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.