Effects of the auditory prosthesis on postural stability.

To assess vestibular function in all 13 of the subjects, including two with external otitis who could not be stimulated calorically, postural stability was measured by means of computerized posturography. Testing was conducted both with eyes opened and closed and with the prosthesis off (no electrical stimulation) and with the prosthesis activated. All subjects demonstrated evidence of abnormal postural instability, particularly when visually deprived. Activation of the prostheses disrupted the subjects' postural stability, and upon visual deprivation, additional postural instability occurred. These findings suggest that the cochlear stimulators deliver a galvanic stimulus to the vestibular nerve or nuclei.