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

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Abstract
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.

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