Lexical versus conceptual anticipation during sentence processing: frontal positivity and N400 ERP components

Although the sensitivity of the N400 to semantic processing is well established, late positive ERP components are also elicited during sentence comprehension. We suggest that there are multiple such components differing in scalp topography, and that a larger frontal positivity often follows the larger N400 elicited by congruent but unexpected sentence endings as compared to predictable endings. We evaluated the lexical versus conceptual specificity of this post-N400-positivity. High- and low-constraint sentences were completed by the words most preferred by a normative group (best completions), by words that were nearly synonymous to those best completions, and by other congruent words that were semantically dissimilar to the best completions. The N400 was sensitive to both the predictability (cloze probability) of the words and their semantic similarity to the best completion, consistent with a sensitivity to conceptual expectations that could be fulfilled by alternate words. In contrast, an anterior positivity was elicited by all final words that were not highly predictable, independent of whether they were semantically similar or dissimilar to the most preferred word, indicating a sensitivity to specific lexical expectations.