SISSA International School for Advanced Studies, via Bonomea 265, 34136 Trieste, Italy.
J R Soc Interface. 2012 Feb 7;9(67):328-38. doi: 10.1098/rsif.2011.0289. Epub 2011 Jun 29.
Understanding a word in context relies on a cascade of perceptual and conceptual processes, starting with modality-specific input decoding, and leading to the unification of the word's meaning into a discourse model. One critical cognitive event, turning a sensory stimulus into a meaningful linguistic sign, is the access of a semantic representation from memory. Little is known about the changes that activating a word's meaning brings about in cortical dynamics. We recorded the electroencephalogram (EEG) while participants read sentences that could contain a contextually unexpected word, such as 'cold' in 'In July it is very cold outside'. We reconstructed trajectories in phase space from single-trial EEG time series, and we applied three nonlinear measures of predictability and complexity to each side of the semantic access boundary, estimated as the onset time of the N400 effect evoked by critical words. Relative to controls, unexpected words were associated with larger prediction errors preceding the onset of the N400. Accessing the meaning of such words produced a phase transition to lower entropy states, in which cortical processing becomes more predictable and more regular. Our study sheds new light on the dynamics of information flow through interfaces between sensory and memory systems during language processing.
理解语境中的单词依赖于一系列感知和概念过程，从特定于模态的输入解码开始，最终将单词的意义统一到话语模型中。将感觉刺激转化为有意义的语言符号的一个关键认知事件是从记忆中获取语义表示。关于激活单词的意义会给皮质动态带来什么变化，我们知之甚少。我们在参与者阅读句子时记录了脑电图（EEG），这些句子可能包含一个语境中意想不到的单词，例如“cold”在“In July it is very cold outside”中。我们从单试 EEG 时间序列重建相空间轨迹，并将三种非线性可预测性和复杂性度量应用于语义访问边界的每一侧，该边界估计为关键单词诱发的 N400 效应的起始时间。与对照相比，意想不到的单词在 N400 开始之前与更大的预测误差相关。访问这些单词的含义会导致向更低熵状态的相变，其中皮质处理变得更可预测和更规则。我们的研究为语言处理过程中感官和记忆系统之间界面信息流的动态提供了新的视角。
