Influence of Fixed Point Marks on Maintaining a Vertical Posture when Observing a Virtual Three-Dimensional Object Linked to Body Oscillations

Abstract—

The influence of additional visual information on the process of maintaining a vertical posture on a compliant support was studied. The subjects stood in stereo glasses and a mask that limited the field of view in a darkened room in front of a screen on which a three-dimensional image of a dark gray sphere was projected. The virtual sphere covered a field of view of approximately 36°. The presentation of the sphere was combined with the introduction of additional fixed objects (dots with an area of 1 cm²). The latter, in the amount of one or four, could be present in different places, but within the area covered by the sphere. In the control trials, the sphere was motionless. In test trials, the position of the sphere depended on body oscillations in the anteroposterior and lateral directions in such a way that body shifts caused the sphere to move in the same (in-phase connection, IP) or opposite directions (antiphase connection, AP). The contribution of visual control to posture maintenance was assessed by changes in the amplitude—frequency characteristics of elementary variables calculated from the trajectory of the sole center of pressure (CP). These variables were the vertical projection of the body’s center of gravity (CG) and the difference between the CP and the vertical projection of the center of gravity (CP–CG). An analysis of the CG and CP–CG variables revealed a clear dependence of their spectra on the direction of the connection between the shifts of the body and the sphere, as well as the influence of the presence of fixed points on this dependence. Thus, in test trials, in standing position with open eyes and in the absence of additional fixed points, the oscillations in the sagittal plane increased significantly compared to the control. In particular, there was an approximately 2.5-fold increase in the root-mean-square value of the amplitude spectra (RMS) under IP conditions and a 2-fold increase under AP conditions, while the RMS values of the spectra were also significantly higher than when standing with closed eyes. When one fixed point was added in the center of the screen as a fixed reference point, the oscillations practically did not change. When four points symmetrically located at a distance of 8.75 cm from the center of the screen were added, the RMS spectra of both variables decreased by 20–25%. With an increase in the distance between the points up to 35 cm, a further 30–35% decrease in body oscillations was observed. At a distance of 70 cm between the points (equal to the sphere diameter), the RMS of the spectra decreased by 45–50%. Under these conditions, the magnitude of body oscillations became approximately the same as with closed eyes. Thus, it is shown that under conditions of instability of the visual environment, the presence of stationary objects of small size significantly affects posture maintenance, but the quality of standing still remains lower than in a stationary visual environment.