the ground) to children who have a duplicate of the object available to them (Asendorpf et al., 1996; Nielsen and Dissanayake, 2004). To be classified as synchronic imitation, children must not only reproduce the actions of the experimenter but do so continuously and simultaneously for a certain amount of time. Using this approach, Nielsen and Dissanayake (2004) assessed 86 toddlers for synchronic imitation at intervals of three months from 12 to 24 months of age. Toddlers

sat on a play mat opposite an experimenter. The experimenter took an object and offered the toddler a duplicate of the object. The experimenter continuously modeled an action for 15 seconds and then performed a second action with the same object for a further 15 seconds. This procedure was repeated on an additional three objects. Toddlers were classified as imitating synchronically if they took the duplicate object and, while the experimenter was modeling the action, copied him continuously for at least 3 seconds (following Asendorpf et al., 1996).The duration of the sequence was coded for as long as the toddler maintained imitation of the modeled action and continued to look at the experimenter at least once every ten seconds.

When aged 12 and 15 months, the infants exhibited little to no synchronic imitation. It was not until 18 months of age that they began to exhibit sustained imitative sequences, and by the 24-month session toddlers were spending approximately one third of the 120-second episode engaging in synchronic imitation with the experimenter. Importantly, the actions Nielsen and Dissanayake (2004) used in administration of the synchronic imitation task were simple (e.g., banging a hammer on the ground). It is thus unlikely that the low exhibition of synchronic imitation by 12 and 15 month olds can be attributed to changes in their ability to either

produce or copy the modelled actions. Indeed, Nielsen and Dissanayake noted that when the children were younger it was not uncommon for them to reproduce the target actions of the experimenter during administration of the task; they just did not copy him continuously and simultaneously. When younger, the children engaged in imitation but not synchronic imitation.

It has thus been argued that when toddlers engage in synchronic imitation they do so primarily because they want to be social and to interact with the experimenter (Nielsen and Dissanayake, 2003; Nielsen et al., 2006; Nielsen and Slaughter, 2007; Slaughter et al., 2008).

Uzgiris (1981) also speculated that because young toddlers engage in imitation primarily to promote learning about events in the world they will focus more on copying what was done rather than copying the way it was done. Older toddlers, by contrast, will copy a model in order to engage socially and to sustain interaction. This speculation is reflected in the previously discussed findings from Nielsen (2006) where 12-month-olds, unlike 18- to 24-month-olds, tended not to use the same behavioral means as the model to bring about the target outcomes.

[...]

At the time of writing, only two empirical studies had experimentally manipulated the sociability of a model in order to investigate how differences in the availability of social interaction impacts children’s copying behaviour (Gergely and Király, 2004, May; Nielsen, 2006; for a more recent study see Nielsen et al., 2008). In Nielsen (2006, Experiment 3), 18- and 24-month-old children were shown how a miscellaneous object could be used to open each of the three previously-introduced boxes (see p. 7; section titled “Copying Actions Over Outcomes”). In a ‘social’ condition the model was typically engaging and interactive

whereas in an ‘aloof’ condition the model acted in a detached and disinterested manner: She avoided eye contact and did not direct any attention towards the child. The social disposition of the model affected the children differently. Eighteen-month-olds opened the same number of boxes regardless of condition, but were more likely to copy the model’s object use when she acted socially. In contrast, 24-month-olds used an object at equivalent rates across conditions but opened less boxes when the model was aloof and unengaging. Following Uzgiris (1981), it was argued that 18-month-olds copied the specific actions of the social model in order to sustain interaction and convey mutuality with her. In the absence of social reinforcement, they

focused instead on copying what was done rather than copying the way in which it was done. For 24-month-olds, the lack of social interaction provided by the aloof model reduced their motivation to produce the modelled outcome. Rather, they copied her specific actions in an attempt to initiate interaction. These arguments are in line with perspectives that assert a social and communicative role in young children’s copying behaviour (for an alternative view see Gergely and Csibra, 2005; Csibra and Gergely, 2006).

