A STUDY ON A NEW COCHLEAR IMPLANT SYSTEM BASED ON A PERIPHERAL AUDITORY SYSTEM MODEL

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A numerical model of the peripheral auditory system was inverted. This is realized by solving an inverse problem of the Meddis's inner hair cell model using the amount of transduction with nonlinear characteristics in the cochlea. During this project term, three types of the auditory filters, that are Ohdaira's FIR filter bank, Patterson's Gamma-tone filter bank, and Sneff's IIR filter bank, are examined their amplitude and phase characteristics as an inverse filter. We found that the Ohdaira's filter outperformed over other two filters. we could demonstrate a good quality reproduced speech with the reverse processing of auditory firing pattern processed with the forward auditory model. The processing are programmed in MATLAB and Mathematica. The results are going to present at the TCPhS'99 conference this summer.We improved an algorithm for conversion from speech signal into electrode pulse of the multi-channel cochlear implant based on an efficient speech coding technology. This problem is analyzed as a compressed speech information where auditory filters are switched one by one. This process is reduced as to find an optimal combination of one by one stimulation sequence of bipolar pulse to a given set of filter. Coding quality was perceptually evaluated with resynthesis of coded speech. High frequency components, that are relatively lower than low frequency component, are not well encoded and heard almost missing. This result was presented at the international conference in Australia ICSLP'98 in Sydney. We could have an interesting discussion with Australian progressed cochlear implant researchers including a famous inventor of the multi-channel cochlear implant system G.M.Clark. They were very much impressed in our approach and asked me many questions and proposed further cooperation. During this project term, our cochlear implant study is internationally recognized and marked an important contribution to the history of cochlear implant study.