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

5aPP19. Effects of vestibular neurectomy on intensity discrimination and speech perception in noise.

House Ear Inst., 2100 West Third St., Los Angeles, CA 90057

Olivocochlear efferents are assumed to be severed during vestibular neurectomy in subjects with severe vertigo. Effects of vestibular neurectomy on pure-tone intensity discrimination and speech perception in noise were examined in six subjects by comparing performance between the surgery ear and the nonsurgery ear, and when available, between the pre- and post-operative conditions. Five of the six subjects had normal or near normal pure-tone average thresholds (<30 dB HL). Broadband white noise was used as in intensity discrimination, and speech spectral-shaped noise was used in speech reception threshold measurements. Both types of noise were presented binaurally at several different levels, whereas the tone or speech was presented monaurally and its level was varied adaptively according to the subject's response. Preliminary results show that (1) loudness dynamic range is not affected by the surgery, (2) intensity and speech perception in noise significantly worsen after the surgery in some subjects but not others. The variability of the results may be due to the fact that not all efferents are severed in every subject during vestibular neurectomy. An objective measure of the efferent nerve survival after vestibular neurectomy in these subjects is needed to further understand perceptual function of the cochlear efferent pathway. [Work supported by NIH-BRSG.]