Communication in a string quartet

Casa Paganini, Uni of Genoa

As I mentioned in the earlier post from the International Symposium on Performance Science, string quartets seem to be fashionable in music psychology, and for good reasons. They are perhaps the prototype of a chamber music ensemble, with lots of great pieces written for them, they are of an optimal size for such studies, and of course there are many professional quartets that have worked together for years, making them extremely interesting topics for research on coordination and interaction. A new study from Genoa looks at communication in a string quartet, using a cool setup.

First of all, I must say that the research facilities for the infoMus group are the best I’ve seen anywhere: they have converted an old historical building into a concert hall and a music lab, Casa Paganini. Labelling mocap marker data would not feel too tedious if you could do it surrounded by those frescos!

In this study, the quartet is motion captured, and the kinematics of their head movements (in relation to a common central point) are then used to measure how much each of them influences the others. The measure they use is called Granger causality, and it works simply by looking at whether time series A (say, the head movements of the first violin player) will help in predicting time series B (the head movements of the cellist). If so, then we can say that A “Granger-causes” B. This is a measure of influence or “connection” that is often used in econometrics (does price of oil G-cause employment) and recently also in brain research looking for connections between parts of the brain (is activity in one part G-caused by activity in another part).

From the Granger causality measures, the authors directly get the inter-musician communication measures (IMC), and the composite measure of MDF or “musician driving force”, which is a subtraction of the influence that A has on B from the influence B has on A, to see who influences others more.

One very clear result was that the musicians seemed to communicate much more when they were playing highly complex passages, compared to when they were playing simple ones. As expected, the first violin was usually the one driving the others, the clearest leader. Especially this second result serves as a “sanity check” for the analysis: it confirms what we already know about string quartets.

In the final manipulation, they show that when small changes were made to the first violin’s part without telling the others, the MDF of the first violin actually went down. Now, this sounds counter-intuitive, as surely the one with the information should be driving the others? However, the MDF index could reflect the perturbation itself, and the tendency of the other players to stick together to the “original” version rather than go with the changed version. The aim is that of unity of sound, in the end.

I have used G-causality in a couple of analyses, and it works pretty well with musical data, and as authors emphasise, communication is necessarily bidirectional in these settings. Thus the MDF sounds like a good way to account for this. In terms of the increased information flow in the complex passages, I was wondering if it could be confounded by changes in the movement kinematics due to the complexity? If for example, people move more as they need to play more notes, there could be more variance in the movement, and this could influence the measure, even though it should in theory only look at predictability. It would be interesting to see some graphs of the movement measures.

These kinds of studies are very much needed, there aren’t too many of them around. This study is also very well conducted and clearly presented, a cool paper well worth reading! The phenomena of interpersonal coordination, communication and entrainment are very complex, and formulating theories on these requires a lot of empirical data, and now we have some more, with a neat analysis of influence and communication. So kudos for the infoMus group in Genoa for publishing this!
Leonardo Badino, Alessandro D’Ausilio, Donald Glowinski, Antonio Camurri, & Luciano Fadiga (2013). Sensorimotor communication in professional quartets Neuropsychologia DOI: 10.1016/j.neuropsychologia.2013.11.012

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