Conflicts in language processing: a new perspective on the N400-P600 distinction

Conflicts in language processing often correlate with late positive event-related brain potentials (ERPs), particularly when they are induced by inconsistencies between different information types (e.g. syntactic and thematic/plausibility information). However, under certain circumstances, similar sentence-level interpretation conflicts (inanimate subjects) engender negativity effects (N400s) instead. The present ERP study was designed to shed light on this inconsistency. In previous studies showing monophasic positivities (P600s), the conflict was irresolvable and induced via a verb, whereas N400s were elicited by resolvable, argument-induced conflicts. Here, we therefore examined irresolvable argument-induced conflicts (pronoun case violations) in simple English sentences. Conflict strength was manipulated via the animacy of the first argument and the agreement status of the verb. Processing conflicts engendered a biphasic N400-late positivity pattern, with only the N400 sensitive to conflict strength (animacy). These results suggest that argument-induced conflicts engender N400 effects, (which we interpret in terms of increased competition for the Actor role) whereas irresolvable conflicts elicit late positivities (which we interpret as reflecting well-formedness categorisation).