Maintaining an Upright Posture with Different Sizes of the Object Providing Visual Feedback on Rigid and Compliant Supports

• Published in: Human physiology 2022-02, Vol.48 (1), p.1-12
• Main Authors: Kozhina, G. V., Levik, Yu. S., Popov, A. K., Smetanin, B. N.
• Format: Article
• Language: English
• Subjects: Balance; Biomedical and Life Sciences; Biomedicine; Feedback; Human Physiology; Life Sciences; Oscillations; Posture; Proprioception; Visual perception; Visual stimuli
• ISSN: 0362-1197; 1608-3164
• DOI: 10.1134/S0362119722010066

It was previously shown that the size of the visible object (sphere) providing visual feedback significantly influenced the maintenance of the vertical posture while standing on a rigid support. Thus, an increase in the size of a stationary sphere led to a decrease in body sway, and the same increase in the size of a moving sphere, on the contrary, increased oscillations. The frequency of oscillations of the center of gravity of the body (CoG) with a stationary sphere tended to increase with increasing size of the sphere, and with a moving one, it decreased. We tried to find out whether the relative contribution of the amplitude and frequency components of body oscillations to maintenance of a vertical posture will change on a compliant support. The subjects stood in stereo glasses in front of the screen, onto which a three-dimensional image of a sphere painted dark gray was projected. Three spheres covering visual fields of 4.5, 18, and 36 degrees, respectively, were used. The amplitude-frequency characteristics of two elementary variables were estimated: the trajectory of the projection of the body CoG on the support and the difference between the trajectories of the center of pressure (CoP) and the CoG (variable CoP–CoG). In the control, the sphere was motionless; under test conditions, the displacements of the sphere were in-phase or out-of-phase with the fluctuations of the CoG. The amplitude of the sphere’s oscillations was two times higher than the amplitude of oscillations of the CoG. On a compliant support, a more significant destabilization of the vertical posture was observed (about 1.5-fold with an immovable object and twofold with a movable one). The deterioration of standing on a compliant support occurred not only due to an increase in amplitudes, but also due to more significant (than with a rigid support) changes in the frequency characteristics of the CoP and CoP–CoG variables. Just as when standing on a rigid support, an increase in the size of the stationary sphere led to a decrease in the amplitude of the oscillations of the body, and an increase in the size of the movable sphere to its increase. On a compliant support with a stationary visual environment, the oscillations frequency of the CoG decreased with increasing size of the sphere. With a movable sphere and a compliant support, it practically did not change, and with a rigid it decreased. On the other hand, on a compliant support, the oscillation frequency of the variable CoP–Co