Joint response-effect compatibility.

When performing jointly on a task, human agents are assumed to represent their coactor's share of this task, and research in various joint action paradigms has focused on representing the coactor's stimulus-response assignments. Here we show that the response-effect (R-E) contingencies exploited by a coactor also affect performance, and thus might be represented as if they were used by oneself. Participants performed an R-E compatibility task, with keypresses producing spatially compatible or incompatible action effects. We did not observe any R-E compatibility effects when the task was performed in isolation (individual go-no-go). By contrast, small but reliable R-E compatibility effects emerged when the same task was performed in a joint setting. These results indicate that the knowledge of a coactor's R-E contingencies can influence whether self-produced action effects are used for one's own motor control.