Werner L A
Department of Speech and Hearing Sciences, University of Washington, Seattle 98105-6246, USA.
J Acoust Soc Am. 1999 Apr;105(4):2445-53. doi: 10.1121/1.426849.
Psychophysical forward-masked thresholds were estimated for 3- and 6-month-old infants and for adults. Listeners detected a repeated 1000-Hz probe, with 16-ms rise time, no steady-state duration, and 16-ms fall time. Unmasked thresholds were determined for one group of listeners who were trained to respond when they heard the probe but not at other times. In the masking conditions, each tone burst was preceded by a 100-ms broadband noise masker at 65 dB SPL. Listeners were trained to respond when they heard the probe and masker, but not when they heard the masker alone. The masker-probe interval, delta t, was either 5, 10, 25, or 200 ms. Four groups of subjects listened in the masked conditions, each at one value of delta t. Each listener attempted to complete a block of 32 trials including four probe levels chosen to span the range of expected thresholds. "Group" thresholds, based on average psychometric functions, as well as thresholds for individual listeners, were estimated. Both group and individual thresholds declined with delta t, as expected, for both infants and adults. Infants' masked thresholds were higher than those of adults, and comparison of masked to unmasked thresholds suggested that infants demonstrate more forward masking than adults, particularly at short delta t. Forward masking appeared to have greater effects on 3-month-olds' detection than on either 6-month-olds' or adults'. Compared to adults, 6-month-olds demonstrated more forward masking only for delta t of 5 ms. Thus, susceptibility to forward masking may be nearly mature by 6 months of age.
对3个月和6个月大的婴儿以及成年人进行了心理物理学前掩蔽阈值的估计。聆听者检测一个重复的1000赫兹探测音，其上升时间为16毫秒，无稳态持续时间，下降时间为16毫秒。为一组经过训练在听到探测音时做出反应而在其他时间不做反应的聆听者确定了非掩蔽阈值。在掩蔽条件下，每个音爆之前都有一个65分贝声压级的100毫秒宽带噪声掩蔽器。聆听者经过训练，在听到探测音和掩蔽器时做出反应，但在只听到掩蔽器时不做反应。掩蔽器 - 探测音间隔，即δt，分别为5、10、25或200毫秒。四组受试者在掩蔽条件下聆听，每组对应一个δt值。每个聆听者试图完成一组32次试验，包括选择的四个探测音水平，以涵盖预期阈值范围。基于平均心理测量函数的“组”阈值以及个体聆听者的阈值均被估计。正如预期的那样，对于婴儿和成年人，组阈值和个体阈值均随δt的增加而下降。婴儿的掩蔽阈值高于成年人，掩蔽阈值与非掩蔽阈值的比较表明，婴儿比成年人表现出更多的前掩蔽现象，特别是在短δt时。前掩蔽对3个月大婴儿的检测影响似乎比对6个月大婴儿或成年人的影响更大。与成年人相比，6个月大的婴儿仅在δt为5毫秒时表现出更多的前掩蔽现象。因此，到6个月大时，对前掩蔽的敏感性可能已接近成熟。
