N400 signatures of presupposition and assertion correlate with pragmatic mismatches, not with epistemic vigilance

This study investigates the N400 component, first identified in response to the presupposition of unshared information compared to the presupposition of shared information and the assertion of unshared information. Two hypotheses were tested: (i) the N400 only represents a pragmatic mismatch due to a less predicted informational packaging associated with some content, or (ii) it reflects variations in critical attention under different packaging conditions. Our findings support the first hypothesis. The N400 correlates with pragmatic mismatches between the linguistic encoding of content and its previous cognitive status, namely (1a) presupposition vs assertion of unshared information and (1b) presupposition of shared vs unshared information; and (2a) assertion vs presupposition of shared information and (2b) assertion of shared vs unshared information. The N400 is absent in equally matching conditions, i.e., the presupposition of shared content vs the assertion of unshared content (both matching) and the presupposition of unshared content vs the assertion of shared content (both mismatching). These conclusions offer insights into one of the key ERP components of language processing.