In joint action, multiple people coordinate their actions to perform a task together. This often requires precise temporal and spatial coordination. How do co-actors achieve this? How do they coordinate their actions toward a shared task goal? Here, we provide an overview of the mental representations involved in joint action, discuss how co-actors share sensorimotor information and what general mechanisms support coordination with others. By deliberately extending the review to aspects such as the cultural context in which a joint action takes place, we pay tribute to the complex and variable nature of this social phenomenon.

When performing joint actions, people modulate instrumental actions to provide additional information for a coactor (Pezzulo, Donnarumma, & Dindo, 2013). Similarly, demonstrators adjust instrumental actions to make them more informative for novice learners (Brand, Baldwin, & Ashburn, 2002). It is unknown whether the kinematic modulations performed to facilitate prediction in joint action coordination and the modulations performed to transmit information about the structure of novel actions are unique, or whether a general type of modulation can take on multiple functions. The present study therefore investigated whether there are unique kinematic markers for demonstration and for different types of joint action. In three experiments participants performed a virtual xylophone task, where they played simple xylophone melodies either alone, for a learner watching them, or together with another participant, while their movements were recorded. Participants increased movement amplitude during joint action and during demonstration. However, during joint action, participants modulated specific velocity parameters depending on whether their joint action partner knew or did not know the action sequence to be performed. The results demonstrate that there are specific kinematic cues to communicate the time and location of upcoming actions to a joint action partner but that there are no unique kinematic cues expressing the "pedagogical" intentions of a demonstrator. (PsycINFO Database Record

In joint performances spanning from jazz improvisation to soccer, expert performers synchronize their movements in ways that novices cannot. Particularly, experts can align the velocity profiles of their movements in order to achieve synchrony on a fine-grained time scale, compared to novices who can only synchronize the duration of their movement intervals. This study investigated how experts’ ability to engage in velocity-based synchrony affects observers’ perception of coordination and their aesthetic experience of joint performances. Participants observed two moving dots on a screen and were told that these reflect the hand movements of two performers engaging in joint improvisation. The dots were animated to reflect the velocity-based synchrony characteristic of expert performance (in terms of jitter of the velocity profile: Experiment 1, or through aligning sharpness of the velocity profile: Experiment 2) or contained only interval-based synchrony. Performances containing velocity-based synchrony were judged as more coordinated with performers rated as liking each other more, and were rated as more beautiful, providing observers with a stronger aesthetic experience. These findings demonstrate that subtle timing cues fundamentally shape the experience of watching joint actions, directly influencing how beautiful and enjoyable we find these interactions, as well as our perception of the relationship between co-actors.

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