Using Granger Causality to quantify information flow between the sounds of ensemble musicians
Presenter Name:Lucas Klein
Co-Authors:Emily Wood, Dan Bosnyak, Laurel Trainor
Abstract:Groups of musicians playing together must coordinate without speaking, which requires non-verbal communication. Although large orchestras rely on a conductor to unify their playing, musicians in small ensembles must listen closely to each other and match their playing to create a cohesive musical product; they must anticipate what each performer will play next and adapt accordingly. Our previous research used Granger causality to examine functional directed connectivity between the body sway of musicians in a string quartet. The body sway of secretly assigned leaders influenced that of followers more than vice versa, even when they could not see each other. This begs the question: is information that followers use to anticipate leaders’ playing also contained within the sound itself? To investigate this, we asked professional violinists to audio record themselves playing along with a recording of “Danny Boy” while attempting to match its expressive features such as dynamic changes and expressive timing. We extracted amplitude envelopes from both the performances and recordings and found that Granger causality values from the recording to the performance a) were larger than for vice versa and b) decreased over the course of 8 trials. The more familiar musicians became with the recording, the less they needed to predict from the recording what was coming next. The results confirm the efficacy of Granger causality to quantify causal relationships between instruments in an ensemble using amplitude envelopes. They also shed light on learning, familiarity and planning processes that may facilitate coordination between musicians during group performances.