Effects of powerful sound stimulation on postural stability in humans

We examined the effects of powerful sound stimuli on postural stability in normal humans. Sound stimuli consisted of pure tone of 500 Hz, 105 dB HL for 5 sec duration, which were applied to the right ear. Each subject was studied under 4 different conditions: eyes open, eyes closed, head rotated 90 degree to the right and head rotated 90 degree to the left. Positive responses were observed in more than 85% of the subjects. Preponderance of response direction was indefinite under most conditions in subjects. Mono-phase postural responses were most elicited, but poly-phase responses were frequently observed in this experiment. In order to prove the vestibular-evoked responses, postural responses of patients with absent vestibular function and deaf patients have to be examined. Reproducibility and habituation of responses also will be examined in a future experiment.