Cooperative and competitive contexts do not modify the effect of social intention on motor action.

In social interactions, the movements performed by others can be used to anticipate their intention. The present paper investigates whether cooperative vs competitive contexts influence the kinematics of object-directed motor actions and whether they modulate the effect of social intention on motor actions. An "Actor" and a "Partner" participated in a task consisting in displacing a wooden dowel under time constraint. Before this Main action, the Actor performed a Preparatory action which consisted in placing the dowel at the center of the table. Information about who would make the forthcoming Main action was provided only to the Actor through headphones. Results demonstrate an exaggeration of spatial and temporal actions' parameters when acting for the Partner, in cooperative, as well as in competitive context. This finding suggests that the motor manifestation of social intention is largely determined by non-conscious implicit processes that seem little influenced by the context of social interaction.