Moore B C, Glasberg B R
J Acoust Soc Am. 1987 Jul;82(1):69-79. doi: 10.1121/1.395439.
When a signal is higher in frequency than a narrow-band masker, thresholds are lower when the masker envelope fluctuates than when it is constant. This article investigates the cues used to achieve the lower thresholds, and the factors that influence the amount of threshold reduction. In experiment I the masker was either a sinusoid (constant envelope) or a pair of equal-amplitude sinusoids (fluctuating envelope) centered at the same frequency as the single sinusoid (250, 1000, 3000, or 5275 Hz). The signal frequency was 1.8 times the masker frequency. At all center frequencies, thresholds were lower for the two-tone masker than for the sinusoidal masker, but the effect was smaller at the highest and lowest frequencies. The reduced effect at high frequencies is attributed to the loss of a cue related to phase locking in the auditory nerve. The reduced effect at low frequencies can be partly explained by reduced slopes of the growth-of-masking functions. In experiment II the masker was a sinusoid amplitude modulated at an 8-Hz rate. Masker and signal frequencies were the same as for the first experiment. Randomizing the modulation depth between the two halves of a forced-choice trial had no effect on thresholds, indicating that changes in modulation depth are not used as a cue for signal detection. Thresholds in the modulated masker were higher than would be predicted if they were determined only by the masker level at minima in the envelope, and the threshold reduction produced by modulating the master envelope was less at 250 Hz than at higher frequencies. Experiments III and IV reveal two factors that contribute to the reduced release from masking at low frequencies: The rate of increase of masked threshold with decreasing duration is greater at 250 Hz than at 1000 Hz; the amount of forward masking, relative to simultaneous masking, is greater at 250 Hz than at 1000 Hz. The results are discussed in terms of the relative importance of across-channel cues and within-channel cues.
当一个信号的频率高于窄带掩蔽声时，与掩蔽声包络恒定相比，掩蔽声包络波动时的阈值更低。本文研究了用于实现较低阈值的线索，以及影响阈值降低量的因素。在实验I中，掩蔽声要么是一个正弦波（恒定包络），要么是一对等幅正弦波（波动包络），其中心频率与单个正弦波相同（250、1000、3000或5275赫兹）。信号频率是掩蔽声频率的1.8倍。在所有中心频率下，双音掩蔽声的阈值都低于正弦掩蔽声，但在最高和最低频率下，这种效应较小。高频处效应降低归因于与听神经中相位锁定相关线索的丧失。低频处效应降低部分可由掩蔽增长函数斜率减小来解释。在实验II中，掩蔽声是一个以8赫兹速率进行幅度调制的正弦波。掩蔽声和信号频率与第一个实验相同。在强制选择试验的两半之间随机改变调制深度对阈值没有影响，这表明调制深度的变化未被用作信号检测的线索。调制掩蔽声中的阈值高于仅由包络最小值处的掩蔽声电平所预测的值，并且在250赫兹处，调制主包络产生的阈值降低比在较高频率处要小。实验III和IV揭示了导致低频处掩蔽释放减少的两个因素：在250赫兹处，掩蔽阈值随持续时间减小的增加速率比在1000赫兹处更大；相对于同时掩蔽，250赫兹处的前掩蔽量比1000赫兹处更大。根据跨通道线索和通道内线索的相对重要性对结果进行了讨论。
