Cochlear implants have improved considerably over the course of the past 20 years, however, there is still agreat deal of variability on all measures of post-implant performance. The general goal of the experimentsproposed is to identify new ways to use electrophysiological measures to better understand the sources ofthat variability. Previous research from our laboratory has focused on measuring the response of theauditory nerve to electrical stimulation. The proposed studies will expand that early work to include not onlymeasures of neural activity recorded from the auditory nerve but also cortically evoked responses recordedin the same individuals. These responses will then be compared with performance on a broad range oflistening tasks including speech and music perception.While much of the research proposed will be conducted with adult implant users, the results will be directlyapplicable to pediatric populations. Peripheral measures such as the electrically evoked compound actionpotential (ECAP) recorded using telemetry systems incorporated into commercial cochlear implants havebecome important tools for both initial programming and monitoring of young children. It is not only possibleto record the cortical responses we propose in young children but specific features of these responses havealready been shown to follow developmental trends in children and to be indicative of performance (Sharmaet al. 2002a; Ponton et al., 2000). The studies outlined in this proposal are important because they expandon previously published work to include assessment of cortical potentials evoked using a change in thepattern of ongoing electrical stimulation, a feature that simulates more closely the type of stimulation that istypical of everyday listening.Many of the proposed experiments focus on patients who use standard cochlear implants, however,experiments are also included that use these techniques in new populations of cochlear implant users suchas those patients who use the Hybrid cochlear implant system and patients who receive bilateral cochlearimplants. For each subject group, we have proposed experiments addressing the relationship betweenelectrophysiological measures and performance. We will also assess changes that occur over time withcontinued implant use in both pediatric as well as geriatric populations. We expect that, based on results ofthe studies proposed, we will be able to more fully characterize the differences we observe acrossindividuals and use that information to assist with clinical decision making, inform candidate selection andinfluence the ways the speech processor is programmed in order to maximize performance for an individualuser.
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