A STUDY ON COCHLEAR IMPLANT SYSTEM BASED ON A PHYSIOLOGICAL MODEL OF THE PERIPHERAL AUDITORY SYSTEM

这项研究的目的是对周围听觉模型进行逆向处理，并对人工耳蜗物进行多脉冲编码。我们提出了一种递归算法，该算法只从波形的正部分近似输入信号。在Meddis神经传导模型的基础上，通过求解神经传递物质的逆问题，实现了耳蜗非线性饱和特性的逆转换。并对Slaney的反向AGC(自动增益控制)在大输入时可能发生振荡的问题进行了重新研究。尽管在Meddis的模型中，对小信号的精度也很高，但对于大输入，它变得不稳定。由于它是一个线性系统，实现了声音系统从外耳到内耳的传递特性，但反向转换不足，提出了基于语音编码原理的高效多通道脉动算法，以实现对人工耳蜗电极刺激脉冲的高效转换。通过语音编码的方法，对输入的声音进行分析，得到近似过滤器，在此问题上搜索给定过滤器集合的最佳组合序列。获得使滤光器设置为标记的正/负的脉冲序列作为压缩语音信息，并将其与电极脉冲进行匹配。通过编解码检查编码的准确性时，发现能量较小的高频分量与低频分量相比，在分析过程中会丢失且运行时间较短。虽然高频增强和频谱平坦化处理相结合的效果是可以接受的，但在改善音质方面是不够的。尽管仍存在未解决的问题，但该系统作为一种高质量的语音编码用于人工耳蜗术的可能性得到了检验。

The purpose of this study is inverse processing of the peripheral auditory model and multi-pulse coding fro the cochlear implant. We proposed a recursive algorithm that approximates the input signal only from the positive part of the wave. Reverse conversion of the nonlinear saturation characteristic in cochlea was realized by solving a reverse problem about a nerve transfer substance on the basis of Meddis's nerve tranducion model. It also reexamined that an oscillation might occur in instability of the reversing AGC (automatic gain control) by Slaney for large inputs. Although the precision was high to small signals also in the Meddis's model, it became unstable to large inputs. Since it processed as a linear system, the transfer characteristic of the sound system which results in an inner ear from an outside ear was realized despite reverse conversion being inadequate.The efficient multi-channel pulsation algorithm based on the principle of the voice coding for efficient conversion to the cochlear implant electrode stimulation pulses was developed. By the voice coding method, analyzing an input sound and having obtained the approzimation filter, on this problem it searches for the optimum combination series about a given filter set. The pulse series of the positive/negative which makes a filter set a mark is obtained as compression voice information, and matches this with the electrode pulse. When accuracy of coding was checked by coding decoding, it was found that the high frequency components with small energy falls out and runs short in analysis process relatively compared with that of low frequency. Although the effect accepted when high frequency enhancement and spectrum flattening processing were incorporated, it was inadequate in respect of the tone-quality improvement. Although the unsolved problem had remained, the possibility of this system was checked as a quality voice coding for the cochlear implantation.