Age-Related Compensation Mechanism Revealed in the Cortical Representation of Degraded Speech
Age-Related Compensation Mechanism Revealed in the Cortical Representation of Degraded Speech
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DOI：
10.1007/s10162-020-00753-4
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发表时间：
2020-07-08
影响因子：
2.4
通讯作者：
Goupell, Matthew J.
中科院分区：
文献类型：
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作者：
Anderson, Samira;Roque, Lindsey;Goupell, Matthew J.
老年人在安静时相对容易理解语音，但信号衰减比年轻人更能阻碍语音理解。这种困难可能部分归因于与老化过程相关的时间处理缺陷和/或高频听力损失，这些损失可能发生在在语音频率范围内具有正常或接近正常听力阈值的听众中。时间处理缺陷可能表现为外周和脑干/中脑结构中的神经表征退化，从而导致补偿或听觉皮层反应强度的变化。人们对于通过与年龄相关的皮层补偿机制改善或恢复信号的神经表征的过程知之甚少。因此，我们使用声码来模拟频谱退化，以比较在时间维度上对比的单词的行为和神经表示。具体来说，我们分别使用了单词 DITCH 和 DISH 的元音和最后的塞擦音 /t积分/ 或擦音 /?/ 之间的静音间隔的闭合持续时间。我们获得了年轻正常听力 (YNH)、老年正常或接近正常听力 (ONH) 和老年听力受损 (OHI) 听众对这些单词的未处理和声码版本的感知识别功能和电生理神经测量（频率跟随反应 (FFR) 和皮质听觉诱发电位 (CAEP)）。我们发现，声编码仅显着降低了 OHI 听众的感知识别函数的斜率。与声编码对感知表现的有限影响相反，声编码对跨年龄组的 FFR 具有强大的影响，使得声编码条件下的刺激与反应相关性和包络幅度显着低于未处理条件。 ONH 和 OHI 听众都发现声码刺激的 P1 峰值幅度增加，但 YNH 听众则没有。这些结果表明，虽然声码极大地降低了中脑中语音刺激的早期神经表征，但老年听众可能会出现年轻听众所没有的皮质补偿。
Older adults understand speech with comparative ease in quiet, but signal degradation can hinder speech understanding much more than it does in younger adults. This difficulty may result, in part, from temporal processing deficits related to the aging process and/or high-frequency hearing loss that can occur in listeners who have normal- or near-normal-hearing thresholds in the speech frequency range. Temporal processing deficits may manifest as degraded neural representation in peripheral and brainstem/midbrain structures that lead to compensation, or changes in response strength in auditory cortex. Little is understood about the process by which the neural representation of signals is improved or restored by age-related cortical compensation mechanisms. Therefore, we used vocoding to simulate spectral degradation to compare the behavioral and neural representation of words that contrast on a temporal dimension. Specifically, we used the closure duration of the silent interval between the vowel and the final affricate /t integral/ or fricative /?/ of the words DITCH and DISH, respectively. We obtained perceptual identification functions and electrophysiological neural measures (frequency-following responses (FFR) and cortical auditory-evoked potentials (CAEPs)) to unprocessed and vocoded versions of these words in young normal-hearing (YNH), older normal- or near-normal-hearing (ONH), and older hearing-impaired (OHI) listeners. We found that vocoding significantly reduced the slope of the perceptual identification function in only the OHI listeners. In contrast to the limited effects of vocoding on perceptual performance, vocoding had robust effects on the FFRs across age groups, such that stimulus-to-response correlations and envelope magnitudes were significantly lower for vocoded vs. unprocessed conditions. Increases in the P1 peak amplitude for vocoded stimuli were found for both ONH and OHI listeners, but not for the YNH listeners. These results suggest that while vocoding substantially degrades early neural representation of speech stimuli in the midbrain, there may be cortical compensation in older listeners that is not seen in younger listeners.