Coupling strength in tapping a 2:3 polyrhythm

The effects of tempo and role (fast vs. slow hand) on the reciprocal interaction (strength of coupling) between two hands tapping a 2:3 polyrhythm were examined from the perspective of nonlinear oscillator theory. A measure of the degree of harmonicity was developed, based on the relative contribution of the tapping frequency to the power spectrum of the limit cycle phase angle of each individual hand. On the assumption of fixed coefficients of the dissipative terms in the component oscillators, comparison of unimanual and bimanual performance with respect to this measure allowed for examination of the effects of the experimental conditions on the strength of the coupling. Five right-handed skilled drummers performed the 2:3 polyrhythm at several tempos and with both hand arrangements (i.e., either the preferred or the non-preferred hand tapped the faster cadence). The analysis revealed an inverse relation between tempo and coupling strength, and a larger influence of the fast hand on the slow hand than vice versa. No differences were observed between the two hand arrangements. The theoretical implications of these results were discussed in relation to similar and dissimilar findings in the literature.