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Andrew Chang, Steven R Livingstone, Dan J Bosnyak, and Laurel J Trainor (2017)

Body sway reflects leadership in joint music performance

Proceedings of the National Academy of Sciences of the United States of America, 114(21):E4134–E4141.

The cultural and technological achievements of the human species depend on complex social interactions. Nonverbal interpersonal coordination, or joint action, is a crucial element of social interaction, but the dynamics of nonverbal information flow among people are not well understood. We used joint music making in string quartets, a complex, naturalistic nonverbal behavior, as a model system. Using motion capture, we recorded body sway simultaneously in four musicians, which reflected real-time interpersonal information sharing. We used Granger causality to analyze predictive relationships among the motion time series of the players to determine the magnitude and direction of information flow among the players. We experimentally manipulated which musician was the leader (followers were not informed who was leading) and whether they could see each other, to investigate how these variables affect information flow. We found that assigned leaders exerted significantly greater influence on others and were less influenced by others compared with followers. This effect was present, whether or not they could see each other, but was enhanced with visual information, indicating that visual as well as auditory information is used in musical coordination. Importantly, performers’ ratings of the “goodness” of their performances were positively correlated with the overall degree of body sway coupling, indicating that communication through body sway reflects perceived performance success. These results confirm that information sharing in a nonverbal joint action task occurs through both auditory and visual cues and that the dynamics of information flow are affected by changing group relationships.

motion capture, Granger causality, leadership, perception & action, body sway, music performance, joint action
People perform tasks in coordination with others in daily life, but the mechanisms are not well understood. Using Granger causality models to examine string quartet dynamics, we demonstrated that musicians assigned as leaders affect other performers more than musicians assigned as followers. These effects were present during performance, when musicians could only hear each other, but were magnified when they could also see each other, indicating that both auditory and visual cues affect nonverbal social interactions. Furthermore, the overall degree of coupling between musicians was positively correlated with ratings of performance success. Thus, we have developed a method for measuring nonverbal interaction in complex situations and have shown that interaction dynamics are affected by social relations and perceptual cues.