COUPLING DYNAMICS IN INTERLIMB COORDINATION

In 1:1 frequency locking, the interlimb phase difference PHI is an order parameter quantifying the spatial-temporal organization of 2 rhythmic subsystems. Dynamical modeling and experimental analyses indicate that an intentional parameter PHI(PSI), (intended coordination mode, PHI = 0-degrees or PHI = 180-degrees) and 2 control parameters omega(c) (coupled frequency) and DELTA(omega) (difference between uncoupled eigenfrequencies) affect PHI. An experiment was conducted on 1:1 frequency locking in which PHI(PSI), omega(c), and DELTAomega were manipulated using a paradigm in which a person swings hand-held pendulums. As DELTAomega deviated from 0, the observed PHI deviated from the PHI(PSI), indicating a displacement in the PHI attractor point. The displacements were exaggerated by increasing omega(c). The displacements were coordinated with a decrease in the stability of PHI and with higher harmonics in power spectrum of PHI. Implications of the results for modeling interlimb coordination are discussed.