Summers V, Leek M R
Army Audiology and Speech Center, Walter Reed Army Medical Center, Washington, DC 20307-5001, USA.
Hear Res. 1998 Apr;118(1-2):139-50. doi: 10.1016/s0378-5955(98)00030-6.
Tone detection and sentence recognition were measured for normally hearing and hearing-impaired listeners using maskers consisting of harmonic series with components summed in positive or negative Schroeder phase. Each task was carried out with the signal set at 60, 70, or 80 dB SPL. For listeners with normal hearing, positive Schroeder-phase complexes masked tones and sentences less than negative Schroeder-phase maskers. In the two experimental tasks, to achieve the same amount of masking, positive Schroeder-phase complexes had to be set as much as 12-15 dB higher than negative Schroeder-phase complexes. Large phase effects were observed on both tasks at all three test levels. The two maskers were more nearly equal in effectiveness in the presence of cochlear damage. The findings support an interpretation that involves differences in the shape of the basilar-membrane waveform generated by each masker and active cochlear processing which enhances the internal signal-to-masker ratio for signals presented in the positive Schroeder masker. This spectral enhancement appears to require nonlinear active gain that is characteristic of normal auditory processing at moderate presentation levels. The results of the sentence recognition task suggest that group differences observed in tone detection transfer fairly directly to speech perception under masking.
使用由谐波序列组成的掩蔽器，其分量以正或负施罗德相位相加，对听力正常和听力受损的听众进行音调检测和句子识别测量。每个任务在信号设置为60、70或80 dB SPL的情况下进行。对于听力正常的听众，正施罗德相位复合体对音调及句子的掩蔽小于负施罗德相位掩蔽器。在两项实验任务中，为达到相同的掩蔽量，正施罗德相位复合体的设置必须比负施罗德相位复合体高12 - 15 dB。在所有三个测试水平下的两项任务中均观察到较大的相位效应。在存在耳蜗损伤的情况下，两种掩蔽器的有效性更为接近。这些发现支持一种解释，该解释涉及每种掩蔽器产生的基底膜波形形状的差异以及主动耳蜗处理，这种处理增强了正施罗德掩蔽器中呈现信号的内部信号与掩蔽器比率。这种频谱增强似乎需要非线性主动增益，这是中等呈现水平下正常听觉处理的特征。句子识别任务的结果表明，在音调检测中观察到的组间差异相当直接地转移到了掩蔽条件下的语音感知中。
