Behavioural studies investigating word processing in bilinguals generally report faster response times (RTs) for first (L1) than for second (L2) language words. To examine the locus of this language effect, this study used behavioural data and event-related potentials (ERPs) collected from bilinguals while performing a semantic categorisation task on visual word pairs. RTs revealed both language and semantic relatedness effects. Spatio-temporal analysis of ERP map series showed that the semantic effect was explained by a condition-specific map segment occurring during the N400 component. The language effect was primarily explained by a map segment that started at ~170 ms and covered the period of the P2 component, that was longer in L2 than in L1 and whose duration correlated with RTs. Source localisation showed that this early segment involved the bilateral occipito-temporal regions including the fusiform area. These findings indicate that ERPs differentiated L1 and L2 during early word recognition steps.
