Edwards B W, Viemeister N F
Department of Psychology, University of Minnesota, Minneapolis 55455, USA.
J Acoust Soc Am. 1997 Feb;101(2):1010-8. doi: 10.1121/1.418024.
Contrary to level detection models, the thresholds for a brief-duration probe masked by a sinusoidal frequency modulation (FM) masker increases as the modulation index (beta) of FM increases [Zwicker, Acustica 31, 243-256 (1974)]. In this paper the reason for this phenomenon is investigated. In experiment 1, a 10-ms, 1-kHz probe was detected in the presence of an FM masker centered at 1 kHz and sinusoidally modulated at 16 Hz. Thresholds increased by over 15 dB with increasing beta, consistent with Zwicker's findings. In experiment 2, the instantaneous frequency changes of the masker used in experiment 1 were clipped and the resulting thresholds indicated that detection was determined primarily by the masker's total frequency excursion rather than by its instantaneous sweep rate. In experiment 3, the FM maskers from the first two experiments were passed through a roex filter centered at 1 kHz and the resulting envelope was used to amplitude modulate a 1-kHz tone, producing approximately the same effective envelope at 1 kHz as the FM maskers. Threshold functions for the amplitude modulated (AM) maskers were similar to those for their corresponding FM maskers. Thresholds increased by over 15 dB while the total energy of the AM masker decreased by over 10 dB, again contrary to standard level-detection models. The results from these experiments can be explained, at least qualitatively, by a model based on envelope shape discrimination: similarities between the envelopes of the masker alone and masker-plus-probe at the output of an auditory filter centered on the frequency of the probe are primarily responsible for the observed masking, particularly at large beta's.
与电平检测模型相反，被正弦频率调制（FM）掩蔽器掩蔽的短持续时间探测音的阈值会随着FM的调制指数（β）增加而升高[茨维克，《声学学报》31卷，243 - 256页（1974年）]。本文对这一现象的原因进行了研究。在实验1中，在以1kHz为中心、16Hz正弦调制的FM掩蔽器存在的情况下，检测一个10毫秒、1kHz的探测音。随着β增加，阈值升高超过15dB，这与茨维克的研究结果一致。在实验2中，对实验1中使用的掩蔽器的瞬时频率变化进行了截断，所得阈值表明检测主要由掩蔽器的总频率偏移决定，而非其瞬时扫描速率。在实验3中，将前两个实验中的FM掩蔽器通过一个以1kHz为中心的罗克斯滤波器，所得包络用于对一个1kHz的纯音进行幅度调制，在1kHz处产生与FM掩蔽器大致相同的有效包络。幅度调制（AM）掩蔽器的阈值函数与其相应的FM掩蔽器相似。阈值升高超过15dB，而AM掩蔽器的总能量降低超过10dB，这同样与标准电平检测模型相悖。这些实验的结果至少在定性上可以通过一个基于包络形状辨别能力的模型来解释：单独的掩蔽器以及在以探测音频率为中心的听觉滤波器输出端的掩蔽器加探测音的包络之间的相似性，是观察到的掩蔽现象的主要原因，尤其是在β较大时。
