Clear and unequivocal evidence shows that observation of object affordances or transitive actions facilitates the activation of a compatible response. By contrast, the evidence showing response facilitation following observation of intransitive actions is less conclusive because automatic imitation and spatial compatibility have been confounded. Three experiments tested whether observation of a finger movement (i.e., an intransitive action) in a choice reaction-time task facilitates the corresponding finger movement response because of imitation, a common spatial code, or some combination of both factors. The priming effects of a spatial and an imitative stimulus were tested in combination (Experiment 1), in opposition (Experiment 2), and independently (Experiment 3). Contrary to previous findings, the evidence revealed significant contributions from both automatic imitation and spatial compatibility, but the priming effects from an automatic tendency to imitate declined significantly across a block of trials whereas the effects of spatial compatibility remained constant or increased slightly. These differential effects suggest that priming associated with automatic imitation is mediated by a different regime than priming associated with spatial compatibility.

Recent behavioral, neuroimaging, and neurophysiological research suggest a common representational code mediating the observation and execution of actions; yet, the nature of this representational code is not well understood. We address this question by investigating whether this observation-execution matching system (or mirror system) codes both the constituent movements of an action as well as its goal, and how such sensitivity is influenced by the topdown effects of instructions. Automatic imitation of observed finger actions was tested by manipulating whether the movements were biomechanically possible or impossible, while holding the goal constant. When no mention was made of this difference (Experiment 1), comparable automatic imitation was elicited from possible and impossible actions, suggesting that the actions had been coded at the level of the goal. When attention was drawn to the difference between possible and impossible movements (Experiment 2), only possible movements elicited automatic imitation. This sensitivity was specific to imitation, not affecting spatial S-R compatibility (Experiment 3). These results suggest that the human mirror system isautomatic imitation is modulated by top-down influences, coding actions in terms of both movements and goals depending on the focus of attention.