Erroneous Perception of Vertical Motion by Humans Seated in the Upright Position

The reliability of subjective response to vertical linear accelerations in the absence of vision has been examined in human subjects seated in the upright position. Helicopters and a vertical movement simulator were used to generate sinusoidal vertical movement of period 2-10 sec and acceleration amplitude 0.2-0.4 g. Subjective response was recorded as a continually variable assessment of vertical position. Without prior knowledge of the movement pattern, subjects were aware of movement but registered its form with a performance little better than chance. Light to moderate simulated “turbulence” did not significantly alter performance. Detailed consideration of end-organ orientation in the skull suggests the possibility that relative paucity of vestibular afferent information about vertical movement may account at least in part for the poor tracking performance observed in these experiments.