Background: It has been shown that humans adapt their postural sway to oscillatory, visually simulated self-motion. However, little is still known about the way individual body segments contribute to this adjustment of body sway and how this contribution varies with different environmental conditions.
Research question: How do the centre of pressure (COP) and individual body segments phase-lock to a sinusoidal visual drive depending on the frequency of stimulation?
Methods: In this study, we introduce phase coupling as a method for assessing full body motion in response to visual stimuli presented in virtual reality (VR). 12 participants (mean age: 31 ± 9 years) stood inside a virtual tunnel which oscillated sinusoidally in the anterior-posterior direction at a frequency of 0.2 Hz, 0.8 Hz or 1.2 Hz. Primary outcome measures were the trajectories of their COP as well as of 25 body segments obtained by a motion tracking system.
Results: Subjects significantly coupled the phase of their COP and body segments to the visual drive. Our analysis yielded significant phase coupling of the COP to the stimulus for all tested frequencies. The phase coupling of body segments revealed a shift in postural response as a function of frequency. At the low frequency of 0.2 Hz, we found strong and significant phase coupling homogeneously distributed across the body. At the higher frequencies of 0.8 Hz and 1.2 Hz, however, overall phase coupling became weaker and was centred around the lower torso and hip segments.
Significance: Information on how the visual percept of self-motion affects balance control is crucial for understanding visuomotor processing in health and disease. Our setup and methods constitute a reliable tool for assessing perturbed balance control, which can be utilized in future clinical trials.
Keywords: Body sway; COP; Motion tracking; Phase coupling; Postural response; Visuomotor control.
Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.