Effector- and target-independent representation of observed actions: evidence from incidental repetition priming

Simulation mechanisms are thought to play an important role in action recognition. On this view, actions are represented through the re-enactment of the observed action. Mirror neurons are thought to be the neuronal counterpart of such a process, and code actions at a rather abstract level, often generalizing across sensory modalities and effectors. In humans, attention has been focussed on the somatotopic, effector dependent representation of observed actions in the mirror system. In this series of behavioural studies, we used incidental repetition priming to determine to which degree the cognitive representation of observed actions relies on effector- and target-dependent representations. Participants were presented with images depicting meaningless or meaningful actions and pressed a button only when presented with a meaningful action. Images were classified as depicting a repeated or new action, relative to the previous image in the trial series. In the first experiment, we demonstrate a priming effect based on the repetition of an action, performed by the same effector over the same target object. In the second experiment, we demonstrate that this facilitation holds even when the same action is performed over a different target object. Finally, in the third experiment we show that the action priming effect holds even when the same action is accomplished with different effectors. These results suggest the existence of a cognitive representation of actions, automatically activated during observation, which is abstract enough to generalize across different targets for that action and different effectors performing that action.