Grimault Nicolas, Bacon Sid P, Micheyl Christophe
Department of Speech and Hearing Science, Arizona State University, Tempe 85287-1908, USA.
J Acoust Soc Am. 2002 Mar;111(3):1340-8. doi: 10.1121/1.1452740.
In this study, auditory stream segregation based on differences in the rate of envelope fluctuations--in the absence of spectral and temporal fine structure cues--was tested. The temporal sequences to segregate were composed of fully amplitude-modulated (AM) bursts of broadband noises A and B. All sequences were built by the reiteration of a ABA triplet where A modulation rate was fixed at 100 Hz and B modulation rate was variable. The first experiment was devoted to measuring the threshold difference in AM rate leading subjects to perceive the sequence as two streams as opposed to just one. The results of this first experiment revealed that subjects generally perceived the sequences as a single perceptual stream when the difference in AM rate between the A and B noises was smaller than 0.75 oct, and as two streams when the difference was larger than about 1.00 oct. These streaming thresholds were found to be substantially larger than, and not related to, the subjects' modulation-rate discrimination thresholds. The results of a second experiment demonstrated that AM-rate-based streaming was adversely affected by decreases in AM depth, but that segregation remained possible as long as the AM of either the A or B noises was above the subject's AM-detection threshold. The results of a third experiment indicated that AM-rate-based streaming effects were still observed when the modulations applied to the A and B noises were set individually, either at a constant level in dB above AM-detection threshold, or at levels at which they were of the same perceived strength. This finding suggests that AM-rate-based streaming is not necessarily mediated by perceived differences in AM depth. Altogether, the results of this study indicate that sequential sounds can be segregated on the sole basis of differences in the rate of their temporal fluctuations in the absence of other temporal or spectral cues.
在本研究中，我们测试了在没有频谱和时间精细结构线索的情况下，基于包络波动速率差异的听觉流分离。用于分离的时间序列由宽带噪声A和B的全幅度调制（AM）脉冲串组成。所有序列均由ABA三元组的重复构建而成，其中A的调制速率固定为100Hz，B的调制速率可变。第一个实验致力于测量导致受试者将序列感知为两个流而非一个流的AM速率阈值差异。第一个实验的结果表明，当A和B噪声之间的AM速率差异小于0.75倍频程时，受试者通常将序列感知为单个感知流；当差异大于约1.00倍频程时，则感知为两个流。发现这些流分离阈值远大于受试者的调制速率辨别阈值，且与之无关。第二个实验的结果表明，基于AM速率的流分离受到AM深度降低的不利影响，但只要A或B噪声的AM高于受试者的AM检测阈值，分离仍然是可能的。第三个实验的结果表明，当分别对A和B噪声施加调制时，无论是在高于AM检测阈值的恒定分贝水平，还是在它们具有相同感知强度的水平，基于AM速率的流分离效应仍然可以观察到。这一发现表明，基于AM速率的流分离不一定由AM深度的感知差异介导。总之，本研究结果表明，在没有其他时间或频谱线索的情况下，连续声音可以仅基于其时间波动速率的差异进行分离。
