[The Influence of Light Tactile Contact on the Maintenance of Vertical Posture under the Conditions of Destabilization of the Visual Environment].

We studied the influence of a light contact of the index finger with a stationary surface of external environment on the maintenance of upright posture in healthy subjects "immersed" in unstable virtual visual environment. Under these conditions, the subjects saw the screen with a visual scene consisting of foreground and background. The foreground represented a window of a room with adjoining walls; and the background plan--an aqueduct with the adjacent terrain. The virtual visual environment was destabilized by setting inphase or antiphase links between the foreground and the oscillations of body. The analysis of the maintenance of upright posture was focused on the assessment of amplitude-frequency characteristics of two elementary variables calculated from trajectories of the center of pressure of feet (CoP) in mediolateral and anteroposterior directions: trajectory of the vertical projection of the center of gravity (CG variable) and differences between the trajectories of CoP and CG (CoP-CG variable). Both in normal posture and in posture with fingertip contact, the root mean square (RMS) values of the spectra of both variables were lowest in motionless visual environment with antiphase link of the foreground with body oscillations; highest, with inphase link and with eyes closed. In cases with fingertip contact, the intencity of body oscillations in both directions were considerably lower; the influence of different visual conditions on RMS values of the spectra of both variables decreased. This effect was more significant for CG variable. The frequency of body ascillations decreased as well. We observed the effect of tactile contacst on the frequency of the spectra of both variables. The median frequencies of the spectra of CoP-CG variable calculated from body oscillations in anteroposterior and mediolateral directions increased under the conditions of a tactile contact. On the contrary, the median frequencies of the spectra of CG variable increased only in body ascillations in mediolateral direction. Our results showed that a light tactile contact (providing no mechanical support) significantly improves the maintenance of vertical posture, including under conditions of destabilization of the virtual visual environment. This improvement is provided by multidirectional and independent effects on the amplitude-frequency characteristics of elementary variables (CG and CoP-CG).