Cokely C G, Humes L E
Indiana University, Department of Speech and Hearing Sciences, Bloomington 47405.
J Acoust Soc Am. 1993 Nov;94(5):2553-9. doi: 10.1121/1.407367.
The present paper describes the results from two experiments which explored the temporal boundary between overlapping and nonoverlapping maskers and its effects on the additivity of masking. In the first experiment, detection thresholds for a short-duration 1000-Hz signal were measured in the presence of two equal-duration broadband maskers which varied in degree of temporal overlap. Following complete overlap of maskers, the temporal separation of masker onsets was systematically varied to create conditions ranging from partially overlapping simultaneous masking to combined forward and backward masking. The signal was always temporally centered between the onset of the first masker and the offset of the second masker. Nonlinear additivity of masking occurred for the majority of subjects when maskers and signal did not overlap, whereas linear additivity resulted for all subjects when the maskers and signal overlapped. In the second experiment, two separate forward maskers were used so that masker/masker overlap could be manipulated independent from masker/signal overlap. Maskers were changed gradually from temporally overlapping, or concurrent, forward maskers to sequential forward maskers. Results for all subjects showed nonlinear additivity for all combined-masker conditions. Together, these two experiments indicated that nonlinear masking additivity is observed when the signal does not overlap temporally with the maskers. However, when maskers and signal overlap temporally (and spectrally), linear additivity is observed.
本文描述了两项实验的结果，这两项实验探究了重叠掩蔽器和非重叠掩蔽器之间的时间界限及其对掩蔽相加性的影响。在第一个实验中，在存在两个等时长宽带掩蔽器的情况下，测量了短时长1000赫兹信号的检测阈值，这两个掩蔽器的时间重叠程度不同。在掩蔽器完全重叠之后，系统地改变掩蔽器起始的时间间隔，以创建从部分重叠的同时掩蔽到前向和后向掩蔽组合的条件。信号始终在时间上位于第一个掩蔽器起始和第二个掩蔽器结束之间的中心位置。当掩蔽器和信号不重叠时，大多数受试者出现了掩蔽的非线性相加性，而当掩蔽器和信号重叠时，所有受试者都出现了线性相加性。在第二个实验中，使用了两个单独的前向掩蔽器，以便可以独立于掩蔽器/信号重叠来控制掩蔽器/掩蔽器重叠。掩蔽器从时间上重叠的或同时的前向掩蔽器逐渐变为连续的前向掩蔽器。所有受试者在所有组合掩蔽器条件下的结果都显示出非线性相加性。这两项实验共同表明，当信号在时间上与掩蔽器不重叠时，会观察到非线性掩蔽相加性。然而，当掩蔽器和信号在时间上（以及频谱上）重叠时，则会观察到线性相加性。
