1 Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, NJ, USA.
2 Center for Neural Science, New York University, NY, USA.
Trends Hear. 2016 Jan-Dec;20:2331216516676255. doi: 10.1177/2331216516676255.
Hearing-impaired individuals experience difficulties in detecting or understanding speech, especially in background sounds within the same frequency range. However, normally hearing (NH) human listeners experience less difficulty detecting a target tone in background noise when the envelope of that noise is temporally gated (modulated) than when that envelope is flat across time (unmodulated). This perceptual benefit is called modulation masking release (MMR). When flanking masker energy is added well outside the frequency band of the target, and comodulated with the original modulated masker, detection thresholds improve further (MMR+). In contrast, if the flanking masker is antimodulated with the original masker, thresholds worsen (MMR-). These interactions across disparate frequency ranges are thought to require central nervous system (CNS) processing. Therefore, we explored the effect of developmental conductive hearing loss (CHL) in gerbils on MMR characteristics, as a test for putative CNS mechanisms. The detection thresholds of NH gerbils were lower in modulated noise, when compared with unmodulated noise. The addition of a comodulated flanker further improved performance, whereas an antimodulated flanker worsened performance. However, for CHL-reared gerbils, all three forms of masking release were reduced when compared with NH animals. These results suggest that developmental CHL impairs both within- and across-frequency processing and provide behavioral evidence that CNS mechanisms are affected by a peripheral hearing impairment.
听力受损的个体在检测或理解言语方面存在困难，尤其是在同一频率范围内的背景声音中。然而，正常听力（NH）的人类听众在背景噪声中检测目标音时，如果噪声的包络是时间门控（调制）的，而不是整个时间都平坦（未调制）的，那么他们的检测难度会小一些。这种感知优势被称为调制掩蔽释放（MMR）。当加在目标频率之外的掩蔽器能量与原始调制掩蔽器同时调制时，检测阈值会进一步提高（MMR+）。相比之下，如果加在目标频率之外的掩蔽器与原始掩蔽器反调制，那么阈值会恶化（MMR-）。这些在不同频率范围内的相互作用被认为需要中枢神经系统（CNS）的处理。因此，我们研究了发育性传导性听力损失（CHL）对沙鼠 MMR 特征的影响，作为对潜在 CNS 机制的测试。与未调制噪声相比，NH 沙鼠在调制噪声中的检测阈值更低。添加同时调制的侧翼进一步提高了性能，而反调制的侧翼则恶化了性能。然而，对于 CHL 饲养的沙鼠，与 NH 动物相比，所有三种形式的掩蔽释放都减少了。这些结果表明，发育性 CHL 损害了频率内和频率间的处理能力，并提供了行为证据，表明 CNS 机制受到外周听力损伤的影响。
