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

建立了外周听觉系统的数值模型。这是通过利用耳蜗中具有非线性特征的转导量来求解Meddis内毛细胞模型的逆问题来实现的。在本项目期间，三种类型的听觉滤波器，即Ohdaira的FIR滤波器组，Patterson的Gamma-tone滤波器组和Sneff的IIR滤波器组，作为逆滤波器检查了它们的幅度和相位特性。我们发现Ohdaira的过滤器比其他两种过滤器性能更好。用正向听觉模型对听觉发射模式进行反向处理，可以得到高质量的语音再现。在MATLAB和Mathematica中编写了处理程序。研究结果将在今年夏天的TCPhS'99会议上公布。基于高效的语音编码技术，改进了多通道人工耳蜗语音信号到电极脉冲的转换算法。将此问题作为一个压缩的语音信息进行分析，其中逐个切换听觉滤波器。将这一过程简化为找到双极脉冲逐个刺激序列对给定滤波器的最优组合。用编码语音的再合成对编码质量进行感知评价。相对于低频分量，高频分量编码不好，几乎听不见。这一结果在澳大利亚悉尼举行的国际会议ICSLP'98上发表。我们可以与澳大利亚先进的人工耳蜗研究人员进行有趣的讨论，其中包括著名的多通道人工耳蜗系统的发明者g.m.k lark。他们对我们的做法印象非常深刻，向我提出了许多问题，并提出了进一步的合作。在这个项目期间，我们的人工耳蜗研究得到了国际上的认可，对人工耳蜗研究的历史做出了重要贡献。

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.