Action prediction modulates self-other integration in joint action

People often coordinate actions with others, requiring an adjustable amount of self-other integration between actor's and co-actor's actions. Previous research suggests that such self-other integration (indexed by the joint Simon effect) is enhanced by agent similarity of the co-actor (e.g., high in intentionality). In this study, we aimed to extend this line of research by testing whether experiencing agency over a co-actor's actions (vicarious agency) and/or action prediction strengthens the joint Simon effect. For this purpose, we manipulated experienced agency by varying the experienced control over a co-actor's actions (Experiment 1), and action prediction regarding the co-actor's actions (Experiment 2). Vicarious agency could effectively be induced, but did not modulate the size of the joint Simon effect. The joint Simon effect was decreased when the co-actor's actions were unpredictable (vs. predictable) during joint task performance. These findings suggest social agency can be induced and effectively measured in joint action. Action prediction can act as an effective agency cue modulating the amount of self-other integration in joint action.