Moore B C, Huss M, Vickers D A, Glasberg B R, Alcántara J I
Department of Experimental Psychology, University of Cambridge, UK.
Br J Audiol. 2000 Aug;34(4):205-24. doi: 10.3109/03005364000000131.
Hearing impairment may sometimes be associated with complete loss of inner hair cells (IHCs) over a certain region of the basilar membrane. We call this a 'dead region'. Amplification (using a hearing aid) over a frequency range corresponding to a dead region may not be beneficial and may even impair speech intelligibility. However, diagnosis of dead regions is not easily done from the audiogram. This paper reports the design and evaluation of a method for detecting and delimiting dead regions. A noise, called 'threshold equalizing noise' (TEN), was spectrally shaped so that, for normally hearing subjects, it would give equal masked thresholds for pure tone signals at all frequencies within the range 250-10,000 Hz. Its level is specified as the level in a one-ERB (132 Hz) wide band centred at 1000 Hz. Measurements obtained from 22 normal-hearing subjects and TEN levels of 30, 50 and 70 dB/ERB confirmed that the signal level at masked threshold was approximately equal to the noise level/ERB and was almost independent of signal frequency. Masked thresholds were measured for 20 ears of 14 subjects with sensorineural hearing loss, using TEN levels of 30, 50 and 70 dB/ERB. Psychophysical tuning curves (PTCs) were measured for the same subjects. When there are surviving IHCs corresponding to a frequency region with elevated absolute thresholds, a signal in that frequency region is detected via IHCs with characteristic frequencies (CFs) close to that region. In such a case, threshold in the TEN is close to that for normal-hearing listeners, provided that the noise intensity is sufficient to produce significant masking. Also, the tip of the PTC lies close to the signal frequency. When a dead region is present, the signal is detected via IHCs with CFs different from that of the signal frequency. In such a case, threshold in the TEN is markedly higher than normal, and the tip of the PTC is shifted away from the signal frequency. Generally, there was a very good correspondence between the results obtained using the TEN and the PTCs. We conclude that the measurement of masked thresholds in TEN provides a quick and simple method for the diagnosis of dead regions.
听力障碍有时可能与基底膜特定区域内的内毛细胞（IHC）完全丧失有关。我们将此称为“死区”。在与死区对应的频率范围内进行放大（使用助听器）可能并无益处，甚至可能损害言语清晰度。然而，仅通过听力图并不容易诊断死区。本文报告了一种用于检测和界定死区的方法的设计与评估。一种名为“阈值均衡噪声”（TEN）的噪声经过频谱整形，以便对于听力正常的受试者，它能在250 - 10,000 Hz范围内的所有频率上为纯音信号提供相等的掩蔽阈值。其电平规定为以1000 Hz为中心的一个等效矩形带宽（132 Hz）内的电平。从22名听力正常的受试者获得的测量结果以及30、50和70 dB/ERB的TEN电平证实，掩蔽阈值处的信号电平大约等于噪声电平/ERB，并且几乎与信号频率无关。使用30、50和70 dB/ERB的TEN电平，对14名感音神经性听力损失受试者的20只耳朵测量了掩蔽阈值。对相同受试者测量了心理物理学调谐曲线（PTC）。当存在与绝对阈值升高的频率区域相对应的存活内毛细胞时，该频率区域内的信号通过特征频率（CF）接近该区域的内毛细胞被检测到。在这种情况下，只要噪声强度足以产生显著掩蔽，TEN中的阈值就接近听力正常的聆听者的阈值。此外，PTC的峰值接近信号频率。当存在死区时，信号通过CF与信号频率不同的内毛细胞被检测到。在这种情况下，TEN中的阈值明显高于正常水平，并且PTC的峰值偏离信号频率。一般来说，使用TEN和PTC获得的结果之间存在非常好的对应关系。我们得出结论，测量TEN中的掩蔽阈值为死区的诊断提供了一种快速且简单的方法。
