Typicality effect on N400 ERP in categories despite differences in semantic processing

We investigate the effect of word typicality - the degree of membership of a word to its superordinate category - on the N400 event-related potential (ERP) using a single trial detection approach based on spatiotemporal beamforming. Unlike the norm in studies, where mostly concrete categories are used (imaginable objects), we considered a total of 6 basic categories: three abstract and unimaginable (emotion, event, illness), one abstract yet clearly imaginable (color), and two concrete categories, a coherent (mammals) and an incoherent one (furniture). We also investigated the source of the observed N400 ERPs in the brain to detect possible differences between the semantic processing of these categories. Our results show that, independently of word abstractness or concreteness, word typicality has a clear effect on N400 both in terms of amplitude and scalp localization as well as in N400 sources, all of which in turn is indicative of differences in difficulty of word processing.