Hierarchical prediction has been proposed as a fundamental computational principle underlying neurocognitive processing. Here we ask whether the brain engages distinct neurocognitive mechanisms in response to inputs that fulfill versus violate strong predictions at different levels of representation during language comprehension. Participants read three-sentence scenarios in which the third sentence constrained for a broad event structure (e.g. {Agent caution animate-Patient}). Low constraint contexts did not constrain for any specific event/lexical item. High constraint contexts additionally constrained for a specific event and lexical item (e.g. a twosentence context about a beach, lifeguards and sharks constrained for the event, {Lifeguards cautioned Swimmers} and the specific lexical item, "swimmers"). We measured ERPs on critical nouns that fulfilled and/or violated each of these constraints. We found clear, dissociable effects to fulfilled semantic predictions (a reduced N400), to event/lexical prediction violations (an increased late frontal positivity), and to event structure/animacy prediction violations (an increased late posterior positivity/P600). We argue that the late frontal positivity reflects a large change in activation associated with successfully updating the comprehender's mental model with new unpredicted input. We suggest that the posterior late positivity/P600 reflects an initial failure to incorporate new unpredicted input into the comprehender's mental model, and possibly a reanalysis of the previous inputs in attempts to revise this model. Together, these findings provide strong evidence that confirmed and violated predictions at different levels of representation manifest as distinct spatiotemporal neural signatures. and different tasks -all factors that are known to modulate the N400 and late positivity components. This made it difficult to compare the effects across different studies. However, based on a review of the early literature, Van Petten and Luka (2012) noted that, while both the late frontal and posterior positivity effects were associated with unexpected linguistic input, the main factor that distinguished between them was the plausibility of the resulting interpretation.This was confirmed in recent studies showing that, in high constraint contexts, the same individuals who produced a late frontal positivity effect on unexpected plausible critical words, produced a late posterior positivity effect on unexpected implausible critical words (in English