Fu Qian-Jie, Nogaki Geraldine
Department of Auditory Implants and Perception, House Ear Institute, 2100 West Third Street, Los Angeles, CA 90057, USA.
J Assoc Res Otolaryngol. 2005 Mar;6(1):19-27. doi: 10.1007/s10162-004-5024-3. Epub 2005 Apr 22.
The latest-generation cochlear implant devices provide many deaf patients with good speech recognition in quiet listening conditions. However, speech recognition deteriorates rapidly as the level of background noise increases. Previous studies have shown that, for cochlear implant users, the absence of fine spectro-temporal cues may contribute to poorer performance in noise, especially when the noise is dynamic (e.g., competing speaker or modulated noise). Here we report on sentence recognition by cochlear implant users and by normal-hearing subjects listening to an acoustic simulation of a cochlear implant, in the presence of steady or square-wave modulated speech-shaped noise. Implant users were tested using their everyday, clinically assigned speech processors. In the acoustic simulation, normal-hearing listeners were tested for different degrees of spectral resolution (16, eight, or four channels) and spectral smearing (carrier filter slopes of -24 or -6 dB/octave). For modulated noise, normal-hearing listeners experienced significant release from masking when the original, unprocessed speech was presented (which preserved the spectro-temporal fine structure), while cochlear implant users experienced no release from masking. As the spectral resolution was reduced, normal-hearing listeners' release from masking gradually diminished. Release from masking was further reduced as the degree of spectral smearing increased. Interestingly, the mean speech recognition thresholds of implant users were very close to those of normal-hearing subjects listening to four-channel spectrally smeared noise-band speech. Also, the best cochlear implant listeners performed like normal-hearing subjects listening to eight- to 16-channel spectrally smeared noise-band speech. These findings suggest that implant users' susceptibility to noise may be caused by the reduced spectral resolution and the high degree of spectral smearing associated with channel interaction. Efforts to improve the effective number of spectral channels as well as reduce channel interactions may improve implant performance in noise, especially for temporally modulated noise.
最新一代的人工耳蜗装置能让许多聋人患者在安静聆听环境下实现良好的语音识别。然而，随着背景噪声水平的增加，语音识别能力会迅速下降。先前的研究表明，对于人工耳蜗使用者而言，缺乏精细的频谱-时间线索可能导致其在噪声环境中的表现较差，尤其是当噪声为动态噪声时（例如，竞争说话声或调制噪声）。在此，我们报告了人工耳蜗使用者以及正常听力受试者在存在稳态或方波调制的语音形状噪声的情况下，对人工耳蜗声学模拟信号进行句子识别的情况。人工耳蜗使用者使用他们日常临床配备的语音处理器进行测试。在声学模拟中，正常听力的听众针对不同程度的频谱分辨率（16通道、8通道或4通道）和频谱模糊（载波滤波器斜率为-24或-6 dB/倍频程）进行了测试。对于调制噪声，当呈现原始的、未处理的语音时（保留了频谱-时间精细结构），正常听力的听众经历了显著的掩蔽解除，而人工耳蜗使用者则没有经历掩蔽解除。随着频谱分辨率的降低，正常听力听众的掩蔽解除逐渐减少。随着频谱模糊程度增加,掩蔽解除进一步降低。有趣的是，人工耳蜗使用者的平均语音识别阈值与聆听4通道频谱模糊噪声带语音的正常听力受试者的阈值非常接近。此外，人工耳蜗最佳聆听者的表现类似于聆听8至16通道频谱模糊噪声带语音的正常听力受试者。这些发现表明，人工耳蜗使用者对噪声的易感性可能是由与通道相互作用相关的频谱分辨率降低和高度频谱模糊所导致的。努力提高频谱通道的有效数量以及减少通道相互作用可能会改善人工耳蜗在噪声环境中的性能，特别是对于时间调制噪声。
