Aubanel Vincent, Davis Chris, Kim Jeesun
MARCS Institute for Brain, Behaviour and Development, Western Sydney University Penrith, NSW, Australia.
Front Hum Neurosci. 2016 Aug 31;10:430. doi: 10.3389/fnhum.2016.00430. eCollection 2016.
A growing body of evidence shows that brain oscillations track speech. This mechanism is thought to maximize processing efficiency by allocating resources to important speech information, effectively parsing speech into units of appropriate granularity for further decoding. However, some aspects of this mechanism remain unclear. First, while periodicity is an intrinsic property of this physiological mechanism, speech is only quasi-periodic, so it is not clear whether periodicity would present an advantage in processing. Second, it is still a matter of debate which aspect of speech triggers or maintains cortical entrainment, from bottom-up cues such as fluctuations of the amplitude envelope of speech to higher level linguistic cues such as syntactic structure. We present data from a behavioral experiment assessing the effect of isochronous retiming of speech on speech perception in noise. Two types of anchor points were defined for retiming speech, namely syllable onsets and amplitude envelope peaks. For each anchor point type, retiming was implemented at two hierarchical levels, a slow time scale around 2.5 Hz and a fast time scale around 4 Hz. Results show that while any temporal distortion resulted in reduced speech intelligibility, isochronous speech anchored to P-centers (approximated by stressed syllable vowel onsets) was significantly more intelligible than a matched anisochronous retiming, suggesting a facilitative role of periodicity defined on linguistically motivated units in processing speech in noise.
越来越多的证据表明，大脑振荡跟踪言语。这种机制被认为是通过将资源分配给重要的言语信息来最大化处理效率，从而有效地将言语解析为适当粒度的单元以便进一步解码。然而，这种机制的某些方面仍不清楚。首先，虽然周期性是这种生理机制的固有属性，但言语只是准周期性的，因此尚不清楚周期性在处理中是否会带来优势。其次，从言语幅度包络的波动等自下而上的线索到句法结构等高阶语言线索，言语的哪个方面触发或维持皮层同步仍存在争议。我们展示了一项行为实验的数据，该实验评估了言语等时重定时对噪声中言语感知的影响。为言语重定时定义了两种类型的锚点，即音节起始点和幅度包络峰值。对于每种锚点类型，重定时在两个层次水平上进行，一个是约2.5Hz的慢时间尺度，另一个是约4Hz的快时间尺度。结果表明，虽然任何时间扭曲都会导致言语可懂度降低，但以P中心（由重读音节元音起始点近似）为锚点的等时言语比匹配的不等时重定时明显更易懂，这表明基于语言动机单元定义的周期性在噪声中处理言语时具有促进作用。
