Reduction in spread of excitation as predictor multi-channel spectral resolution

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Project Summary / Abstract Cochlear implant (CI) users may be unable to access all of the spectral information provided by their device because of channel interactions between electrodes. Current "focusing" may reduce channel interaction and thereby improve spectral resolution. Depending on patient-related factors (e.g., neuronal health, location of electrodes, etc.), individual CI users may or may not benefit from current focusing. The overall goals of this research are to improve CI users' functional spectral resolution via current focusing and to identify CI users that may benefit from focused stimulation. We hypothesize that if current focusing can reduce the spread of excitation, then channel interaction will be reduced and the spectral resolution will be increased, thereby CI performance in challenging listening conditions (e.g., speech in noise, music perception). If current focusing is applied to "current steered" virtual channels, the spectral resolution may be further increased. Ultimately, current shaping (steering and focusing) can be optimized for individual CI users, allowing for efficient transmission of the maximum amount of spectral cues for each patient. In Specific Aim 1, we will measure the spread of excitation (SOE) for single electrodes at multiple cochlear locations, with and without current focusing. In Specific Aim 2, we will measure perception of simple multi- channel stimuli, with and without current focusing. In Specific Aim 3, we will implement and evaluate experimental signal processing strategies with and without current focusing. Taken together, these experiments will provide important insights regarding the relevance of the SOE for perception of complex multi-channel stimuli, as well as guidance toward optimizing current shaping for individual CI patients in a clinical setting. The proposed research is significant because it aims to: a) improve CI performance in challenging listening conditions, b) develop current-shaping strategies for clinical processors, and c) create quick clinical tests to optimize current shaping for individual patients. The research is innovative in that it seeks to develop and implement new signal processing strategies to improve CI users' spectral resolution. The research approach combines objective measures (ECAPs), subjective descriptors, single- and multi-channel psychophysics, and evaluations of experimental signal processing to better understand who might benefit from current focusing, and under what circumstances.