Facilitation effect of observed motor deviants in a cooperative motor task: Evidence for direct perception of social intention in action

Abstract

Spatiotemporal parameters of voluntary motor action may help optimize human social interactions. Yet it is unknown whether individuals performing a cooperative task spontaneously perceive subtly informative social cues emerging through voluntary actions. In the present study, an auditory cue was provided through headphones to an actor and a partner who faced each other. Depending on the pitch of the auditory cue, either the actor or the partner were required to grasp and move a wooden dowel under time constraints from a central to a lateral position. Before this main action, the actor performed a preparatory action under no time constraint, consisting in placing the wooden dowel on the central location when receiving either a neutral (“prêt”–ready) or an informative auditory cue relative to who will be asked to perform the main action (the actor: “moi”–me, or the partner: “lui”–him). Although the task focused on the main action, analysis of motor performances revealed that actors performed the preparatory action with longer reaction times and higher trajectories when informed that the partner would be performing the main action. In this same condition, partners executed the main actions with shorter reaction times and lower velocities, despite having received no previous informative cues. These results demonstrate that the mere observation of socially driven motor actions spontaneously influences the low-level kinematics of voluntary motor actions performed by the observer during a cooperative motor task. These findings indicate that social intention can be anticipated from the mere observation of action patterns.

Keywords:

• Perception
• Vision
• Sequential action
• Observation
• Social intention
• Cooperative task

Notes

¹Put at the forefront of the neuroscientific debate on intentionality by Jacob and Jeannerod (2005), Robert Louis Stevenson's story of “split personality” presents Dr. Jekyll, alias Mr. Hyde, a renowned surgeon who performs appendectomies on his anesthetized patients to heal them during the day, but to murder them during the night. He thus executes the same motor sequence during the day and at night, whereby he grasps his scalpel and applies it to the same bodily part of two different persons. According to Jacob and Jeannerod, Dr. Jekyll's motor intention is the same as Mr. Hyde's, although Dr. Jekyll's social intention (improving patient's health) clearly differs from Mr. Hyde's social intention (enjoying victim's agony). Social intention was thus thought to be hardly identifiable from movement characteristics.

Additional information

Funding

This study was supported by grants from the Programme d'Investissements d'Avenir [grant number ANR-11-EQPX-0023], [grant number FEDER SCV-IRDIVE], and from Charles de Gaulle–Lille 3 University.