Research On Methods And Implementation Of Stimulus Synthesis In Cochlear Implants

Curing sensorineural heating loss is always the dream of many clinical doctors and scientists,and there is still a long way to go for neurons regenerative technique and gene-therapy methods to apply to clinical for sensorineural hearing loss treatment.So at present,as the unique and most effective rehabilitative measure for severe or totally sensorineural heating loss person,cochlear implant is accepted by more and more people of the world.Cochlear implants(CI) are medical devices that can restore partial hearing to a profoundly or totally deafened person via exciting the residual heating neurons directly in accordance with the principle of functional electrical stimulation.According to incomplete statistics, there are about 40 million deaf people in the word,and more than 100 thousand of them obtain and restore their heating through cochlear implantation.In spite of the high individual performance variability which due to various reasons among cochlear implant users,but average approximately,majority of them achieve their hearing to varying extent,some even could talk on the phone fluently in a quiet environment.Based on the previous researches,two new strategies of stimulus synthesis which called Wavelet Zero-crossing Stimulation(WZS) and Non-amplitude Modulation Strategy(NMS) are presented in this paper.On the basis of wavelet model of cochlea and the time-frequency encoding mode of auditory cortex on neural impulses,these two new strategies which generate stimulating pulsatile series at zero-crossings of processed speech signal in the domain of one-octave wavelet transform,could reduce or eliminate the interactions among channels and keep the temporal correlation and coherence of speech remained in stimulating pulsatile series,and these make the cochlear implant system based on WZS strategy could work more closely to the mode of cochlea.In this research,a piece of speech is selected and encoded with Compressed Analog(CA),Continuous Interleaved Sampling(CIS),WZS and NMS respectively by digital simulation software,also stimulating pulsatile series of each channel for above four strategies are synthesized and compared separately,results show that the spectrum of the synthesized speech signal via WZS encoding is more closer to that of the original speech signal and the WZS strategy is definitely efficient for cochlear implant system.Simultaneously,on the basis of computer simulation,hardware circuit of speech processor and decode module for WZS strategy is designed based on digital signal processor and complex programmable logic device.Finally,the hardware circuit is tested and analyzed through simulation software,the speech processor and decode module realize their capability well and based on the design we reach our expected goal.