Auditory perception in vestibular neurectomy subjects

The auditory efferent nerve is a feedback pathway that originates in the br ainstem and projects to the inner ear. Although the anatomy and physiology of efferents have been rather thoroughly described, their functional roles in auditory perception are still not clear. Here, we report data in six hum an subjects who had undergone vestibular neurectomy, during which their eff erent nerves were: also presumably severed. The surgery had alleviated thes e subjects' vertigo but also resulted in mild to moderate hearing loss. We designed our experiments with a focus on the possible role of efferents in anti-masking. Consistent with previous studies, we found little effects of vestibular neurectomy on pure-tone detection and discrimination in quiet. H owever, we noted several new findings in all subjects tested. Efferent sect ion increased loudness sensation (one subject), reduced overshoot effect (f ive subjects), accentuated 'the midlevel hump' in forward masking (two subj ects), and worsened intensity discrimination in noise (four subjects). Poor er speech. in noise recognition was also observed in the surgery ear than t he non-surgery ear in three out of four subjects tested, bur this finding w as confounded by hearing loss. The present results suggest an active role o f efferents in auditory perception in noise. (C) 2000 Elsevier Science B.V. All rights reserved.