How Action Adapts to Social Context: The Movements of Musicians in Solo and Ensemble Conditions

When people perform a task as part of a joint action, their behavior is not the same as it would be if they were performing the same task alone: it is adapted to facilitate shared understanding (or sometimes to prevent it). Joint performance of music offers a test bed for ecologically valid investigations of the way non-verbal behavior facilitates joint action. Here we compare the expressive of violinists when playing solo Vs. in the string quartet music ensemble. The first and second violinists of a famous concert string quartet were asked to play the same musical fragment in a solo condition and with the quartet. Synchronized multimodal recordings have been created from the performances, using a specially developed software platform. The differences are not obvious to untrained observers but they are discriminated by musicians, and appropriate measures show that they exist. In particular, using an appropriate measure of entropy shows that head movements are more predictable in the quartet scenario. The change does not, as might be assumed, entail markedly reduced expression. The data pose provocative questions about joint action in realistically complex scenarios.