Recent studies provide experimental evidence for joint rushing - the phenomenon that participants in rhythmic group activities unintentionally increase their tempo. We hypothesized that joint rushing arises from the combined workings of established sensorimotor synchronization mechanisms (e.g., phase and period correction) with a simple phase advance mechanism that has been studied in mass-synchronizing insects. We invited musicians and non-musicians to participate in three tapping experiments. Participants were asked to continue to produce a constant target tempo alone (solo) or together with a partner (joint). The results show that joint rushing induces a lasting period correction but stops when auditory feedback of the partner’s taps is removed. Musical training reduced the magnitude of joint rushing but did not eliminate it. These results are consistent with our hypothesis that joint rushing occurs because adjustments induced by a simple phase advance mechanism alter the period of internal timekeeping.

When people perform joint actions together, task knowledge is sometimes distributed asymmetrically such that one person has information that another person lacks. In such situations, interpersonal action coordination can be achieved if the knowledgeable person modulates basic parameters of her goal-directed actions in a way that provides relevant infor- mation to the less knowledgeable partner. We investigated whether systematic violations of predicted movement duration provide a sufficient basis for such communication. Results of a joint movement task show that knowledgeable partners spontaneously and systematically violated the pre- dictions of Fitts’ law in order to communicate if their partners could not see their movements. Unknowing partners had a benefit from these violations and more so if the violations provided a good signal-to-noise ratio. Together, our findings suggest that generating and perceiving systematic deviations from the predicted duration of a goal-directed action can enable non-conventionalized forms of communication during joint action.

Creative thought relies on the reorganisation of existing knowledge. Sleep is known to be important for creative thinking, but there is a debate about which sleep stage is most relevant, and why. We address this issue by proposing that rapid eye movement sleep, or REM, and non-REM sleep facilitate creativity in different ways. Memory replay mechanisms in non-REM can abstract rules from corpuses of learned information, while replay in REM may promote novel associations. We propose that the iterative interleaving of REM and non-REM across a night boosts the formation of complex knowledge frameworks, and allows these frameworks to be restructured, thus facilitating creative thought. We outline a hypothetical computational model which will allow explicit testing of these hypotheses.

Effective social co-ordination benefits from mentally representing a partner’s actions. Chimpanzees can successfully work together, but the cognitive mechanisms they employ to aid social co-ordination remain unclear. Studies of action planning show that, like humans, chimpanzees demonstrate the end-state-comfort effect; considering the end of an action sequence during motor-planning, e.g. using an initially awkward grasp when handling an overturned glass to facilitate how it will end up being held. Human research shows that we extend this to a partner; we pass objects in a way that facilitates the action to be performed with them. Here, we assessed the location in which chimpanzees passed a tool to an experimenter to investigate action accommodation. We manipulated experimenter hand location and their ease of access to locations and found some effect on passing behaviour indicating that, under certain conditions, chimpanzees consider a partner’s actions when planning their own actions in a co-ordination context.

Can people interpret communicative action modulations in terms of the actor’s distal goal? We investigated situations in which the proximal goal of an action (i.e., the movement endpoint) does not overlap with its distal goal (i.e., a final location beyond the movement endpoint). Participants were presented with animations of an object being moved at different velocities towards a designated endpoint. The distal goal, however, was for the object to be moved past this endpoint, to one of two occluded final locations. Participants were asked to select the location which they considered the likely distal goal of the action. As predicted, participants detected differences in movement velocity and, based on these differences, systematically mapped the movements to the two distal goal locations. These findings extend previous research on sensorimotor communication by demonstrating that communicative action modulations are not restricted to proximal goals but can also contain information about distal goals.