When do we simulate non-human agents? Dissociating communicative and non-communicative actions

Abstract

There is strong evidence that we automatically simulate observed behavior in our motor system. Previous research suggests that this simulation process depends on whether we observe a human or a non-human agent. Measuring a motor priming effect, this study investigated the question of whether agent-sensitivity of motor simulation depends on the specific action observed. Participants saw pictures depicting end positions of different actions on a screen. All postures featured either a human or non-human agent. Participants had to produce the matching action with their left or right hand depending on the hand presented on the screen. Three different actions were displayed: a communicative action (emblem), a transitive (goal-directed) action and an intransitive action. We found motor priming effects of similar size for human and non-human agents for transitive and intransitive actions. However, the motor priming effect for communicative actions was present for the human agent, but absent for the non-human agent. These findings suggest that biological tuning of motor simulation is highly action-selective and depends on whether the observed behavior appears to be driven by a reasonable goal.

Introduction

An extensive body of brain imaging research suggests that passive observation of human action leads to activation of brain areas that are also involved in motor preparation and execution (Buccino et al., 2001, Fogassi et al., 2005, Gallese et al., 1996, Gazzola et al., 2006, Grezes et al., 2003, Iacoboni et al., 1999). Furthermore, behavioral research strongly suggests that the observation of an action activates a corresponding motor representation in the observer. This phenomenon has been termed motor simulation (for an overview see Brass and Heyes, 2005 and Blakemore and Frith, 2005). Motor simulation is typically measured with a motor priming paradigm, in which participants have to carry out an instructed response while observing task-irrelevant congruent or incongruent actions (e.g., Brass, Bekkering, Wohlschläger, & Prinz, 2000). It has been demonstrated that the observation of a finger movement that corresponds to the instructed finger movement leads to facilitation of the response and observing a non-corresponding finger movement leads to interference (Bertenthal et al., 2006, Brass et al., 2000, Stürmer et al., 2000).