Van Tasell D J, Crain T R
Department of Communication Disorders, University of Minnesota, Minneapolis.
Ear Hear. 1992 Apr;13(2):114-21. doi: 10.1097/00003446-199204000-00008.
Automatic frequency response (AFR) hearing aids usually reduce their low-frequency gain in the presence of noise; several investigators have reported improved recognition of high-frequency speech information in low-frequency band-limited noise with AFR versus non-AFR hearing aids. In this work, masking patterns (masked threshold for frequency-modulated probe tones as a function of probe frequency) were obtained for a narrowband low-frequency noise. Speech recognition threshold for a set of high-frequency loaded monosyllables also was obtained in the presence of the same noise. Aided speech and masking pattern data for one normal and two hearing-impaired subjects wearing a master hearing aid incorporating a commercially available AFR circuit showed modest AFR effects. Moreover, masking noise spectra measured in ear canals of subjects wearing the master hearing aid showed evidence of substantial hearing aid-generated distortion products in the AFR-off condition. Results obtained from the normal subject listening with a low-distortion laboratory simulation of an AFR hearing aid showed greater release from masking for the same low-frequency attenuation as provided by the hearing aid. Improvements of speech recognition in noise observed with AFR hearing aids may result from some combination of release from upward spread of masking and reduction of distortion products generated by the hearing aid in the non-AFR setting.
自动频率响应（AFR）助听器通常会在有噪声的情况下降低其低频增益；几位研究者报告称，与非AFR助听器相比，在低频带限噪声环境中，使用AFR助听器能提高对高频语音信息的识别能力。在这项研究中，针对窄带低频噪声获取了掩蔽模式（调频探测音的掩蔽阈值作为探测频率的函数）。在相同噪声环境下，还获取了一组高频加载单音节词的语音识别阈值。一名正常受试者和两名听力受损受试者佩戴了一款集成了市售AFR电路的主助听器，其辅助语音和掩蔽模式数据显示出适度的AFR效应。此外，在佩戴主助听器的受试者耳道中测量的掩蔽噪声频谱显示，在AFR关闭状态下存在大量助听器产生的失真产物。在低失真的AFR助听器实验室模拟环境中，正常受试者聆听所获得的结果表明，在与助听器提供的相同低频衰减情况下，能实现更大程度的掩蔽解脱。使用AFR助听器时观察到的噪声环境下语音识别能力的提高，可能是掩蔽向上扩展解脱与非AFR设置下助听器产生的失真产物减少这两种情况某种组合的结果。
