Stopping movements: when others slow us down.

Previous research has shown that performing joint actions can lead to the representation of both one's own and others' actions. In the present study we explored the influence of co-representation on response stopping. Are joint actions more difficult to stop than solo actions? Using a variation of the stop-signal task, we found that participants needed more time to stop a planned joint action compared with a planned solo action (Experiment 1). This effect was not observed when participants performed the task in the presence of a passive observer (Experiment 2). A third transcranial magnetic stimulation experiment (Experiment 3) demonstrated that joint stopping recruited a more selective suppression mechanism than solo stopping. Taken together, these results suggest that participants used a global inhibition mechanism when acting alone; however, they recruited a more selective and slower suppression mechanism when acting with someone else.