Hall J W, Grose J H, Moore B C
School of Medicine, Division of Otolaryngology, University of North Carolina, Chapel Hill.
J Speech Hear Res. 1993 Apr;36(2):410-23. doi: 10.1044/jshr.3602.410.
Experiments 1 and 2 investigated the effect of frequency selectivity on comodulation masking release (CMR) in normal-hearing subjects, examining conditions where frequency selectivity was relatively good (low masker level at both low [500-Hz] and high [2500-Hz] signal frequency, and high masker level at low signal frequency) and where frequency selectivity was somewhat degraded (high masker level and high signal frequency). The first experiment investigated CMR in conditions where a narrow modulated noise band was centered on the signal frequency, and a wider comodulated noise band was located below the band centered on the signal frequency. Signal frequencies were 500 and 2000 Hz. The masker level and the frequency separation between the on-signal and comodulated flanking band were varied. In addition to conditions where the flanking band and on-signal band were presented at the same spectrum level, conditions were included where the spectrum level of the flanking band was 10-dB higher than that of the on-signal band, in order to accentuate effects of reduced frequency selectivity. Results indicated that CMR was reduced at the 2000-Hz region when masker level was high, when the frequency separation between on-signal and flanking band was small, and when a 10-dB level disparity existed between the on-signal and flanking band. In the second experiment, CMR was investigated for narrow comodulated noise bands, presented either without any additional sound or in the presence of a random noise background. CMR increased slightly as the masker level increased, except at 2500 Hz when the noise background was present. The decrease in CMR at 2500 Hz with the high masker level and with a noise background present could be explained in terms of reduced frequency selectivity. In a third experiment, we compared performance for equal absolute bandwidth maskers at a low (500-Hz) and a high (2000-Hz) stimulus frequency. Results here suggested that detection in modulated noise may be reduced due to a reduction in the number of quasi-independent auditory filters contributing temporal envelope information. The effects found in the present study using normal-hearing listeners under conditions of degraded frequency selectivity may be useful in understanding part of the reduction of CMR that occurs in cochlear-impaired listeners having reduced frequency selectivity.
实验1和实验2研究了频率选择性对听力正常受试者的共调制掩蔽释放（CMR）的影响，考察了频率选择性相对较好的条件（在低频[500赫兹]和高频[2500赫兹]信号频率下掩蔽声强度均较低，以及在低频信号频率下掩蔽声强度较高）和频率选择性有所下降的条件（掩蔽声强度较高且信号频率较高）。第一个实验研究了在窄带调制噪声以信号频率为中心、宽带共调制噪声位于以信号频率为中心的频带下方的条件下的CMR。信号频率为500赫兹和2000赫兹。掩蔽声强度以及信号所在频带与共调制旁带之间的频率间隔有所变化。除了旁带和信号所在频带以相同频谱水平呈现的条件外，还包括旁带频谱水平比信号所在频带高10分贝的条件，以突出频率选择性降低的影响。结果表明，当掩蔽声强度较高、信号所在频带与旁带之间的频率间隔较小时，以及当信号所在频带与旁带之间存在10分贝的电平差异时，2000赫兹区域的CMR会降低。在第二个实验中，研究了窄带共调制噪声在无任何额外声音或存在随机噪声背景情况下的CMR。CMR随着掩蔽声强度的增加而略有增加，但在2500赫兹且存在噪声背景时除外。2500赫兹时在高掩蔽声强度且存在噪声背景情况下CMR的降低可以用频率选择性降低来解释。在第三个实验中，我们比较了在低（500赫兹）和高（2000赫兹）刺激频率下等绝对带宽掩蔽声的表现。此处的结果表明，由于贡献时间包络信息的准独立听觉滤波器数量减少，调制噪声中的检测可能会降低。本研究在频率选择性降低的条件下使用听力正常的受试者所发现的效应，可能有助于理解在频率选择性降低的耳蜗受损受试者中发生的CMR降低的部分原因。
