ASA 127th Meeting M.I.T. 1994 June 6-10

1pPP6. Human hearing without efferent input to the cochlea.

Bertram Scharf

Dept. of Psychol., Northeastern Univ., Boston, MA 02115

The measurement of hearing without efferent input is possible in human patients whose vestibular nerve has been sectioned, to relieve severe vertigo usually caused by Meniere's disease. The olivocochlear bundle, which runs in the inferior vestibular nerve, is also sectioned. Psychoacoustic measures have been made in over a dozen such patients, whose hearing levels range from normal to 40 or 50 dB. Most measurements were made only after the operation, but many were also made before. Thresholds measured before and after the operation revealed no change in the ability to detect tones either in the quiet or in noise, except when selective frequency focusing was involved. Comparisons between operated and normal ears showed a similar pattern. Other psychoacoustic tests, including measurements of intensity, frequency, and gap discrimination, of loudness functions and loudness adaptation, of lateralization, of the auditory filter (by notched noise), of overshoot, of TTS, showed either normal auditory functions or only the changes usually associated with sensorineural impairment. Besides the laboratory tests, most patients' reports indicate no change in hearing subsequent to the vestibular neurectomy. Apparently, the one change---in selective listening---has little effect on such common auditory functions as speech perception. [Research supported by NIH.]