Carlyon R P, Buus S, Florentine M
Communication Research Lab, Northeastern University, Boston, Massachusetts.
Hear Res. 1989 Oct;42(1):37-45. doi: 10.1016/0378-5955(89)90116-0.
To investigate the dependence of 'Comodulation Masking Release' (CMR) on the type and frequency of modulator, thresholds were measured for a 4-kHz tone masked by modulated and unmodulated noises. The maskers were a 400-Hz wide band of noise centered on 4 kHz (NOCUE), the same noise with a 2700-Hz lowpass noise added (LPCUE), and a wideband noise with a passband between 3 and 6 kHz (WBCUE). In each condition three types of modulator were used: a square wave, a sinewave, and a lowpass noise. Several frequencies of each type of modulator were used, allowing measurement of the interaction between envelope frequency (fe) and modulator type. Thresholds were lower in the presence than in the absence of modulation for all modulator types, except when fe was high (e.g. 100 Hz). The 'Modulated-Unmodulated Difference' (MUD) decreased monotonically with increasing fe in all conditions. For any given fe, MUDs generally were greater for square-wave and lowpass-noise modulation than for sinusoidal modulation. As significant MUDs were sometimes obtained even in the NOCUE condition, the MUD was not an accurate measure of CMR. Therefore, CMR was defined as the difference between the MUD obtained in the NOCUE condition and that obtained in each cue condition, for each combination of fe and modulator type. Measured this way, the CMR for our 4-kHz signals did not vary systemically with fc over the range studied. When a CMR was obtained it was smaller for sinusoidal modulation than for either square-wave or lowpass-noise modulation.(ABSTRACT TRUNCATED AT 250 WORDS)
为研究“共调制掩蔽释放”（CMR）对调制器类型和频率的依赖性，测量了由调制噪声和未调制噪声掩蔽的4千赫纯音的阈值。掩蔽音包括以4千赫为中心的400赫兹宽带噪声（NOCUE）、添加了2700赫兹低通噪声的相同噪声（LPCUE）以及通带在3至6千赫之间的宽带噪声（WBCUE）。在每种条件下，使用了三种类型的调制器：方波、正弦波和低通噪声。每种类型的调制器使用了几个频率，以便测量包络频率（fe）与调制器类型之间的相互作用。除fe较高（例如100赫兹）时外，所有调制器类型在有调制时的阈值均低于无调制时。在所有条件下，“调制 - 未调制差值”（MUD）均随fe的增加而单调下降。对于任何给定的fe，方波和低通噪声调制的MUD通常大于正弦调制。由于即使在NOCUE条件下有时也能获得显著的MUD，因此MUD并非CMR的准确度量。因此，CMR被定义为对于fe和调制器类型的每种组合，在NOCUE条件下获得的MUD与在每种提示条件下获得的MUD之间的差值。以这种方式测量，我们4千赫信号的CMR在所研究的范围内并未随fc系统性变化。当获得CMR时，正弦调制的CMR小于方波或低通噪声调制。（摘要截取自250字）
