Grisoni Luigi, Miller Tally McCormick, Pulvermüller Friedemann
Brain Language Laboratory, Department of Philosophy and Humanities, Freie Universität Berlin, 14195 Berlin, Germany,
Brain Language Laboratory, Department of Philosophy and Humanities, Freie Universität Berlin, 14195 Berlin, Germany.
J Neurosci. 2017 May 3;37(18):4848-4858. doi: 10.1523/JNEUROSCI.2800-16.2017. Epub 2017 Apr 14.
Most brain-imaging studies of language comprehension focus on activity following meaningful stimuli. Testing adult human participants with high-density EEG, we show that, already before the presentation of a critical word, context-induced semantic predictions are reflected by a neurophysiological index, which we therefore call the semantic readiness potential (SRP). The SRP precedes critical words if a previous sentence context constrains the upcoming semantic content (high-constraint contexts), but not in unpredictable (low-constraint) contexts. Specific semantic predictions were indexed by SRP sources within the motor system-in dorsolateral hand motor areas for expected hand-related words (e.g., "write"), but in ventral motor cortex for face-related words ("talk"). Compared with affirmative sentences, negated ones led to medial prefrontal and more widespread motor source activation, the latter being consistent with predictive semantic computation of alternatives to the negated expected concept. Predictive processing of semantic alternatives in negated sentences is further supported by a negative-going event-related potential at ∼400 ms (N400), which showed the typical enhancement to semantically incongruent sentence endings only in high-constraint affirmative contexts, but not to high-constraint negated ones. These brain dynamics reveal the interplay between semantic prediction and resolution (match vs error) processing in sentence understanding. Most neuroscientists agree on the eminent importance of predictive mechanisms for understanding basic as well as higher brain functions. This contrasts with a sparseness of brain measures that directly reflects specific aspects of prediction, as they are relevant in the processing of language and thought. Here we show that when critical words are strongly expected in their sentence context, a predictive brain response reflects meaning features of these anticipated symbols already before they appear. The granularity of the semantic predictions was so fine grained that the cortical sources in sensorimotor and medial prefrontal cortex even distinguished between predicted face- or hand-related action words (e.g., the words "lick" or "pick") and between affirmative and negated sentence meanings.
大多数关于语言理解的脑成像研究都聚焦于有意义刺激之后的活动。我们通过高密度脑电图对成年人类参与者进行测试，结果表明，在关键单词呈现之前，语境诱导的语义预测就已通过一种神经生理指标得以体现，我们将其称为语义准备电位（SRP）。如果前一个句子语境对即将出现的语义内容有约束（高约束语境），SRP会先于关键单词出现，但在不可预测的（低约束）语境中则不会。特定的语义预测通过运动系统内的SRP源进行索引——对于预期与手相关的单词（如“write”），其源位于背外侧手部运动区，但对于与面部相关的单词（“talk”），其源位于腹侧运动皮层。与肯定句相比，否定句会导致内侧前额叶和更广泛的运动源激活，后者与对否定预期概念的替代方案进行预测性语义计算一致。否定句中语义替代方案的预测性处理还得到了约400毫秒时的负向事件相关电位（N400）的进一步支持，该电位仅在高约束肯定语境中对语义不一致的句子结尾表现出典型增强，而在高约束否定语境中则未表现出这种增强。这些脑动力学揭示了句子理解中语义预测与解析（匹配与错误）处理之间的相互作用。大多数神经科学家都认同预测机制对于理解基本以及高级脑功能具有至关重要的意义。这与直接反映预测特定方面的脑测量指标稀少形成对比，而这些指标在语言和思维处理中是相关的。在这里我们表明，当关键单词在其句子语境中被强烈预期时，一种预测性脑反应在这些预期符号出现之前就已反映出它们的意义特征。语义预测的粒度非常精细，以至于感觉运动皮层和内侧前额叶皮层中的皮层源甚至能够区分预测的与面部或手部相关的动作单词（如“lick”或“pick”）以及肯定和否定的句子含义。
