Visuomotor Adaptation in Healthy Humans in Standing Position under the Conditions of Destabilization of Virtual Visual Environment

Abstract—A study was made of the adaptive changes in the structure of body oscillations in the standing position in a three-dimensional virtual visual environment (VVE). The VVE was either immovable (IVVE) or mobile and unstable. The VVE was destabilized by introducing an in-phase relation between the VVE and body oscillations in the anteroposterior and lateral directions. In the course of the experiment, subjects performed 36 tests, each lasting 40 s, during which they stood still on a stabilograph, which recorded the trajectory of the center of pressure (CoP) of their body. The first three and last three tests were performed in IVVE conditions. The other 30 tests were divided into blocks of five tests each, in which the in-phase coupling (IPC) included with different gain factors: 1, 2, and 4. At a factor of 1, shifts in the VVE in the anteroposterior and lateral directions were equal in magnitude to the displacements of the subject’s body in the same direction. With factors of 2 and 4, the VVE displacements were, respectively, 2 and 4 times greater than the displacements of the body. Blocks of tests with different factors were introduced at random. A posture analysis was based on evaluating the amplitude-frequency characteristics of two elementary variables calculated from the CoP trajectories in the anteroposterior and lateral directions: the trajectory of the projection of the center of gravity on the support (variable CoG) and the difference between the trajectories of CoP and CoG (variable CoP–CoG). The results showed that body oscillations in both planes in the destabilized VVE were significantly greater than in the IVVE, but significantly decreased with test repetitions and especially to the end of the experiment. Improved maintenance of the vertical posture in a destabilized VVE was due to changes in both amplitude and frequency parameters of the variables CoG and CoP–CoG. The adaptive effects observed were assumed to be due to acquiring skills of leveling the influence of visual scene fluctuations on the posture and more efficiently using visual feedback from an immobile background of the VVE.