Department of Hearing and Speech Sciences, University of Maryland, College Park, MD, 20742, USA.
J Assoc Res Otolaryngol. 2020 Aug;21(4):373-391. doi: 10.1007/s10162-020-00753-4. Epub 2020 Jul 8.
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∫/ or fricative /ʃ/ 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.
老年人在安静环境中理解言语相对容易，但信号退化对言语理解的影响比对年轻人更大。这种困难可能部分源于与衰老过程相关的时间处理缺陷，以及/或者在听力正常或接近正常的言语频率范围内的听众中可能发生的高频听力损失。时间处理缺陷可能表现为外围和脑干/中脑结构中神经表示的降低，从而导致听觉皮层中响应强度的补偿或变化。对于信号的神经表示如何通过与年龄相关的皮质补偿机制得到改善或恢复，人们知之甚少。因此，我们使用语音编码来模拟频谱退化，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，我们使用了单词 DITCH 和 DISH 之间元音和最后的塞擦音 /t∫/ 或擦音 /ʃ/ 之间的无声间隔的闭合持续时间。我们获得了未处理和语音编码版本的这些单词的感知识别函数和电生理神经测量（频率跟随反应（FFR）和皮质听觉诱发电位（CAEP）），这些单词来自年轻的正常听力（YNH）、年长的正常或接近正常听力（ONH）和年长的听力障碍（OHI）听众。我们发现，语音编码仅在 OHI 听众中显着降低了感知识别函数的斜率。与语音编码对感知性能的有限影响相反，语音编码对 FFR 具有强大的影响，使得刺激与响应的相关性和包络幅度对于语音编码与未处理条件显著降低。对于 ONH 和 OHI 听众，都发现语音编码刺激的 P1 峰值幅度增加，但对于 YNH 听众则没有。这些结果表明，尽管语音编码大大降低了中脑言语刺激的早期神经表示，但在老年听众中可能存在皮质补偿，而在年轻听众中则不存在。
