Twin peaks: An ERP study of action planning and control in coacting individuals

Previous studies have shown that perceiving another's actions activates corresponding representations in an observer's action system. The present study investigated how performing a task with another person affects action planning and control. Reaction times (RTs) and event-related potentials were measured while participants performed a go/no-go task alone and with another person. Three effects of acting together were observed. First, RTs were slowed when individuals had to respond to a stimulus referring to the other's action, suggesting that an action selection conflict occurred. Second, at frontal sites, a stimulus referring to the other's action elicited a similar electrophysiological response as a stimulus referring to one's own action. Finally, on no-go trials, P300 amplitude was significantly larger in a group setting, indicating that an action was suppressed. These findings provide evidence that individuals acting in a social context form shared action representations.