Data from: Electrophysiological correlates of semantic dissimilarity reflect the comprehension of natural, narrative speech.

People routinely hear and understand speech at rates of 120–200 words per minute [1, 2]. Thus, speech comprehension must involve rapid, online neural mechanisms that process words’ meanings in an approximately time-locked fashion. However, in the context of continuous speech, electrophysiological evidence for such time-locked processing has been lacking. Whilst valuable insights into the semantic processing of speech have been provided by the “N400 component” of the event-related potential [3-6], this literature has been dominated by paradigms using incongruous words within specially constructed sentences, and may not accurately reflect natural, narrative speech comprehension. Building on the discovery that cortical activity “tracks” the dynamics of running speech [7-9], and psycholinguistic work both demonstrating [10-12] and modeling [13-15] how context rapidly impacts on word processing, we describe a new approach for deriving an electrophysiological correlate of natural speech comprehension. We used a computational model [16] to quantify the meaning carried by each word based on how semantically dissimilar it was to its preceding context and then regressed this quantity against electroencephalographic (EEG) data recorded from subjects as they listened to narrative speech. This produced a prominent negativity at a time-lag of 200–600 ms on centro-parietal EEG channels, characteristics common to the N400. Applying this approach to EEG datasets involving time-reversed speech, cocktail party attention and audiovisual speech-in-noise demonstrated that this response was very sensitive to whether or not subjects understood the speech they heard. These findings demonstrate that, when successfully comprehending natural speech, the human brain responds to the contextual semantic content of each word in a relatively time-locked fashion.

人类日常感知并理解言语的速率可达120~200词/分钟[1,2]。因此，言语理解必然依赖快速的在线神经机制，以近似时间锁定的方式加工词汇语义。然而，在连续言语场景中，此类时间锁定加工的电生理证据仍较为匮乏。尽管事件相关电位（event-related potential, ERP）的N400成分（N400 component）[3-6]为言语语义加工提供了诸多宝贵洞见，但相关研究多采用在人工构建语句中嵌入语义不一致词汇的实验范式，或无法准确反映自然叙事性言语的理解过程。基于皮层活动可“追踪”连续言语动态[7-9]的发现，以及一系列证明[10-12]并建模[13-15]语境如何快速影响词汇加工的心理语言学研究，我们提出了一种用于提取自然言语理解电生理相关指标的新方法。我们借助计算模型[16]，通过计算目标词汇与前文语境的语义相似度，量化每个词汇承载的语义信息量，并将该量化值与受试者聆听叙事性言语时记录的脑电图（electroencephalogram, EEG）数据进行回归分析。该分析在中央顶叶脑电通道上于200~600ms时窗内引出了显著的负向电位，其特征与N400成分高度一致。将该方法应用于包含时间反转言语、鸡尾酒会注意力任务以及噪声下视听言语的EEG数据集后发现，该电位响应对受试者是否理解所聆听言语具有高度敏感性。上述结果表明，在成功理解自然言语时，人类大脑会以相对时间锁定的方式对每个词汇的语境语义内容做出响应。