Understanding action beyond imitation: reversed compatibility effects of action observation in imitation and joint action.

A robust finding in imitation literature is that people perform their actions more readily if they are congruent with the behavior of another person. These action congruency effects are typically explained by the idea that the observation of someone else acting automatically activates our motor system in a directly matching way. In the present study action congruency effects were investigated between an imitation task and a complementary action task. Subjects imitated or complemented a virtual actor's grasp on a manipulandum. In both tasks, a color-cue could be presented forcing subjects to ignore the task rule and execute a predefined grasp. Reaction times revealed a reversal of congruency effects in the complementary action task, suggesting that subjects were able to circumvent the automatic tendency to copy actions or postures of another person. In 2 additional control experiments, congruency effects were replicated, and a Simon effect was identified to underlie faster responses in the imitation task. These results make a case against current theoretical views on imitation and direct matching in favor of more flexible models of perception-action coupling.