School of Engineering, Trinity Centre for Bioengineering, and Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland.
Department of Pediatrics and Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461.
eNeuro. 2018 Apr 16;5(2). doi: 10.1523/ENEURO.0084-18.2018. eCollection 2018 Mar-Apr.
In real-world environments, humans comprehend speech by actively integrating prior knowledge (P) and expectations with sensory input. Recent studies have revealed effects of prior information in temporal and frontal cortical areas and have suggested that these effects are underpinned by enhanced encoding of speech-specific features, rather than a broad enhancement or suppression of cortical activity. However, in terms of the specific hierarchical stages of processing involved in speech comprehension, the effects of integrating bottom-up sensory responses and top-down predictions are still unclear. In addition, it is unclear whether the predictability that comes with prior information may differentially affect speech encoding relative to the perceptual enhancement that comes with that prediction. One way to investigate these issues is through examining the impact of P on indices of cortical tracking of continuous speech features. Here, we did this by presenting participants with degraded speech sentences that either were or were not preceded by a clear recording of the same sentences while recording non-invasive electroencephalography (EEG). We assessed the impact of prior information on an isolated index of cortical tracking that reflected phoneme-level processing. Our findings suggest the possibility that prior information affects the early encoding of natural speech in a dual manner. Firstly, the availability of prior information, as hypothesized, enhanced the perceived clarity of degraded speech, which was positively correlated with changes in phoneme-level encoding across subjects. In addition, P induced an overall reduction of this cortical measure, which we interpret as resulting from the increase in predictability.
在现实环境中，人类通过主动将先前知识 (P) 和期望与感官输入相结合来理解言语。最近的研究揭示了先前信息在颞叶和额叶皮质区域的影响，并表明这些影响是由言语特定特征的增强编码而非皮质活动的广泛增强或抑制来支撑的。然而，就言语理解涉及的特定分层处理阶段而言，整合自上而下的感觉反应和自下而上的预测的影响仍不清楚。此外，先前信息带来的可预测性是否会相对于该预测带来的感知增强而对言语编码产生不同的影响尚不清楚。一种研究这些问题的方法是通过检查 P 对连续言语特征的皮质跟踪的指标的影响。在这里，我们通过向参与者呈现退化的句子来做到这一点，这些句子要么在同一句子的清晰记录之前，要么在记录非侵入性脑电图 (EEG) 的同时呈现。我们评估了先前信息对反映音素级处理的皮质跟踪的孤立指标的影响。我们的研究结果表明，先前信息可能以双重方式影响自然言语的早期编码。首先，如假设的那样，先前信息的可用性增强了退化语音的感知清晰度，这与受试者之间音素级编码的变化呈正相关。此外，P 导致该皮质测量值整体降低，我们将其解释为可预测性增加的结果。
