A stochastic analysis of superposed rhythmic synergies

Author(s): Turvey, M. T.

Journal/Book: Hum Movement Sci. 1997; 16: PO Box 211, 1000 AE Amsterdam, Netherlands. Elsevier Science BV. 33-80.

Abstract: Three experiments examined the bimanual coordination dynamics of persons producing circular motions with two hand-held pendulums. The task was modeled as a superposition of rhythmic synergies of motions in planes sagittal and transverse to the body. To examine the degree of interaction within the superposition three model potentials were compared by numerically fitting a stationary probability distribution estimated from the data to predictions from the Fokker-Planck equation. Experiment 1 examined isolated and superposed movements inphase and antiphase in each plane, and found differential stability between the circular patterns which were fit very well with a distribution assuming a higher-order coupling between the component movements. Simulations indicated that the method can qualitatively compare models, but will suffer quantitative inaccuracy for short trial durations and small noise strength. Experiment 2 replicated Experiment 1, and found that stability was greater for the slower of two coupled movement frequencies. Experiment 3 found that the higher-order coupling increased in strength relative to the lower-order couplings as movement frequency was increased, and antiphase relations in the higher-order coupling decreased in stability relative to inphase. The results are interpreted as a higher-order synergy formation which reduces the effective degrees of freedom the movement system must control.

Note: Article Collins DR, Univ Connecticut, Dept Psychol, Ctr Ecol Study Percept & Act, Box U-20, 406 Babbidge Rd, Storrs,CT 06268 USA

Keyword(s): relative phase; coordination; dynamics; variability; fluctuations; stochastic processes; phase transitions; PHASE-TRANSITIONS; INTERLIMB COORDINATION; DYNAMICS; MOVEMENTS; SYMMETRY; GAITS

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