Kluk Karolina, Moore Brian C J
Department of Experimental Psychology, University of Cambridge, Cambridge CB2 3EB, UK.
Hear Res. 2005 Feb;200(1-2):115-31. doi: 10.1016/j.heares.2004.09.003.
A dead region (DR) is a region of the cochlea where there are no functioning inner hair cells and/or neurons. DRs can be detected using the threshold-equalizing-noise (TEN) test, but psychophysical tuning curves (PTCs) are sometimes used to give a more precise estimate of the edge frequency of a DR; a shifted tip of the PTC indicates a DR. We show here that the shapes of PTCs for hearing-impaired subjects can be influenced by the detection of beats and simple difference tones (SDTs). As a result, PTCs can have tips at f(s), even when f(s) falls in a DR. PTCs were measured for subjects with mild to moderate low-frequency and severe high-frequency hearing loss using sinusoidal and narrowband noise maskers (80-, 160-, 320-Hz wide): (1) in quiet; (2) in the presence of additional lowpass filtered noise (LF noise) designed to mask SDTs; (3) in the presence of a pair of low-frequency tones designed to interfere with the detection of beats (MDI tones). In condition (1), the PTCs were often W-shaped, with a sharp tip at f(s). This occurred less for the wider noise bandwidths. For subjects with good low-frequency hearing, the LF noise often reduced or eliminated the tip at f(s), suggesting that this tip was partly caused by detection of SDTs. For the sinusoidal and 80-Hz wide noise maskers, the addition of the MDI tones reduced the masker level required for threshold for masker frequencies adjacent to f(s), for nearly all subjects, suggesting a strong influence of beat detection. To minimize the influence of beats, we recommend using noise maskers with a bandwidth of 160 or (preferably) 320 Hz. In cases of near-normal hearing at low frequencies, we recommend using an additional LF noise to mask SDTs.
死区（DR）是耳蜗中不存在功能正常的内毛细胞和/或神经元的区域。可以使用阈等效噪声（TEN）测试来检测死区，但有时会使用心理物理调谐曲线（PTC）来更精确地估计死区的边缘频率；PTC的尖端移位表明存在死区。我们在此表明，听力受损受试者的PTC形状可能会受到拍音和简单差频音（SDT）检测的影响。因此，即使f(s)落在死区内，PTC也可能在f(s)处有尖端。使用正弦和窄带噪声掩蔽器（80Hz、160Hz、320Hz宽）对轻度至中度低频和重度高频听力损失的受试者测量PTC：（1）在安静环境中；（2）在存在用于掩蔽SDT的额外低通滤波噪声（LF噪声）的情况下；（3）在存在一对用于干扰拍音检测的低频音（MDI音）的情况下。在条件（1）下，PTC通常呈W形，在f(s)处有尖锐的尖端。对于较宽的噪声带宽，这种情况较少发生。对于低频听力良好的受试者，LF噪声通常会降低或消除f(s)处的尖端，这表明该尖端部分是由SDT的检测引起的。对于正弦和80Hz宽的噪声掩蔽器，几乎所有受试者添加MDI音都会降低与f(s)相邻的掩蔽器频率阈值所需的掩蔽器电平，这表明拍音检测有很大影响。为了尽量减少拍音的影响，我们建议使用带宽为160Hz或（最好）320Hz的噪声掩蔽器。在低频听力接近正常的情况下，我们建议使用额外的LF噪声来掩蔽SDT。
