[Effect of weightlessness on the functions of perception and the reproduction of gravitational vertical in response to optokinetic stimulation].

In weightlessness spatial orientation largely depends on coordinated interaction of sensory systems involved in static orientation. The purpose of the present study was to quantify perception of spatial coordinates in response to optokinetic stimulation. Effects of weightlessness were simulated by dry water immersion hypokinesia. A custom-made optokinetic stimulator equipped with a device to measure perception of the gravitational vertical in response to optokinetic stimulation was used. A special platform with rubber bungee cords was employed to determine the role of the proprioceptive afferent input. It was demonstrated that during immersion day 1 the angle of erroneous perception of the vertical line consistently increased. By immersion day 3 the angle diminished suggesting adaptive developments. Additional proprioceptive inflow during immersion reduced significantly the error of perception. These findings indicate that the proprioceptive afferent input plays an important role in the mechanisms of spatial orientation at an early stage of exposure to weightlessness.