Dyads use heuristics to minimise time costs during joint action.

Research on joint action planning has demonstrated that, when acting with others, individuals will choose more effortful actions if it improves co-efficiency by reducing the overall effort exerted by the group. However, because these studies use actions for which time and effort costs are confounded, it is unclear which costs participants sought to minimise and what processes underlie decision-making about individual contributions to joint actions. Across three experiments, we tested (1) whether dyads aim to minimise effort vs. time costs (Experiments 1-2) and (2) whether individuals choose actions based on a rational, deliberative process or a heuristic (Experiment 3). Data from a joint object-dragging computer task revealed that participants chose to drag objects to the closer of two goals even when it required more effort from the dyad (Experiments 1-2). Participants preferred closer goals when time and effort costs were equal (Experiment 3a), but only when the objects' locations were salient (Experiment 3b). Together, these results suggest that: (1) individuals minimise time, rather than effort, when sharing object-moving tasks, and (2) they do so - at least in part - by using distance as a heuristic. Our findings also replicate and extend earlier work showing that people prefer acting together versus alone, even when this is less efficient.