Diffusive, Synaptic, and Synergetic Coupling: An Evaluation Through In-Phase and Antiphase Rhythmic Movements

The in-phase and antiphase patterns of interlimb 1:1 frequency locking were contrasted with respect to models of coordination dynamics in biological movement systems that are based on diffusive coupling, synaptic coupling, and synergetic principles. Predictions were made from each model concerning the stable relative phase φ between the rhythmic units, its standard deviation SDφ and the self-chosen coupled frequency ω_c The experimental task involved human subjects oscillating two handheld pendulums either in-phase or antiphase. The eigenfrequencies of the two hand-pendulum systems were manipulated by varying the length and mass of each pendulum individually. Relative to an eigenfrequency difference of δωequal to zero, |Δ| > 0 displaced φ from φ = 0 and φ = π, and amplified SDφ. ω_c decreased with |Δω|. Both the displacement of φ and SDφ were greater in the antiphase mode. Additionally, the displacement of φ increased more sharply with |Δω| for antiphase than for in-phase coordination. In contrast, ω_c was identical for the two coordination modes. Of the models of interlimb coordination dynamics, the synergetic model was the most successful in addressing the pattern of dependencies of φ and SDφ. The specific forms of the functions relating ω_c and φ to Δωpose challenges for all three models, however.