MRC Institute of Hearing Research, University Park, Nottingham NG7 2RD, United Kingdom.
J Acoust Soc Am. 2013 Apr;133(4):2288-300. doi: 10.1121/1.4793270.
At high frequencies, interaural time differences (ITDs) are conveyed by the sound envelope. Sensitivity to envelope ITDs depends crucially on the envelope shape. Reverberation degrades the envelope shape, reducing the modulation depth of the envelope and the slope of its flanks. Reverberation also reduces the envelope interaural coherence (i.e., the similarity of the envelopes at two ears). The current study investigates the extent to which these changes affect sensitivity to envelope ITDs. The first experiment measured ITD discrimination thresholds at low and high frequencies in a simulated room. The stimulus was either a low-frequency narrowband noise or the same noise transposed to a higher frequency. The results suggest that the effect of reverberation on ITD thresholds was multiplicative. Given that the threshold without reverberation was larger for the transposed than for the low-frequency stimulus, this meant that, in absolute terms, the thresholds for the transposed stimulus showed a much greater increase due to reverberation than those for the low-frequency stimulus. Three further experiments indicated that the effect of reverberation on the envelope ITD thresholds was due to the combined effect of the reduction in the envelope modulation depth and slopes, as well as the decrease in the envelope interaural coherence.
在高频时，两耳间时间差（ITD）通过声音包络传递。对包络 ITD 的敏感性取决于包络的形状。混响会降低包络的形状，降低包络的调制深度和边缘的斜率。混响还会降低包络的两耳相干性（即两个耳朵的包络之间的相似性）。本研究探讨了这些变化在多大程度上影响对包络 ITD 的敏感性。第一个实验在模拟房间中测量了低频和高频时的 ITD 辨别阈值。刺激物要么是低频窄带噪声，要么是将相同的噪声移到更高的频率。结果表明，混响对 ITD 阈值的影响是乘法的。鉴于无混响时的阈值对于移频刺激物比对低频刺激物大，这意味着，就绝对值而言，由于混响，移频刺激物的阈值增加幅度比低频刺激物大得多。另外三个实验表明，混响对包络 ITD 阈值的影响是由于包络调制深度和斜率的降低以及包络两耳相干性的降低的综合作用所致。
