Characterization Of Sound Source Orientation Information With Temporal Limits Encoder Strategy And Its Application In Bilateral Cochlear Implants

Cochlear implant(CI)is an electronic medical device that can help patients with severe to profound hearing impairment to partly regain hearing.Normal-hearing listeners mainly use interaural time differences(ITDs)and interaural level differences(ILDs)to localize sound sources in the horizontal plane.Listeners with bilateral CIs,however,are with poor sensitivity to ITDs.A very important reason is that most CI signal processing strategies are based on the temporal envelopes of the speech signal,whereas the temporal fine structure(TFS),which contains useful cues of ITDs to localize sound sources,is discarded.Recently,the Temporal Limits Encoder(TLE)strategy has been proposed as a new speech processing strategy.Compared with the Continuous Interleaved Sampling(CIS)strategy,it not only retains temporal envelope information,but also introduces slowly-varying fine structure information.In the case of unilateral cochlear implantation,simulated sound experiments have shown that the TLE strategy demonstrated improvements in speech-in-nose understanding and pitch perception.In this thesis,a series of subjective and objective experiments are designed to evaluate whether the slowly varying fine structure introduced by the TLE strategy can improve the spatial hearing of bilateral CI users.The objective envelope analysis shows that the bilateral TLE strategy contains ITDs information in the introduced slowvarying fine structure compared to the CIS strategy.The sound source localization experiment shows that the bilateral TLE strategy has better discrimination performance than the CIS strategy.The speech reception threshold(SRT)experiment shows that when the target sound and the interference sound come from different directions,the bilateral TLE strategy has a significant improvement compared with the CIS strategy.Put together,it can be seen that the bilateral TLE strategy can provide more information about ITDs for spatial hearing and then improve the spatial hearing perception ability of subject.