Carlyon R P
MRC Institute of Hearing Research, University of Nottingham, U.K.
Hear Res. 1988 Jan;32(1):65-79. doi: 10.1016/0378-5955(88)90147-5.
Three experiments investigated the forward masking of brief sinusoids by bursts of noise for masker durations of between 5 and 320 ms and for masker-signal delays between 5 and 40 ms. Experiment 1 showed that, for a 2-kHz signal and a 5-ms delay, long-duration maskers produced much more masking than brief maskers of the same spectrum level. As masker-signal delay was increased, thresholds dropped more rapidly for long than for brief maskers, so that at a delay of 40 ms the difference between thresholds produced by long and by brief maskers was reduced. Experiment 2 showed that, for a 2-kHz signal, the transition from simultaneous masking to forward masking was accompanied by a large drop of about 23 dB in threshold. For a 250-Hz signal this large drop did not occur until masker-signal delay was increased from 10 to 20 ms. For shorter masker-signal delays, brief 250-Hz maskers produced thresholds higher than those produced by longer maskers. The results of Experiment 2 are consistent with the idea that ringing on the basilar membrane causes the responses to masker and signal to overlap for delay times up to 10 ms. Experiment 3 compared the recovery functions for 3 markers of different durations, where the masker levels were adjusted so that each produced equal masking of a 2-kHz signal at a delay of 5 ms. Brief intense maskers produced slower recovery than longer weaker ones, indicating that the recovery from a given amount of forward masking depends on how that masking developed. The implications of this finding for attempts to explain forward masking in terms of short-term adaptation are discussed.
三项实验研究了噪声脉冲对短暂正弦波的前掩蔽效应，掩蔽器持续时间在5至320毫秒之间，掩蔽器与信号的延迟在5至40毫秒之间。实验1表明，对于2千赫的信号和5毫秒的延迟，长时间的掩蔽器比具有相同频谱水平的短暂掩蔽器产生的掩蔽效应要大得多。随着掩蔽器与信号延迟的增加，长时间掩蔽器的阈值下降速度比短暂掩蔽器更快，因此在40毫秒的延迟时，长时间掩蔽器和短暂掩蔽器产生的阈值差异减小。实验2表明，对于2千赫的信号，从同时掩蔽到前掩蔽的转变伴随着阈值大幅下降约23分贝。对于250赫的信号，直到掩蔽器与信号延迟从10毫秒增加到20毫秒时，这种大幅下降才会出现。对于更短的掩蔽器与信号延迟，短暂的250赫掩蔽器产生的阈值高于更长掩蔽器产生的阈值。实验2的结果与基底膜上的振铃导致掩蔽器和信号的反应在延迟时间长达10毫秒时重叠的观点一致。实验3比较了不同持续时间的3种掩蔽器的恢复函数，其中调整了掩蔽器的水平，以便每种掩蔽器在5毫秒的延迟时对2千赫的信号产生相等的掩蔽。短暂强烈的掩蔽器比更长较弱的掩蔽器恢复得更慢，这表明从给定程度的前掩蔽中恢复取决于该掩蔽效应的形成方式。讨论了这一发现对试图用短期适应来解释前掩蔽的影响。
