Limits of variability in bilingual language processing: An event-related potential study of German and English verb morphology

Abstract Previous research has highlighted that supplementing standard group-level event-related potential analyses with assessments of individual variation can enhance our understanding of language-related brain activity. The present study pursues this approach by examining bilingual speakers’ brain responses to morphologically complex word forms in both their native (German, L1) and their second language (English, L2). We tested 108 bilingual speakers using an ERP violation paradigm examining overapplications of regular verb inflections (‘regularizations’) and of irregular ones (‘irregularizations’). We found a striking L1/L2 contrast within the same bilingual speakers, a left-anterior negativity for regularizations in the L1 and a positivity (P600) for both violation types in the L2. Consistent with previous research, individuals’ brain responses were found to vary along negativity-/positivity-dominant effects. However, the crucial L1/L2 contrast in participants’ brain responses to regularizations was stable across individual differences. We conclude that linguistic constraints, that is, violation type and language status (L1 vs. L2), limit individual variability.