Moore B C, Jorasz U
Department of Experimental Psychology, University of Cambridge, England.
J Acoust Soc Am. 1996 Oct;100(4 Pt 1):2373-81. doi: 10.1121/1.417947.
The discrimination of the depth of amplitude modulation (AM) of a target carrier can be adversely affected by the presence of other modulated carriers (flankers), an effect called modulation discrimination interference (MDI). Conversely, when the task is to detect a sinusoidal signal added to a modulated carrier of the same frequency, the presence of comodulated flankers (with the same modulation as the target carrier) can improve performance (comodulation masking release: CMR). This paper examines how CMR and MDI are influenced by the number and placement of the flankers. Flankers were spaced at 2-ERB intervals from the target, and their number was manipulated by adding flankers that were more remote from the target. Narrow-band noise (centered at 10 Hz) was used as the modulator for all carriers. In experiment 1, the MDI task required detection of a decrease in modulation depth (m) of the target from a reference value of 0.7. Unmodulated flankers did not affect thresholds. Modulated flankers (m = 0.15) produced MDI, which increased as more flankers were added. MDI was generally slightly greater for comodulated than for noncomodulated flankers. The CMR task required detection of a sinusoidal signal added (in 90 degrees phase) to the target carrier (m = 0.7). Unmodulated flankers or flankers that were noncomodulated with the target had no effect on threshold. Comodulated flankers (m = 0.7) gave CMR, which generally increased as more flankers were added. This effect was greater for flankers below the target frequency than for flankers above. Experiment 2 examined MDI using similar stimuli to experiment 1, except that the task was to detect an increase in m from a reference value of 0.1. Even unmodulated flankers elevated thresholds, and this effect increased as more flankers were added, especially on the high-frequency side of the target. Modulated flankers (m = 0.2) produced additional increases in threshold, and modulation thresholds generally increased as more flankers were added. However, the amount of MDI (the difference between thresholds with modulated and unmodulated flankers) did not vary systematically with the number of flankers and did not show consistent differences between comodulated and noncomodulated flankers. The results are interpreted in terms of the mechanisms underlying MDI and CMR, and especially perceptual grouping processes.
目标载波幅度调制（AM）深度的辨别可能会受到其他调制载波（侧翼信号）的不利影响，这种效应称为调制辨别干扰（MDI）。相反，当任务是检测添加到相同频率调制载波上的正弦信号时，共调制侧翼信号（与目标载波具有相同调制）的存在可以提高性能（共调制掩蔽释放：CMR）。本文研究了CMR和MDI如何受到侧翼信号数量和位置的影响。侧翼信号与目标信号的间隔为2倍等效矩形带宽（ERB），通过添加离目标更远的侧翼信号来控制其数量。窄带噪声（中心频率为10 Hz）用作所有载波的调制器。在实验1中，MDI任务要求检测目标调制深度（m）相对于0.7的参考值的降低。未调制的侧翼信号不影响阈值。调制的侧翼信号（m = 0.15）产生MDI，随着添加的侧翼信号增多，MDI增加。共调制侧翼信号产生的MDI通常比非共调制侧翼信号略大。CMR任务要求检测添加（相位为90度）到目标载波（m = 0.7）上的正弦信号。未调制的侧翼信号或与目标非共调制的侧翼信号对阈值没有影响。共调制侧翼信号（m = 0.7）产生CMR，通常随着添加的侧翼信号增多而增加。对于低于目标频率的侧翼信号，这种效应比高于目标频率的侧翼信号更大。实验2使用与实验1类似的刺激来研究MDI，不同之处在于任务是检测m相对于0.1的参考值的增加。即使是未调制的侧翼信号也会提高阈值，并且随着添加的侧翼信号增多，这种效应会增加，特别是在目标的高频侧。调制的侧翼信号（m = 0.2）会使阈值进一步增加，并且调制阈值通常随着添加侧翼信号的增多而增加。然而，MDI的量（调制侧翼信号和未调制侧翼信号的阈值之差）并没有随着侧翼信号数量的变化而系统地变化，并且在共调制和非共调制侧翼信号之间也没有显示出一致的差异。根据MDI和CMR背后的机制，特别是感知分组过程对结果进行了解释。
