Speech processing is supported by the synchronization of cortical oscillations to its rhythmic components, including syllable rate. This has been shown to be the case for normal rate speech as well as artificially accelerated speech. However, the case of natural speech rate variations, which are among the most ubiquitous sources of variability in speech, has been largely overlooked. Here, we directly compared changes in the properties of cortico-acoustic coupling when speech naturally shifts from normal to fast rate and when it is artificially accelerated. Neuromagnetic brain signals of 24 normal-hearing adults were recorded with magnetoencephalography (MEG) while they listened to natural normal (~6 syllables/s), natural fast (~9 syllables/s) and time-compressed (~9 syllables/s) sentences, as well as to envelope-matched amplitude-modulated noise. We estimated coherence between the envelope of the acoustic input and MEG source time-series at frequencies corresponding to the mean syllable rates of the normal and fast speech stimuli. We found that listening to natural speech at normal and fast rates was associated with coupling between speech signal envelope and neural oscillations in right auditory and (pre)motor cortices. This oscillatory alignment occurred at ~6.25 Hz for normal rate sentences and shifted up to ~8.75 Hz for naturally-produced fast speech, mirroring the increase in syllable rate between the two conditions. Unexpectedly, despite being generated at the same rate as naturally-produced fast speech, the time-compressed sentences did not lead to significant cortico-acoustic coupling at ~8.75 Hz. Interestingly, neural activity in putative right articulatory cortex exhibited stronger tuning to natural fast rather than to artificially accelerated speech, as well as stronger phase-coupling with left temporo-parietal and motor regions. This may reflect enhanced tracking of articulatory features of naturally-produced speech. Altogether, our findings provide new insights into the oscillatory brain signature underlying the perception of natural speech at different rates and highlight the importance of using naturally-produced speech when probing the dynamics of brain-to-speech coupling.

中文翻译：

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神经振荡跟踪自然的而不是人工的快速语音：使用MEG从语音-大脑耦合中获得的新见解

皮层振动与其节奏成分（包括音节速率）的同步支持语音处理。对于正常速率的语音以及人工加速的语音，情况已证明是这种情况。然而，自然语音速率变化的情况是语音变化的最普遍的来源之一，但这种情况在很大程度上被忽略了。在这里，我们直接比较了当语音自然地从正常速率转换为快速速率并且被人工加速时，皮质声学耦合特性的变化。用脑磁图（MEG）记录了24名听力正常的成年人的神经磁脑信号，同时他们听了自然正常（〜6个音节/ s），自然快（〜9个音节/ s）和时间压缩（〜9个音节/ s）句子，以及包络匹配的调幅噪声。我们估计了在对应于正常和快速语音刺激的平均音节速率的频率处，声音输入的包络和MEG源时间序列之间的相干性。我们发现，以正常和快速的速度收听自然语音与语音信号包络和右听觉皮层和（运动前）皮层神经振动之间的耦合有关。对于正常速率的句子，这种振荡对准发生在〜6.25 Hz，对于自然产生的快速语音，这种振荡对准上升至〜8.75 Hz，反映了两种情况之间音节速率的增加。出乎意料的是，尽管以与自然产生的快速语音相同的速率产生，但时间压缩的句子并没有在〜8.75 Hz的频率下导致显着的皮质声耦合。有趣的是，推定的右发音皮层的神经活动表现出更强的自然快速调节能力，而不是人为加速的语音调节能力，以及与左侧颞顶和运动区更强的相位耦合。这可以反映出对自然产生的语音的发音特征的增强跟踪。总而言之，我们的发现为以不同速率感知自然语音的振荡性脑信号提供了新的见解，并突出了在探究脑与语音耦合的动力学时使用自然产生的语音的重要性。