Imitation of hand and tool actions is effector-independent

Abstract

Following the theoretical notion that tools often extend one's body, in the present study, we investigated whether imitation of hand or tool actions is modulated by effector-specific information. Subjects performed grasping actions toward an object with either a handheld tool or their right hand. Actions were initiated in response to pictures representing a grip at an object that could be congruent or incongruent with the required action (grip-type congruency). Importantly, actions could be cued by means of a tool cue, a hand cue, and a symbolic cue (effector-type congruency). For both hand and tool actions, an action congruency effect was observed, reflected in faster reaction times if the observed grip type was congruent with the required movement. However, neither hand actions nor tool actions were differentially affected by the effector represented in the picture (i.e., when performing a tool action, the action congruency effect was similar for tool cues and hand cues). This finding suggests that imitation of hand and tool actions is effector-independent and thereby supports generalist rather than specialist theories of imitation.

Fig. 1

a Experimental setup. Participants were seated behind a table on which the manipulandum and a screen were placed. Actions were performed with either the right hand (left picture) or with a handheld tool (right picture). Stimuli were presented on a screen directly in front of the participant. b Starting picture representing the manipulandum with the actor’s hands out of view (left side) and example stimuli (right side) used in the tool cue, the hand cue, and the symbolic cue conditions. Participants were instructed to grasp the manipulandum with either a precision or a power grip depending on the color of the stimuli

Fig. 2

Reaction and movement times. Graphs at the left represent RTs and MTs to actions performed with the tool, and graphs at the right represent RTs and MTs to actions performed with the hand. Bars on the left represent actions in response to tool cues, bars in the middle represent actions in response to hand cues, and bars on the right represent actions in response to symbolic cues. Light bars represent congruent movements and dark bars incongruent movements. Error bars represent standard errors