The Time Course of Meaning Construction with Varying Expectations

The human brain is an amazing information processor that derives meaning from our environment quickly and effortlessly, but not passively. Instead, it does so interactively by preadapting to changes, recognizing and learning patterns, and forming expectations about the future. How does the brain combine influences from our external and internal milieu to construct meaning? Electrophysiological studies of semantic memory have identified the N400 event related potential—a neural correlate indexing semantic processing in the brain—sensitive to a variety of top-down and bottom-up influences; however, the mechanisms that explain volitional aspects of semantic meaning construction are not fully understood. To explore this, participants were visually shown sentences, with words presented one at a time, and evaluated whether the final words of sentences formed sensible (SC) or unconnected completions (UCs). Top-down expectancies were modulated using colored boxes that surrounded the words of each sentence cueing the participants to either expect a SC (green) or UC (orange). A neutral cue (purple) that did not indicate the completion type served as a baseline condition. Top-down expectancies were factorially crossed with completion type forming valid, invalid, and neutral conditions. Participants were more accurate when evaluating validly than invalidly cued sentences and selectively faster when solving validly cued sentences that were semantically congruent. The N400, as measured following the presentation of the final word, was modulated mainly by semantic congruency but not expectancy. These results suggest that top-down mediated expectancies do not affect neural signatures of semantic access, but ultimately affect processing responsible for resolving discrepancies between semantic congruency and expectancy.