听觉脑干植入声码器模型的开发及验证

Establishment and verification of auditory brainstem implant vocoder model

目的·基于人工耳蜗(cochlear implant,CI)声码器及听觉脑干植入(auditory brainstem implant,ABI)电极阵列排布特征,开发ABI声码器并验证其可靠性。方法·通过MATLAB软件构建“n-of-m”编码策略的CI/ABI声码器。每一帧内仅选取能量最大的n个通道的包络,其中串扰系数(interaction coefficient,IC)(范围1~3)、通道数(范围5~22)、电极阵列拓扑模式(CI/ABI)为可调节参数,可合成仿真语音。招募正常听力受试者进行闭合式仿真音素的测听,并将音素识别准确率(元音20题/条件,辅音11题/条件)与参考文献中对应条件的CI及ABI植入者的音素准确率进行比较,明确声码器的IC值并验证其可靠性。结果·声码器可成功合成所有测试用仿真声。IC2、IC32个条件的仿真元音及辅音识别准确率与参考文献相应数据比较,差异均无统计学意义(P>0.05);IC2与参考文献中元/辅音准确率的差值较IC3与参考文献数据的差值更小(元音|d|:1.6%vs.20%;辅音|d|:8.4%vs.9.9%),确定本模型的最优IC为2。修改电极阵列拓扑模式为ABI,显示16通道ABI仿真音素识别准确率显著低于16通道CI。5~8通道间的ABI仿真元/辅音正确率比较,差异无统计学意义(P>0.05),与参考文献结论一致。结论·成功建立了基于“n-of-m”编码策略的CI/ABI声码器,并确定最佳IC。建立的ABI声码器经心理声学实验评估可靠性较高,可为ABI专属编码策略的模型验证提供合适的技术手段。

Objective·To develope an auditory brainstem implant(ABI)vocoder based on cochlear implant(CI)vocoder characteristics and ABI electrode array topology,and to verify its reliability.Methods·An"n-of-m"coding strategy CI/ABI vocoder was constructed based on MATLAB.Within each frame,only the envelopes of the n channels with the highest energy were selected.The interaction coefficient(IC)(range:1‒3),channel numbers(range:5‒22),and electrode array topology(CI/ABI)were adjustable parameters,allowing for the synthesis of simulated speech.Psychoacoustic evaluation was employed,recruiting normal hearing subjects to perform closed-set simulated phoneme perception.The phoneme recognition accuracy(20 vowel questions/condition,11 consonant questions/condition)was compared with the corresponding conditions of CI and ABI from reference literature to determine the IC value of the vocoder and verify its reliability.Results·The vocoder successfully synthesized all test stimuli.In the closed-set CI-simulated speech recognition,the simulated vowel and consonant recognition accuracy for IC2 and IC3 conditions showed no significant difference compared to the accuracy reported in the CI reference literature(P>0.05).The difference in vowel and consonant accuracy between IC2 and the literature was smaller than that between IC3 and the literature(vowel|d|=1.6%vs.20%,consonant|d|=8.4%vs.9.9%),thus determining the optimal interaction coefficient of this model as 2.Subsequently,when modifying the electrode array topology to ABI,it was found that the simulated phoneme recognition accuracy for a 16-channel ABI was significantly lower than that for the 16-channel CI group,consistent with the reported literature.The simulated vowel and consonant accuracy within the 5‒8 channel range for ABI showed no significant difference(P>0.05),also aligning with the trend reported in the literature.Conclusion·A CI/ABI vocoder based on"n-of-m"coding strategy is established and the optimal IC is determined.The established ABI encoder has been evaluated for high reliability through psychoacoustic experiments.It provides suitable technical means for validating ABI-specific coding strategies.