Route switching in imitation: should I stay or should I go?

Route switching in imitation: Should I stay or should I go? Alessia Tessari (alessia.tessari@unibo.it) Department of Psychology, viale Berti Pichat 5 40127 - Bologna, Italy Lucia Cretella (luciacretella@hotmail.com) Department of Psychology, viale Berti Pichat 5 40127 - Bologna, Italy Raffaella Rumiati (rumiati@sissa.it) Cognitive Neuroscience Sector, S.I. S.S. A. , Via Beirut 2-4 34135 - Trieste, Italy Abstract The dual-route models of action imitation predict that, normally, known actions are imitated by using a semantic route - i.e. by activating a representation of the action from memory - whereas unknown, new actions are reproduced by using a direct route - i.e. by performing a visuo-motor transformation of the input into an output. Here we aimed at establishing the nature of the dominant process used by healthy adult individuals in imitation. Participants performed an imitation task with both predictable switches and pseudorandom, unpredictable switches The predictable switches are less cognitively demanding, and allow the voluntary selection of the most suitable process for performing the task; whereas the unpredictable switches are more demanding and lead to a more intense use of strategies. We observed significant switch costs only in the predictable switch condition, when subjects had to rely on working memory to keep track of the underlying sequence, but not in the pseudorandom sequences, where participants could select the direct route to decrease the cognitive effort. These findings suggest that the semantic route is the dominant, more automatic and less-demanding process for action imitation. The strategic selection of route in action imitation and in monitoring behaviour seems to be an adaptive acquisition. Keywords: imitation, cognitive strategies, meaningful and meaningless actions, switching cost. Introduction Since Meltzoff and Moore (1977; 1983; 1989) discovered that infants can imitate facial expressions and hand gestures within a few hours of life, it has been widely accepted that imitation is an innate human ability. Many studies in both the context of social psychology (e.g. Dijksterhuis & Bargh 2001; Lakin et al. 2003) and cognitive neuroscience (e.g., Brass et al. 2000; Brass et al., 2005; Lhermitte et al. 1986; De Renzi et al. 1996) have suggested that imitation is a contagious and automatic process. Brass and colleagues (Brass et al. 2001; Brass et al. 2000), for example, showed that movement observation influences movement execution in a task in which the response is not related (i.e., a simple stimulus-response compatibility paradigm with finger movements), thus supporting an automatic tendency to imitate also in adults. Some authors have also shown that patients with frontal lesions suffer from imitation behaviour (Lhermitte et al. 1986; De Renzi et al. 1996) and they imitate the examiner’s movements even if instructed not to do so. It has been proposed that the deficit is caused by a lack of inhibition of the mediobasal frontal cortex on the parietal lobe. This effect is not to a general effect that involved overlearned skills but it is specific for inhibiting actions (Brass Derrfuss and von Cramon, 2005). In contrast, patients with ideomotor apraxia exhibit a dramatic reduction of their ability to imitate actions, and often to pantomime on verbal command and visually presented objects (De Renzi et al. 1980), in particular after lesions of the left inferior posterior parietal cortex (e.g. Goldenberg and Hagmann 1997; Buxbaum et al. 2005; Tessari et al. 2007). Models of imitation Many cognitive models have been put forward in order to explain imitative behaviours in humans. They range along a continuum. On the one end there is the direct matching approach (Prinz 1997; Hommel, Musseler, Aschrsleben and Prinz 2001), stating that observing the effect of an action facilitates its execution because perception and action planning share a common representational code. In the middle, the Active Intermodal Mapping (Meltzoff & Moore 1977; 1997), suggesting that imitation is a matching-to- target process, based on the proprioceptive feedback loop that allows infants’ motor performance to be evaluated against the perceived target. On the other end of the continuum, there are theories that require more than a simple process. One such theory is the goal-directed theory (Bekkering, Wohlschlager and Gattis, 2000), according to which imitation is decomposition-reconstruction process dependent on sub-goals hierarchically organized (i.e. the objects to which the actions are directed, the agents that perform actions, or the movement) and on cognitive