Although multichannel cochlear implants have achieved great success, there is a wide range of performance across patients. Understanding the cause of high variability of speech performance in cochlear implant users is still one of the biggest challenges in electric hearing. The present studies are aimed at understanding the factors that contribute to individual performance and at improving performance through modifications to the speech processor parameters. The hypothesis of this research is that speech perception in electric hearing is primarily based on a measure of similarity between the electrically-evoked peripheral neural discharge patterns and the central speech pattern templates. We further hypothesize that the central speech pattern templates can accommodate to some degree based on experience with new peripheral neural patterns. Two fundamental aspects of speech pattern recognition in electric hearing are addressed in this proposal.
The aim of the first experiment will be investigate how the peripheral neural patterns are affected by speech processor parameters. The match between the peripheral neural patterns and the central pattern templates will be inferred from speech performance. Recognition of vowels and consonants will be measured without any training period. The interactive efforts of three critical speech processor parameters: number of electrodes, the allocation of frequency regions to electrodes, and the stimulation mode and location of electrodes, will be investigated. The second experiment is aimed at understanding how the central speech pattern templates are altered by experience with new peripheral neural patterns of speech sounds. Experimental speech processors with significantly different peripheral neural patterns of speech sounds will be implemented in the subject's wearable speech processor. Speech performance as a function of the same speech processor parameters as those in Experiment 1 will be measured over time. Results from this study may indicate how far the central speech pattern templates can be altered and how long it takes. We believe that the results obtained from this proposal could improve speech performance of individual cochlear implant users through modifications to the speech processor parameters, lead to better designs of auditory prostheses, and improve understanding of speech pattern recognition in both acoustic and electric hearing.
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