The N400 as an index of lexical preactivation and its implications for prediction in language comprehension

The N400 component's amplitude is standardly reduced for predictable words. But it is not clear whether this reduction truly reflects preactivation of the critical word or whether it just indexes the difficulty of integrating the word with the sentence. To adjudicate between these two accounts, event-related potentials were recorded while participants read short stories. In half of the stories, just before the story-final sentence, we induced an explicit prediction of a congruent or an incongruent target word, thereby preactivating this word. Inducing prediction for the incongruent target word eliminated the N400, fully supporting the preactivation theory. This implies that the N400 is a marker of prediction and that prediction is an essential aspect of sentence comprehension. In addition, an analysis of the ERPs on the words preceding the critical target word provides evidence on how the target word becomes preactivated by the context.

可预测词汇的N400成分（N400 component）波幅通常会降低，但目前尚不明确这种波幅降低究竟是真实反映了关键词汇的预激活（preactivation），还是仅表征了该词汇与句子的整合难度。为厘清这两种假说的正误，研究人员在被试阅读短篇故事时记录了事件相关电位（event-related potentials, ERPs）。在半数故事的句末句子之前，研究者会诱导被试对匹配（congruent）或不匹配（incongruent）的目标词汇产生明确预期，从而预激活该目标词。对不匹配目标词汇的预期诱导消除了N400效应，这一结果完全支持预激活理论。这一发现表明，N400可作为预测过程的标志物，而预测亦是句子理解的核心环节。此外，对关键目标词汇之前的词汇所对应的事件相关电位的分析，也为语境如何预激活目标词汇提供了实证依据。