Neff D L, Jesteadt W
Boys Town National Research Hospital, Omaha, Nebraska 68131, USA.
J Acoust Soc Am. 1996 Oct;100(4 Pt 1):2289-98. doi: 10.1121/1.417938.
This study examined the effects of multicomponent, random-frequency maskers and broadband-noise maskers on intensity discrimination at 1000 Hz. Maskers and signals were 200 ms, presented simultaneously. In the first set of conditions, thresholds were measured for the detection of a 1000-Hz tone in the presence of 40 or 60 dB SPL random-frequency or noise maskers, with extensive training of listeners with the random-frequency masker to assure stable effects of masker-frequency uncertainty. The random-frequency maskers had two, six, or ten components chosen at random from a large frequency range (300-3000 Hz, excluding a 160-Hz band around 1000 Hz). For these maskers, performance across the four listeners was very similar, showing large effects of masker-frequency uncertainty. For noise maskers, performance matched predictions for energy-based masking. In the second and third sets of conditions, intensity discrimination was measured at 1000 Hz for pedestals ranging from 40 to 80 dB SPL, first in isolation and then in the presence of the maskers. The pattern of results for intensity discrimination in quiet showed the expected near miss to Weber's Law, but poorer performance than typically observed. The addition of broadband-noise maskers had little effect on performance. However, random-frequency maskers degraded performance in nearly all conditions, with the size of the effect dependent on the level of the pedestal relative to the masker. Considering the pedestal as a tonal masker, the data were fitted with various models of combined masking. A simple power-law model provided excellent fits, with exponents ranging from 0.24 to 0.35 for the multicomponent maskers, but 1.0 (linear) for the noise. The results support models positing that the effects of individual maskers undergo nonlinear transformation before they are added, independent of the mechanisms which produce these effects. Because random-frequency maskers presumably produce informational (uncertainty-based) masking, the nonlinearity in this case appears central rather than peripheral.
本研究考察了多成分、随机频率掩蔽器和宽带噪声掩蔽器对1000Hz处强度辨别力的影响。掩蔽器和信号时长均为200ms，同时呈现。在第一组条件下，测量了在40或60dB SPL随机频率或噪声掩蔽器存在时检测1000Hz纯音的阈值，对听众进行了广泛的随机频率掩蔽器训练，以确保掩蔽器频率不确定性的稳定效应。随机频率掩蔽器有两个、六个或十个成分，从较大频率范围（300 - 3000Hz，不包括1000Hz左右160Hz的频段）中随机选取。对于这些掩蔽器，四名听众的表现非常相似，显示出掩蔽器频率不确定性的显著影响。对于噪声掩蔽器，表现符合基于能量掩蔽的预测。在第二组和第三组条件下，测量了1000Hz处强度辨别力，基座声压级范围为40至80dB SPL，首先是单独测量，然后是在掩蔽器存在的情况下测量。安静环境中强度辨别力的结果模式显示出对韦伯定律的预期接近但未达到，且表现比通常观察到的更差。添加宽带噪声掩蔽器对表现影响不大。然而，随机频率掩蔽器在几乎所有条件下都会降低表现，影响大小取决于基座相对于掩蔽器的声压级。将基座视为音调掩蔽器，数据用各种组合掩蔽模型进行拟合。一个简单的幂律模型拟合效果极佳，多成分掩蔽器的指数范围为0.24至0.35，但噪声的指数为1.0（线性）。结果支持这样的模型，即各个掩蔽器的效应在相加之前会经历非线性变换，这与产生这些效应的机制无关。因为随机频率掩蔽器可能产生信息性（基于不确定性）掩蔽，在这种情况下，非线性似乎是中枢性的而非外周性的。
