Recurrence dynamics and nonlinear system analysis of choral singing

Abstract This study investigates the interplay of cardiac, respiratory, and vocal activity during choral singing using recurrence quantification analysis (RQA) to capture underlying nonlinear dynamics. It was conducted to better understand how dynamic physiological and vocal subsystems interact and synchronize across different singing conditions. Our findings demonstrate significant differences in recurrence dynamics between resting and singing states and across different singing conditions. Singing altered recurrence dynamics, with increased synchronization and phase space integration compared to the resting state, especially for respiration. Subsystems exhibited distinct dynamic properties both within choir members and in interactions between them. Singing increased synchronization and reduced attractor fragmentation in the phase space, particularly for respiration. Subsystem dynamics varied by condition: singing in unison was characterized by more fragmented and irregular vocal dynamics, while singing in part led to more integrated and complex interactions. Bidirectional coupling between subsystems was observed, with the respiration and voice subsystems generally playing a leading role. The respiratory subsystem displayed stronger coupling with the vocal subsystem and often acted as the driving force in subsystem interactions. Periodic oscillatory patterns, particularly at frequencies aligning with the phrasing of the sung canon, were detected across all singing conditions, reflecting the dynamic nature of choir interactions. These findings underscore the complexity of choral singing, where subsystems interact dynamically in a context-dependent manner, with multilayered coupling mechanisms shaping overall system behavior. Our results suggest that the intricate, interwoven dynamics of choral singing can only be fully understood through detailed analysis of recurrence and coupling dynamics.