Abstract
To clarify the correlation between the directions of body sway, auto-and cross-correlation functions were computed. Two dimensional sways of the body center of gravity were recorded by stabilometer. The data were transmitted to a computer in the form of digital values after AD conversion sampled at intervals of 20 msec. Slow waves less than 0.15 Hz from the linear stabilogram were cut off with a digital filter. Auto-and cross-power spectra were calculated with fast Fourier transformation. Auto-and cross-correlation functions could be produced from these two power spectra.
In 30 normal subjects with eyes open, there was little correlation between the directions of body sway. With eyes closed, a strong correlation was obtained in only two subjects at a frequency of about 0.22 and 0.25 Hz. It seems that frontal and sagital body sway oscillates independently in each direction.
Ten out of 30 patients suffering from Meniere's disease showed a strong correlation in frontal and sagital directions with eyes closed. In two patients, the correlation was high even with eyes open. The frequency band was about 0.220.61 Hz, but the phase difference was relatively large.
In an investigation of 8 caloric-stimulated normal subjects, a strong correlation was observed when the amplitude of oscillations was large. The harmonic frequency band was about 0.180.65 Hz, and a phase difference was scarcely noticed. The human body acts like a pendulum when the vestibular system is disturbed.
