Project Summary/Abstract The objectives of our research are (1) to determine how conditions in the cochlea near the individual cochlear-implant electrodes affect specific psychophysical and electrophysiological measures of electrical hearing; (2) to determine the relationships of these specific measures to speech recognition with the cochlear prosthesis; and (3) to use this information to increase the benefit that cochlear implant patients receive from their prostheses. The data from these studies can be used in two ways to improve speech recognition in cochlear implant users. First, based on animal work that will correlate the pattern of pathology with functional measures, we will provide audiologists with simple, clinically-applicable measures they can use to assess individual stimulation sites in a patient's cochlea and guide selection of the best stimulation sites for an individual patient's speech processor MAP. Second, the data can help research scientists and surgeons determine the best anatomical targets for improving implant function through tissue-preservation and tissue- engineering strategies that make the impaired cochlea a better recipient of prosthetic stimulation. Our approach involves psychophysical and electrophysiological experiments in guinea pigs as well as psychophysical, electrophysiological and speech recognition studies in humans. We will measure psychophysical performance, such as perceptual integration of pulse trains or phase duration, and electrophysiological performance such as the rate at which evoked neural responses grow as a function of stimulus level. These measurements will be made at individual stimulation sites in guinea pigs and humans. In guinea pigs, we will determine the specific anatomical features in the hearing-impaired cochlea that are correlated with these measures. In humans we will determine the correlation of these same measures with speech recognition in quiet and in noisy backgrounds. We will then use these measures in humans to select the best stimulation sites to include in individual subjects' speech processor MAPs. This approach is supported by our previous studies showing that subjects usually perform better using a processor MAP that includes a subset of stimulation sites, carefully selected based on appropriate functional measures, than they do with a MAP that uses all available sites. The work proposed in this application will deepen our understanding of the mechanisms underlying variation in speech recognition performance across users of cochlear implants and serve as a guide for establishing and testing biological and clinical procedures that will improve performance in individual patients.