Furukawa S, Moore B C
Department of Experimental Psychology, University of Cambridge, England.
J Acoust Soc Am. 1996 Oct;100(4 Pt 1):2299-311. doi: 10.1121/1.417939.
This study investigated how well listeners combine information about frequency changes imposed on different carrier frequencies. The pattern of frequency change over time was either identical or different across carriers; this is referred to as "coherence." Psychometric functions were measured for the detection of frequency modulation (FM) imposed on two sinusoidal carriers, with frequencies 1100 and 2000 Hz. The modulation of each carrier was equally detectable, as determined in preliminary experiments. A continuous pink noise background was used to mask the outputs of auditory filters tuned between the two carrier frequencies. In experiment 1, the carriers were gated synchronously with l-s steady state duration and 50-ms raised-cosine ramps. One cycle of 5-Hz sinusoidal FM was used, the carrier having unmodulated "fringes" on either side of this. The FM on the two carriers was symmetrically located about the temporal center of the stimulus. The relative timing of the onset of FM (lag) between the two carriers was systematically varied. When the FM overlapped partially or completely in time across carriers, detectability for coherent FM was often better than for incoherent FM, especially for lag = 0, and was also often better than predicted on the assumption that information about the FM on the two carriers was extracted independently and combined optimally. When the FM did not overlap in time across the carriers, the detectability of the combined FM was generally equal to or lower than the value predicted on this assumption. In experiment 2, the long steady-state fringes before and after the modulation were removed, and the modulation always started at the same time for the two carriers. The modulation rate was either 2.5, 5, or 10 Hz. Again, performance for coherent FM was generally better than for incoherent FM. The effect of FM coherence was greater at the lowest modulation rate but did not vary markedly with the number of modulation cycles. The detectability of coherent FM was well above the value predicted on the assumption that information from the two carrier frequencies was processed independently and combined optimally. These results indicate the auditory system has higher sensitivity to FM when the FM is coherent across carriers. Possible models to account for the results are discussed.
本研究调查了听者整合施加于不同载波频率上的频率变化信息的能力。不同载波上随时间变化的频率模式要么相同，要么不同；这被称为“连贯性”。测量了对频率分别为1100赫兹和2000赫兹的两个正弦载波施加调频（FM）时的心理测量函数。如在初步实验中所确定的，每个载波的调制均可同等检测到。使用连续的粉红噪声背景来掩蔽调谐在两个载波频率之间的听觉滤波器的输出。在实验1中，载波与1秒的稳态持续时间和50毫秒的升余弦斜坡同步门控。使用了5赫兹正弦调频的一个周期，载波在其两侧具有未调制的“条纹”。两个载波上的调频关于刺激的时间中心对称定位。两个载波之间调频起始的相对时间（滞后）被系统地改变。当调频在不同载波上部分或完全在时间上重叠时，相干调频的可检测性通常优于非相干调频，特别是对于滞后 = 0的情况，并且通常也优于基于两个载波上的调频信息被独立提取并进行最优组合这一假设所预测的值。当调频在不同载波上在时间上不重叠时，组合调频的可检测性通常等于或低于基于该假设所预测的值。在实验2中，去除了调制前后的长稳态条纹，并且两个载波的调制总是同时开始。调制率为2.5、5或10赫兹。同样，相干调频的性能通常优于非相干调频。调频连贯性的影响在最低调制率时更大，但随调制周期数没有明显变化。相干调频的可检测性远高于基于两个载波频率的信息被独立处理并进行最优组合这一假设所预测的值。这些结果表明，当调频在不同载波上具有连贯性时，听觉系统对调频具有更高的敏感性。讨论了可能解释这些结果的模型。
