Validity of visual stabilization conditions used with computerized dynamic platform posturography

Temporal and spatial relationships between head motion and tilt of a visual surround were evaluated in conditions 3 and 6 of the sensory organization test (SOT) to determine the validity of visual stabilization during computerized dynamic platform posturography (CDP). Seven healthy subjects participated (mean age 42.4 years, SD = 19 years, range 25-72 years). Sagittal head translation and head pitch were evaluated separately with respect to displacement of the visual surround. Overall, the mean correlation between sagittal head motion and surround tilt was r = 0.68 for C3 and r = 0.93 for C6. The average phase (aggregate findings supported with trial-by-trial analysis), however, showed that sagittal head displacement leads motion of the visual surround ( + 452 ms for C3 and + 250 ms for C6). The mean correlation between head pitch and surround tilt was r = -0.30 for C3 and r = -0.72 for C6. Head pitch also leads visual surround motion (+567 ms for C3 and +539 ms for C6), but with greater variability than sagittal head translation. The results showed that visual stabilization was not consistently achieved during SOT conditions 3 and 6. The fundamental assumption that posture behaves as an inverted pendulum, with control of equilibrium originating in the lower extremities, does not appear to be applicable to the voluntary corrections of sway required during the SOT.