Distinct Kinematic Markers of Demonstration and Joint Action Coordination? Evidence From Virtual Xylophone Playing

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. Public Significance Statement This study demonstrates that people adjust their movements to communicate task relevant information, in various social interactions. Movement height is increased both to coordinate with a task partner and to demonstrate an action to a novice learner. However, changes in velocity are specific to joint action coordination and depend on the partner's state of knowledge. The results raise the possibility that information communicated in joint action coordination could also be useful for learning.