Knowledge Bank

By measuring the event-related brain potentials (ERPs) elicited during a visual word-by-word presentation of sentences containing either a syntactic incongruity, semantic incongruity, or a combined syntactic and semantic incongruity, I investigated whether the N400 and P600 waveforms are discrete components reflective of independent semantic and syntactic processing or simply sub-parts of a larger wave caused by general sentential processing difficulty. Words that were syntactically inconsistent with the sentence structure elicited a P600 potential, while words that were semantically inconsistent elicited an N400 potential. Words that caused both a syntactic and semantic violation of the sentence in which they appeared evoked both a P600 and an N400 waveform. The results support the hypothesis that the N400 and P600 are independent waveforms, suggesting that the brain is capable of responding specifically to anomalies at both the syntactic and semantic levels. These findings are used to evaluate the functionality of three currently popular descriptions of the relationship between the syntactic and semantic levels of the human language processor.