The proposed studies will identify the audiological, neurological, neurophysiological, perceptual, and genetic features of a new type of hearing impairment secondary to the neuropathy of the VIIIth Cranial Nerve. These patients have light-to-moderate impairment of pure tone thresholds, marked impairment of speech comprehension, absence of auditory brain stem potentials, but preserved measures of cochlea outer hair cell function (intact otoacoustic emissions). This project will quantify the disturbances of auditory perception (timing, frequency, and intensity) and compare the findings to patients with pure tone hearing deficits of cochlear origin. The electrophysiological methods will define auditory pathway activity and provide objective measures to localize the disorder with the VIIIth nerve. The patients will have neurological studies (clinical examinations, nerve conduction measures, electromyography, cranial nerve tests) to define the extent and distribution of the neuropathic disorder. A search for the genetic basis of the disorder will be made since a number of these patients have now been found to have a hereditary disturbance of peripheral nerve function. The possibility of a genetic identification for this disorder may lead to molecular methods of treatment for the disorder.
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