Visual field motion during a body pull affects compensatory standing and stepping responses
The aim of this study was to determine how visual motion evoked by an upper body perturbation during standing affects compensatory postural responses. This was investigated by rotating the visual field forwards or backwards about the ankle, time-locked to a forwards or backwards shoulder pull. Kinematic, kinetic and electromyographic responses were recorded to a range of pull forces over 160 trials in 12 healthy adults (mean = 31 years, S.D. =5.8). Stepping threshold forces and in-place postural responses were compared between conditions.
When the visual field moved in the same direction as the pull, so that the apparent velocity of the body was reduced (SLOW condition), the pull-force required to induce a step was less than when the visual field either rotated in the opposite direction (FAST) or was unaltered (NATURAL). For in-place responses, the body was displaced further in the direction of the pull in the SLOW condition. This was due to a reduction in the resistive force from lower leg muscles 130ms after the visual motion onset. In trials with no pull, the visual motion induced postural responses that were later (290ms) and had smaller amplitudes compared to when visual motion is paired with an unexpected perturbation of the body.
The results suggest that the apparent speed of the visual environment during a perturbation does influence whether a compensatory step is taken, not via a direct effect on the decision to step but by modulating the initial in-place response.
Publication titleJournal of Physiology
Department/SchoolSchool of Psychological Sciences
PublisherCambridge Univ Press
Place of publication40 West 20Th St, New York, USA, Ny, 10011-4211
Rights statementCopyright 2020 The Authors. This is the peer reviewed version of the following article: St George, RJ and Di Giulio, I and Day, BL, Visual field motion during a body pull affects compensatory standing and stepping responses, Journal of Physiology ISSN 0022-3751 (2020). This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article has been published in final form at: http://dx.doi.org/10.1113/JP275436