The role of group membership on the modulation of joint action.

Two experiments were conducted to assess whether the emergence of shared representations, as indexed by the joint Simon effect, is modulated by perceived group membership. In both experiments, participants were required to perform a Simon task along another person who was perceived as belonging either to the same group or to a different group. In Experiment 1, ingroup-outgroup discrimination was obtained by dividing participants into two groups based on a superficial criterion; in Experiment 2, it was obtained by manipulating the interdependence experienced by the two acting individuals. The mere social categorization of co-acting participants into groups did not modulate the joint Simon effect which was observed even when participants believed to perform the task along with an individual belonging to a different social group (Experiment 1). On the contrary, the effect was modulated by perceived interdependence, with a null effect when participants experienced negative interdependence (Experiment 2). These results suggest that when acting in a social context, by default, individuals may perceive positive interdependence with co-acting individuals, even when cooperation is not explicitly requested.