The Chameleon effect in Capuchin Monkeys

Imitation, as you probably know, has received considerable attention during the past 20 years or so because it was first argued that it was a uniquely human psychological mechanism that could partly explain the development of human material culture (see Whiten et al. 2004 for a review with historical perspective). In this long debate, imitation has come to acquire a technical definition: that of learning by observation a novel mean to reach a particular goal. While the discussion of whether non-human animals are able to imitate in this sense is still going on, a recent study by Annika Paukner, Stephen J. Suomi, Elisabetta Visalberghi and Pier F. Ferrari has challenged the human uniqueness of yet another form of imitation: the chameleon effect.

As its name indicate, the chameleon effect (dubbed after the Woody Allen movie Zelig, see movie below) refers to the "nonconscious mimicry of the postures, mannerisms, facial expressions, and other behaviors of one's interaction partners, such that one's behavior passively and unintentionally changes to match that of others in one's current social environment."(Chartrand & Bargh 1999) The chameleon effect is known to influence the social relationship between people: to smoothen relations, increase likeliness between individuals and increase empathic dispositions. But is the chameleon effect the consequence of a species typical disposition linked to our unique communicative abilities for instance, or is it shared with our close relatives and therefore linked to more general aspect of social behaviours?

[Beginning of Woody Allen's Zelig movie.]

In a first experiment, Paukner et al. showed that Capuchin monkeys prefer to look at experimenters imitating them playing with a ball, rather than experimenters playing with the ball but not trying to imitate their own actions. In a second experiment they showed that Capuchins prefer to stay closer to and to follow imitators rather than stay and follow controls (this is not linked to looking time, see experiment 3). Finally, they showed that monkeys prefer to exchange tokens with imitators rather than non imitators (again with appropriate controls, see experiment 5).

In my opinion these results are important because they call for a clear distinction between imitation as a learning mechanism (conscious, intentional, goal directed, potentially involved in the evolution of material culture and not obviously socially related) and imitation as a chameleon effect (unconscious, non intentional, non goal directed, not essentially involved in material culture and socially related). In some experiments both types of imitation may contribute in different respects to the observed behavioural pattern, depending on the difficulty of the task at hand. For instance, in some experiments monkeys, after having observed a demonstrator, are required to open a box by either pushing or pulling a door (e.g. Bugnyar & Huber 1997). In this setting, results show that monkeys tend to preferentially use the observed action rather than its alternative but given the simplicity of the task, one can wonder if their copying of another's action is linked to learning or to social dispositions to match other's actions. Pushing or pulling could be activated by their unintentional social disposition to match a conspecific behaviour rather than their intention to reach a particular goal using a specific mean.

This distinction is essential to people interested in cultural evolution because social learning, more than social motivations, can give rise to the spread of new adaptive behaviours wheareas social motivations, more than social learning, can explain the stability of group specific behaviours.

References

Whiten, A., Horner, V., Litchfield, C. A. & Marshall-Pescini, S. 2004 How do apes ape? Learn Behav 32, 36-52.

Paukner, A., Suomi, S. J., Visalberghi, E., & Ferrari, P. F. (2009). Capuchin Monkeys Display Affiliation Toward Humans Who Imitate Them. Science, 325(5942), 880-883.

Chartrand, T. L., & Bargh, J. A. (1999). The Chameleon Effect: The Perception-Behavior Link and Social Interaction. Journal of Personality & Social Psychology, 76(6), 893-910.

Bugnyar, T., & Huber, L. (1997). Push or pull: an experimental study on imitation in marmosets. Animal Behaviour, 54(4), 817-831.