Moore B C, Sek A
Department of Experimental Psychology, University of Cambridge, England.
J Acoust Soc Am. 1996 Oct;100(4 Pt 1):2320-31. doi: 10.1121/1.417941.
These experiments tested the hypothesis that detection of frequency modulation (FM) at very low rates depends mainly on temporal information (phase locking to the carrier) for carriers below about 5 kHz, whereas FM detection at higher rates (10 Hz and above) depends mainly on changes in the excitation pattern (a "place" mechanism). In experiment 1, thresholds for detecting FM were measured for a wide range of carrier frequencies (0.25-6 kHz) for modulation rates, fm, of 2, 5, 10, and 20 Hz. Thresholds were determined when FM only was present and when the carriers in both intervals of a forced-choice trial were amplitude modulated at the same rate as the FM with a modulation index of 0.333. The phase of the amplitude modulation (AM) relative to the FM was randomly selected on each trial, in order to disrupt cues for FM detection based on changes in the excitation pattern. For carrier frequencies up to 4 kHz, the deleterious effect of the added AM increased with increasing fm. For the 6-kHz carrier, the deleterious effect was independent of fm. In experiment 2, psychometric functions were measured for detecting combined FM and AM of a 1-kHz carrier, with fm = 2 Hz, as a function of the relative phase of the modulators. The modulation depths for AM and FM were chosen so that each would be equally detectable if presented alone. This was done both in quiet and in the presence of noise designed to mask either the lower or the upper side of the excitation pattern. In contrast to earlier results obtained with fm = 10 Hz [Moore and Sek, J. Acoust. Soc. Am. 96, 741-751 (1994)], only small effects of relative modulator phase were found. Experiment 3, was similar to experiment 2, except that all measurements were done in quiet, and carrier frequencies of 0.25, 1.0, and 6.0 kHz were used. There were no effects of relative modulator phase for the 0.25-kHz carrier, small effects for the 1-kHz carrier, and large effects for the 6-kHz carrier. The pattern of results is consistent with the hypothesis that both temporal and place mechanisms are involved in FM detection. The temporal mechanism dominates for carriers below about 4 kHz, and for very low modulation rates. The place mechanism dominates for high carrier frequencies, and for lower carrier frequencies when stimuli are frequency modulated at high rates.
对于低于约5千赫兹的载波，以非常低的速率检测频率调制（FM）主要依赖于时间信息（与载波的锁相），而对于较高速率（10赫兹及以上）的FM检测主要依赖于兴奋模式的变化（一种“位置”机制）。在实验1中，针对调制速率fm为2、5、10和20赫兹的多种载波频率（0.25 - 6千赫兹）测量了检测FM的阈值。当仅存在FM时以及在强制选择试验的两个间隔中的载波以与FM相同的速率进行幅度调制且调制指数为0.333时确定阈值。在每次试验中随机选择幅度调制（AM）相对于FM的相位，以破坏基于兴奋模式变化的FM检测线索。对于高达4千赫兹的载波频率，添加的AM的有害影响随fm的增加而增加。对于6千赫兹的载波，有害影响与fm无关。在实验2中，测量了检测1千赫兹载波的组合FM和AM（fm = 2赫兹）的心理测量函数，作为调制器相对相位的函数。选择AM和FM的调制深度，使得如果单独呈现，每个都同样可检测。这在安静环境中以及在旨在掩盖兴奋模式的低端或高端的噪声存在的情况下都进行了。与早期使用fm = 10赫兹获得的结果[Moore和Sek，《美国声学学会杂志》96，741 - 751（1994）]相反，仅发现了相对调制器相位的小影响。实验3与实验2类似，不同之处在于所有测量都在安静环境中进行，并且使用了0.25、1.0和6.0千赫兹的载波频率。对于0.25千赫兹的载波没有相对调制器相位的影响，对于1千赫兹的载波有小影响，对于6千赫兹的载波有大影响。结果模式与以下假设一致，即时间机制和位置机制都参与FM检测。时间机制在低于约4千赫兹的载波以及非常低的调制速率下占主导。位置机制在高载波频率下以及当以高速率对较低载波频率进行频率调制时占主导。
