Quantifying cooperation in choir singing: Respiratory and cardiac synchronisation

Cooperative tasks require coordinated joint actions among the participants, to the extent that a failure in an individual's action may have catastrophic consequences on the task of the group as a whole. One such activity is choir singing, where highly synchronised performance of the individual singers is a prerequisite to successful performance. The aim of this work is to provide a quantitative measure of the level of cooperation, established through the degrees of synchronisation between singers' physiological responses. To this end, we employ two new measures, the intrinsic phase synchrony and intrinsic coherence, which quantify synchronisation in respiration and heart rate variability (HRV) of: (i) five members of a choir and the conductor during a rehearsal and a real performance, and (ii) five members of the audience attending the performance. Both the proposed techniques successfully reveal degrees of synchronisation of singers' physiological signals which can be used as physically meaningful measures of the level of cooperation.