Graded and ungraded expectation patterns: Prediction dynamics during active comprehension.

Language comprehension can be facilitated by the accurate prediction of upcoming words, but prediction effects are not ubiquitous, and comprehenders likely use predictive processing to varying degrees depending on task demands. To ascertain the processing consequences of prioritizing prediction, we here compared ERPs elicited when young adult participants simply read for comprehension with those collected in a subsequent block that required active prediction. We were particularly interested in frontally-distributed post-N400 effects for expected and unexpected words in strongly constraining contexts, which have previously been documented as two distinct patterns: an enhanced positivity ("anterior positivity") observed for prediction violations compared to words that are merely unpredictable (because they occur in weakly constraining sentences) and a distinction between expected endings in more constraining contexts and those same weakly constrained words ("frontal negativity" to the strongly predicted words). We found that the size of the anterior positivity effect was unchanged between passive comprehension and active prediction, suggesting that some processes related to prediction may engage state-like networks. On the other hand, the frontal negativity showed graded patterns from the interaction of task and sentence type. These differing patterns support the hypothesis that there are two separate effects with frontal scalp distributions that occur after the N400 and further suggest that the impact of violating predictions (as long as prediction is engaged at all) is largely stable across varying levels of effort/attention directed toward prediction, whereas other comprehension processes can be modulated by task demands.

The fate of the unexpected: Consequences of misprediction assessed using ERP repetition effects.

Amid increasing interest in the role of prediction in language comprehension, there remains a gap in our understanding of what happens when predictions are disconfirmed. Are unexpected words harder to process and encode because of interference from the original prediction? Or, because of their relevance for learning, do expectation violations strengthen the representations of unexpected words? In two experiments, we used event-related potentials to probe the downstream consequences of prediction violations. Critical words were unexpected but plausible completions of either strongly constraining sentences, wherein they constituted a prediction violation, or weakly constraining sentences that did not afford a clear prediction. Three sentences later the critical word was repeated at the end of a different, weakly constraining sentence. In Experiment 1, repeated words elicited a reduced N400 and an enhanced late positive complex (LPC) compared to words seen for the first time. Critically, there was no effect of initial sentence constraint on the size of the repetition effect in either time window. Thus, prediction violations did not accrue either costs or benefits for later processing. Experiment 2 used the same critical items and added strongly constraining filler sentences with expected endings to further promote prediction. Again, there was no effect of initial sentence constraint on either the N400 or the LPC to repeated critical words. When taken with prior findings, the results suggest that prediction is both powerful and flexible: It can facilitate processing of predictable information by reducing encoding effort without causing processing difficulties for unexpected inputs.