Encoding of speech sounds at auditory brainstem level in good and poor hearing aid performers

Abstract Introduction: Hearing aids are prescribed to alleviate loss of audibility. It has been reported that about 31% of hearing aid users reject their own hearing aid because of annoyance towards background noise. The reason for dissatisfaction can be located anywhere from the hearing aid microphone till the integrity of neurons along the auditory pathway. Objectives: To measure spectra from the output of hearing aid at the ear canal level and frequency following response recorded at the auditory brainstem from individuals with hearing impairment. Methods: A total of sixty participants having moderate sensorineural hearing impairment with age range from 15 to 65 years were involved. Each participant was classified as either Good or Poor Hearing aid Performers based on acceptable noise level measure. Stimuli /da/ and /si/ were presented through loudspeaker at 65 dB SPL. At the ear canal, the spectra were measured in the unaided and aided conditions. At auditory brainstem, frequency following response were recorded to the same stimuli from the participants. Results: Spectrum measured in each condition at ear canal was same in good hearing aid performers and poor hearing aid performers. At brainstem level, better F0 encoding; F0 and F1 energies were significantly higher in good hearing aid performers than in poor hearing aid performers. Though the hearing aid spectra were almost same between good hearing aid performers and poor hearing aid performers, subtle physiological variations exist at the auditory brainstem. Conclusion: The result of the present study suggests that neural encoding of speech sound at the brainstem level might be mediated distinctly in good hearing aid performers from that of poor hearing aid performers. Thus, it can be inferred that subtle physiological changes are evident at the auditory brainstem in a person who is willing to accept noise from those who are not willing to accept noise.

【摘要引言】助听器被用于改善可听度损失。据报道，约31%的助听器使用者因无法耐受背景噪声而弃用助听器。使用者的不满原因可能涉及从助听器麦克风到听觉通路上神经元完整性的任一环节。

【研究目的】测量听力受损个体在耳道水平的助听器输出频谱，以及其听觉脑干记录的频率跟随反应（frequency following response）。

【研究方法】本研究共纳入60名年龄介于15至65岁的中度感音神经性听力损失参与者。依据可接受噪声水平测试结果，将每位参与者划分为助听器表现良好者（Good Hearing Aid Performers）与助听器表现不佳者（Poor Hearing Aid Performers）。通过扬声器以65 dB声压级（dB SPL）呈现刺激声/da/与/si/。在耳道层面，分别在未助听与助听状态下测量频谱；在听觉脑干层面，记录参与者对上述相同刺激声的频率跟随反应。

【研究结果】在各测试条件下，两组参与者耳道处测得的频谱并无显著差异。在脑干层面，助听器表现良好者的F0编码效果更优，其F0与F1能量显著高于表现不佳者。尽管两组的助听器输出频谱几乎一致，但听觉脑干存在细微的生理差异。

【研究结论】本研究结果表明，脑干层面的语音神经编码在助听器表现良好者与不佳者之间存在显著差异。由此可推断，与不愿耐受背景噪声的使用者相比，愿意耐受背景噪声的使用者其听觉脑干存在可观测的细微生理变化。