Grant K W, Summers V, Leek M R
Walter Reed Army Medical Center, Army Audiology and Speech Center, Washington, DC 20307-5001, USA.
J Acoust Soc Am. 1998 Aug;104(2 Pt 1):1051-60. doi: 10.1121/1.423323.
Modulation detection and modulation rate discrimination thresholds were obtained at three different modulation rates (fm = 80, 160, and 320 Hz) and for three different ranges of modulation depths (m): full (100%), mid (70%-80%), and low (40%-60%) with both normal-hearing (NH) and hearing-impaired (HI) subjects. The results showed that modulation detection thresholds increased with modulation rate, but significantly more so for HI than for NH subjects. Similarly, rate discrimination thresholds (delta r) increased with increases in fm and decreases in modulation depth. When compared to NH subjects, rate discrimination thresholds for HI subjects were significantly worse for all rates and for all depths. At the fastest modulation rate with less than 100% modulation depth, most HI subjects could not discriminate any change in rate. When valid thresholds for rate discrimination were obtained for HI subjects, they ranged from 2.5 semitones (delta r = 12.7 Hz, fm = 80 Hz, m = 100%) to 8.7 semitones (delta r = 214.5 Hz, fm = 320 Hz, m = 100%). In contrast, average rate discrimination thresholds for NH subjects ranged from 0.9 semitones (delta r = 4.2 Hz, fm = 80 Hz, m = 100%) to 4.7 semitones (delta r = 103.5 Hz, fm = 320 Hz, m = 60%). Some of the differences in temporal processing between NH and HI subjects, especially those related to modulation detection, may be accounted for by differences in signal audibility, especially for high-frequency portions of the modulated noise. However, in many cases, HI subjects encountered great difficulty discriminating a change in modulation rate even though the modulation components of the standard and test stimuli were detectable.
在三种不同的调制率（fm = 80、160和320赫兹）以及三种不同的调制深度范围（m）下，分别针对正常听力（NH）和听力受损（HI）受试者获取了调制检测和调制率辨别阈值。调制深度范围包括全深度（100%）、中深度（70%-80%）和低深度（40%-60%）。结果表明，调制检测阈值随调制率增加而升高，但听力受损受试者的升高幅度显著大于正常听力受试者。同样，率辨别阈值（δr）随fm增加和调制深度减小而升高。与正常听力受试者相比，听力受损受试者在所有率和所有深度下的率辨别阈值都明显更差。在调制深度小于100%的最快调制率下，大多数听力受损受试者无法辨别率的任何变化。当为听力受损受试者获得有效的率辨别阈值时，其范围从2.5个半音（δr = 12.7赫兹，fm = 80赫兹，m = 100%）到8.7个半音（δr = 214.5赫兹，fm = 320赫兹，m = 100%）。相比之下，正常听力受试者的平均率辨别阈值范围从0.9个半音（δr = 4.2赫兹，fm = 80赫兹，m = 100%）到4.7个半音（δr = 103.5赫兹，fm = 320赫兹，m = 60%）。正常听力和听力受损受试者在时间处理方面的一些差异，尤其是与调制检测相关的差异，可能是由信号可听度的差异导致的，特别是对于调制噪声的高频部分。然而，在许多情况下，即使标准和测试刺激的调制成分是可检测的，听力受损受试者在辨别调制率变化时仍遇到很大困难。
