Event-related potentials index lexical retrieval (N400) and integration (P600) during language comprehension

•The functional interpretation of the N400 and the P600 is still a matter of debate.•In a single ERP study, we tested the competing hypotheses about both components.•The results show that the N400 indexes retrieval rather than integration processes.•The P600 indexes general integration difficulty, not syntactic processes alone.•Findings suggest spatiotemporal overlap between the N400 and P600 components. The functional interpretation of two salient language-sensitive ERP components – the N400 and the P600 – remains a matter of debate. Prominent alternative accounts link the N400 to processes related to lexical retrieval, semantic integration, or both, while the P600 has been associated with syntactic reanalysis or, alternatively, to semantic integration. The often overlapping predictions of these competing accounts in extant experimental designs, however, has meant that previous findings have failed to clearly decide among them. Here, we present an experiment that directly tests the competing hypotheses using a design that clearly teases apart the retrieval versus integration view of the N400, while also dissociating a syntactic reanalysis/reprocessing account of the P600 from semantic integration. Our findings provide support for an integrated functional interpretation according to which the N400 reflects context-sensitive lexical retrieval – but not integration – processes. While the observed P600 effects were not predicted by any account, we argue that they can be reconciled with the integration view, if spatio-temporal overlap of ERP components is taken into consideration.