Avoiding Accidents at the Champagne Reception: A Study of Joint Lifting and Balancing

Using a lifting and balancing task, we contrasted two alternative views of planning joint actions: one postulating that joint action involves distinct predictions for self and other, the other postulating that joint action involves coordinated plans between the coactors and reuse of bimanual models. We compared compensatory movements required to keep a tray balanced when 2 participants lifted glasses from each other’s trays at the same time (simultaneous joint action) and when they took turns lifting (sequential joint action). Compared with sequential joint action, simultaneous joint action made it easier to keep the tray balanced. Thus, in keeping with the view that bimanual models are reused for joint action, predicting the timing of their own lifting action helped participants compensate for another person’s lifting action. These results raise the possibility that simultaneous joint actions do not necessarily require distinguishing between one’s own and the coactor’s contributions to the action plan and may afford an agent-neutral stance.