No study has directly manipulated the sociability of the model in any test of great ape imitation. Nevertheless, there are hints in the literature to suggest that apes do not treat imitative exchanges in the same communicative manner as young children. Two species of chimpanzee (Pan troglodytes and Pan paniscus) and 18-month-old human children were observed whilst engaged in an object-directed imitation task involving an adult human model (Carpenteret al., 1995). All three species showed episodes of joint attention involving the model and the objects. However, the bouts of joint attention were longer in the children and they spent more time looking at the model’s face. Tomasello, Carpenter, Call, Behne and Moll (2005) suggest that these inter-species differences might have arisen because the chimpanzees were looking at the model to see what she was doing or was likely to do next, whereas the children looked to share interest. They further suggest that this might indicate that although apes know that others have goals and perceptions, unlike children, they have little desire to share them. 

If chimpanzees are not inclined to use imitation as a mechanism for social interaction, longlasting interactions about an object through the alternation of imitating and being imitated are unlikely to be built. That is, evidence of synchronic imitation in chimpanzees is likely to prove elusive. Recent evidence that chimpanzees, unlike 18- and 24-month-old children, are uninterested in social games substantiates this point (Warneken et al., 2006). It is also likely that structured comparison of the responses of children and chimpanzees to being imitated will

yield communication-based, inter-species differences. For example, as part of the previously introduced longitudinal study (Nielsen and Dissanayake, 2003; 2004), we tested young children for imitation recognition using a procedure similar to the one employed to assess chimpanzee imitation recognition (Nielsen et al., 2005). Anecdotally, the children clearly found it amusing when they understood that they were being imitated. Testing frequently developed into a game, accompanied by giggles and squeals of delight. The children would

even go to great lengths to produce sequences of behaviour that were as difficult as possible for the experimenter to copy. Cassie, the captive chimpanzee, showed none of these signs. 

[...]

From the middle of their second year children will persist in reproducing the exact, at times maladaptive, actions of an adult model – even at the expense of producing the outcome of those actions. Comparable evidence of this kind of imitative behaviour in our closest living relatives has not been forthcoming. That chimpanzees will not slavishly copy a model, as do human children, cannot be attributed to competence. Recall that in the study by Horner and Whiten (2005), when the box was opaque the chimpanzees copied the adult model’s full behavioural sequence – the redundant components were omitted only when the causal relation between the actions and their outcomes was made apparent. They were thus capable of performing the modelled actions. Evidence of imitation recognition also suggests that chimpanzees are not in some way deficient in matching across seen and felt modalities. Rather, the argument put forward here is that, unlike chimpanzees, children are motivated to copy others in order to be social and to promote shared experience with the model. This social motivation manifests itself in a pull towards copying how something was done rather than what was done. 

Over 5 million years of distinct evolutionary history has resulted in a seemingly infinite array of cultural variants in humans, and 39 in chimpanzees. Given the well-argued position that imitation is a fundamental component of the transmission of culture (e.g., Heyes, 1993; Tomasello, 1999a; Whiten et al., 2003; Whiten, 2005; Gergely and Csibra, 2005; Meltzoff, 2005), differences should prevail in the imitative behaviour of these two species. Based on the arguments presented here, the principle difference lies with a peculiarly human tendency to imitate actions over outcomes. For us, at least as children, means are more important than ends.

With regard to cultural traditions, this makes intuitive sense. If one thinks about distinguishing cultures, it is how things are done that is most relevant, not what is done. That the Japanese and the British drink tea provides far less insight into their respective cultural traditions than the way they do so. Doing things the way those around us do things lies at the heart of the transmission of culture. A tendency to behave in this way is evident in the way human children imitate from the middle of their second year.

It has been argued here that young children’s focus on copying actions over outcomes is a function of their motivation to be social and to interact with the model. The maturation of domain general cognitive abilities are likely to be important in the emergence of this motivation (Stone, 2005). Other components of development, such as emotional engagement (Hobson, 2004), intention reading (Tomasello, 1999b; Tomasello et al., 2005; Tomasello and Carpenter, 2005b) and receptivity to being taught (Gergely and Csibra, 2005; Csibra and

Gergely, 2006; Gergely and Csibra, 2006) may also play a role. Establishing which of these components of development (and others) determine why young children imitate in the way they do will no doubt form the foundation for much ongoing research and debate. The line between the imitative abilities of human children and chimpanzees remains somewhat blurred. The use of imitation as a form of communication may yet prove to be a distinguishing feature between our closest evolutionary relatives and us.