Most brain imaging studies of language comprehension focus on activity following upon 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 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 to 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 N400 responses, 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 reflect specific aspects of prediction, as they are relevant in the processing of language and thought. Here, we show that, when critical words are embedded in predictive sentence contexts, a predictive brain response reflects specific meaning features of 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 (for example the words “lick” or “pick”) and between affirmative and negated sentence meanings.
We thank Verena Büscher and Dr Jeff Hanna for their help at different stages of this work. This work was supported by the Deutsche Forschungsgemeinschaft (Pu 97/16-1, Pu 97/22-1). Funding to pay the Open Access publication charges for this article was provided by the Deutsche Forschungsgemeinschaft.
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