Kayser Stephanie J, Ince Robin A A, Gross Joachim, Kayser Christoph
Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, United Kingdom.
Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, United Kingdom
J Neurosci. 2015 Nov 4;35(44):14691-701. doi: 10.1523/JNEUROSCI.2243-15.2015.
The entrainment of slow rhythmic auditory cortical activity to the temporal regularities in speech is considered to be a central mechanism underlying auditory perception. Previous work has shown that entrainment is reduced when the quality of the acoustic input is degraded, but has also linked rhythmic activity at similar time scales to the encoding of temporal expectations. To understand these bottom-up and top-down contributions to rhythmic entrainment, we manipulated the temporal predictive structure of speech by parametrically altering the distribution of pauses between syllables or words, thereby rendering the local speech rate irregular while preserving intelligibility and the envelope fluctuations of the acoustic signal. Recording EEG activity in human participants, we found that this manipulation did not alter neural processes reflecting the encoding of individual sound transients, such as evoked potentials. However, the manipulation significantly reduced the fidelity of auditory delta (but not theta) band entrainment to the speech envelope. It also reduced left frontal alpha power and this alpha reduction was predictive of the reduced delta entrainment across participants. Our results show that rhythmic auditory entrainment in delta and theta bands reflect functionally distinct processes. Furthermore, they reveal that delta entrainment is under top-down control and likely reflects prefrontal processes that are sensitive to acoustical regularities rather than the bottom-up encoding of acoustic features.
The entrainment of rhythmic auditory cortical activity to the speech envelope is considered to be critical for hearing. Previous work has proposed divergent views in which entrainment reflects either early evoked responses related to sound encoding or high-level processes related to expectation or cognitive selection. Using a manipulation of speech rate, we dissociated auditory entrainment at different time scales. Specifically, our results suggest that delta entrainment is controlled by frontal alpha mechanisms and thus support the notion that rhythmic auditory cortical entrainment is shaped by top-down mechanisms.
慢节奏听觉皮层活动与言语中的时间规律同步被认为是听觉感知的核心机制。先前的研究表明，当声学输入质量下降时，同步会减弱，但同时也将相似时间尺度的节律活动与时间预期的编码联系起来。为了理解这些自下而上和自上而下对节律同步的贡献，我们通过参数化改变音节或单词之间停顿的分布来操纵言语的时间预测结构，从而使局部言语速率不规则，同时保持可懂度和声信号的包络波动。在人类参与者中记录脑电图活动，我们发现这种操纵并没有改变反映单个声音瞬态编码的神经过程，如诱发电位。然而，这种操纵显著降低了听觉δ（而非θ）频段与言语包络同步的保真度。它还降低了左额叶α波功率，并且这种α波降低可预测参与者之间δ频段同步的降低。我们的结果表明，δ和θ频段的节律性听觉同步反映了功能上不同的过程。此外，它们揭示了δ频段同步受自上而下的控制，并且可能反映了对声学规律敏感的前额叶过程，而非声学特征的自下而上编码。
节律性听觉皮层活动与言语包络的同步被认为对听力至关重要。先前的研究提出了不同观点，其中同步要么反映与声音编码相关的早期诱发反应，要么反映与预期或认知选择相关的高级过程。通过操纵言语速率，我们在不同时间尺度上分离了听觉同步。具体而言，我们的结果表明，δ频段同步受额叶α机制控制，因此支持节律性听觉皮层同步受自上而下机制塑造的观点。
