Coupling of posture and gait: mode locking and parametric excitation |
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Authors: | Kay B A Warren W H |
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Institution: | (1) Department of Cognitive and Linguistic Sciences, Box 1978, Brown University, Providence, RI 02912, USA, US |
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Abstract: | We investigate the temporal coordination of human gait and posture and infer the nature of their coupling. Participants viewed
a sinusoidally oscillating visual display which induced medial-lateral postural sway during treadmill walking, while display
frequency was varied (0.075–1.025 Hz). First, postural responses exhibited the usual low-pass characteristic but with an additional
resonance peak near the preferred stride frequency, although shifted downward by 0.12 Hz; this provides evidence of a coupling
from gait to posture. Second, the step cycle adapted to mode lock with the visual driver and postural sway, as well as displaying
instances of intermittency (slipping in and out of phase) and quasiperiodicity (phase wandering); this provides evidence of
a coupling from posture to gait. We observed a spectrum of integer mode locks, including a large 1:1 trapping region about
the stride frequency and superharmonic entrainment (stride frequency > driver frequency) at lower driver frequencies. A coupled-oscillator
model that incorporates a novel parametric coupling from posture to the gait “stiffness” term reproduces these features of
the data, including the resonance peak shift. Biological coordination patterns may thus emerge naturally as properties of
a system of appropriately coupled oscillators.
Received: 23 June 1999 / Accepted in revised form: 10 January 2001 |
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