An Experiment Platform For Evaluation Of Cochlear Implant Coding Strategies

Cochlear implants(CIs)are designed to help people with severe-to-profound hearing loss to restore hearing,and most CI users achieve good one-on-one speech communication in quiet.However,CI users often perform much worse than their normal-hearing peers in tasks such as spatial hearing,speech perception in noise,and music perception.Research on CI coding strategy can hopefully improve hearing of CI users,and thus is of great meanings.One effective way of evaluating the performance of CI coding strategies is through psychoacoustic experiments,which demand certain test platforms for implementation.Development of such test platforms can serve the research on CI coding strategy,and therefore help to promote the advancement of coding strategies and benefit CI users.First,a CI psychoacoustic test platform was developed in this thesis.A test software supporting tests including speech,pitch and lexical tone perception was developed based on psychoacoustic methods,and a CCi-Mobile research processor was used to implement new coding strategies.Vocoders were also incorporated to allow simulations on normal-hearing listeners.To solve the problem that electrical stimuli are not under direct control in conventional acoustic stimulation mode,this test platform was also designed to support direct precise electrical streaming to allow direct control on electrical stimuli.Then,the developed test platform was applied in two CI coding strategy evaluation cases for experiments in actual CI users.Case one was about an envelope-based single-channel noisereduction algorithm(eVoice,adding noise estimation and noise reduction on conventional envelope-based strategies)implemented in devices of Nurotron.In this study,the quantitative index of the eVoice noise reduction was measured,which proved its advantage in stable noise and shortage in unstable noise.This study provides guidance on whether to turn the noise reduction on for nearly 15 thousand Nurotron users,which is of significance from the perspective of audiology.Case two was about the evaluation of a new temporal-fine-structure enhancement strategy named the temporal limits encoder(TLE).In this case,the CCi-Mobile research interface was used in the evaluation of this new strategy in actual CI users.Performance of TLE on pitch perception was measured.Results indicated that TLE could improve pitch perception.This case is of great value in terms of both CI signal processing and psychoacoustics.The psychoacoustic test platform presented in this thesis can be used in tests including Mandarin speech perception and basic psychophysical tests such as pitch perception.Stimuli can be presented through acoustic stimuli or direct electrical streaming.It offers a software and hardware solution for CI psychoacoustic experiments,which can be used in performance evaluation of CI coding strategies.This work can help to promote the advancement of CI technologies,benefit CI users,and therefore has a positive social effect.