Speech Perception, Cognition, and Hearing Laboratory, Department of Speech-Language-Hearing: Sciences and Disorders, University of Kansas, Lawrence, Kansas, USA.
Indiana Clinical and Translational Sciences Institute - TL1 Program.
Ear Hear. 2020 Sep/Oct;41(5):1144-1157. doi: 10.1097/AUD.0000000000000856.
Listening to speech in adverse listening conditions is effortful. Objective assessment of cognitive spare capacity during listening can serve as an index of the effort needed to understand speech. Cognitive spare capacity is influenced both by signal-driven demands posed by listening conditions and top-down demands intrinsic to spoken language processing, such as memory use and semantic processing. Previous research indicates that electrophysiological responses, particularly alpha oscillatory power, may index listening effort. However, it is not known how these indices respond to memory and semantic processing demands during spoken language processing in adverse listening conditions. The aim of the present study was twofold: first, to assess the impact of memory demands on electrophysiological responses during recognition of degraded, spoken sentences, and second, to examine whether predictable sentence contexts increase or decrease cognitive spare capacity during listening.
Cognitive demand was varied in a memory load task in which young adult participants (n = 20) viewed either low-load (one digit) or high-load (seven digits) sequences of digits, then listened to noise-vocoded spoken sentences that were either predictable or unpredictable, and then reported the final word of the sentence and the digits. Alpha oscillations in the frequency domain and event-related potentials in the time domain of the electrophysiological data were analyzed, as was behavioral accuracy for both words and digits.
Measured during sentence processing, event-related desynchronization of alpha power was greater (more negative) under high load than low load and was also greater for unpredictable than predictable sentences. A complementary pattern was observed for the P300/late positive complex (LPC) to sentence-final words, such that P300/LPC amplitude was reduced under high load compared with low load and for unpredictable compared with predictable sentences. Both words and digits were identified more quickly and accurately on trials in which spoken sentences were predictable.
Results indicate that during a sentence-recognition task, both cognitive load and sentence predictability modulate electrophysiological indices of cognitive spare capacity, namely alpha oscillatory power and P300/LPC amplitude. Both electrophysiological and behavioral results indicate that a predictive sentence context reduces cognitive demands during listening. Findings contribute to a growing literature on objective measures of cognitive demand during listening and indicate predictable sentence context as a top-down factor that can support ease of listening.
在不利的听力条件下听言语需要付出努力。对听力过程中认知剩余容量的客观评估可用作理解言语所需努力的指标。认知剩余容量既受听力条件下信号驱动需求的影响，也受口语处理内在的自上而下需求的影响，如记忆使用和语义处理。先前的研究表明，电生理反应，特别是α振荡功率，可能反映听力努力。然而，尚不清楚这些指标如何响应记忆和语义处理在不利听力条件下处理口语时的需求。本研究的目的有两个：首先，评估记忆需求对识别退化语音句子时电生理反应的影响；其次，研究可预测的句子语境是否会增加或减少听力过程中的认知剩余容量。
在一项记忆负荷任务中，改变认知需求，让年轻成年参与者（n=20）观看低负荷（一位数字）或高负荷（七位数字）的数字序列，然后听噪声编码的语音句子，这些句子是可预测的还是不可预测的，然后报告句子的最后一个单词和数字。分析了电生理数据的频域α振荡和时域事件相关电位，以及单词和数字的行为准确性。
在句子处理过程中测量，高负荷时α功率的事件相关去同步化（即更负）大于低负荷，不可预测句子时也大于可预测句子。对于句子末尾单词的 P300/晚期正复合（LPC）也观察到了互补模式，即高负荷时 P300/LPC 振幅比低负荷时小，不可预测时比可预测时小。在语音句子可预测的情况下，单词和数字的识别速度更快、准确性更高。
结果表明，在句子识别任务中，认知负荷和句子可预测性都调节认知剩余容量的电生理指标，即α振荡功率和 P300/LPC 振幅。电生理和行为结果都表明，可预测的句子语境减少了听力过程中的认知需求。研究结果为听力过程中认知需求的客观测量的不断增长的文献做出了贡献，并表明可预测的句子语境是一种自上而下的因素，可以支持听力的轻松程度。
