Electrophysiological correlates of idiom comprehension: semantic composition does not follow lexical retrieval

We investigated the extent to which the literal meanings of the words forming literally-plausible idioms (e.g., break the ice) are retrieved from memory and semantically composed during sentence comprehension. Idiom strings were embedded in highly predictable, literal and idiomatic contexts. EEG data showed that the integration of the idiom’s conventional meaning occurred at the end of the expression and affected the Post-N400 Positivity. Time-Frequency Representation of the EEG clarified that prior to integrating the idiom’s meaning, an increase in power of higher gamma frequency band was associated only with literal processing. We argue that idioms comprehension proceeds in discrete steps: idiom recognition hampers semantic composition processes so that readers wait until the end of the expression to integrate the idiom meaning with the representation of the sentence.