The roles of action selection and actor selection in joint task settings.

Studies on joint task performance have proposed that co-acting individuals co-represent the shared task context, which implies that actors integrate their co-actor's task components into their own task representation as if they were all their own task. This proposal has been supported by results of joint tasks in which each actor is assigned a single response where selecting a response is equivalent to selecting an actor. The present study used joint task switching, which has previously shown switch costs on trials following the actor's own trial (intrapersonal switch costs) but not on trials that followed the co-actor's trial (interpersonal switch costs), suggesting that there is no task co-representation. We examined whether interpersonal switch costs can be obtained when action selection and actor selection are confounded as in previous joint task studies. The present results confirmed this prediction, demonstrating that switch costs can occur within a single actor as well as between co-actors when there is only a single response per actor, but not when there are two responses per actor. These results indicate that task co-representation is not necessarily implied even when effects occur across co-acting individuals and that how the task is divided between co-actors plays an important role in determining whether effects occur between co-actors.