One challenge of learning a foreign language (L2) in adulthood is the mastery of syntactic structures that are implemented differently in L2 and one's native language (L1). Here, we asked how L2 speakers learn to process syntactic constructions that are in direct conflict between L1 and L2, in comparison to structures without such a conflict. To do so, we measured EEG during sentence reading in three groups of German learners of Dutch with different degrees of L2 experience (from 3 to more than 18 months of L2 immersion) as well as a control group of Dutch native speakers. They read grammatical and ungrammatical Dutch sentences that, in the conflict condition, contained a structure with opposing word orders in Dutch and German (sentence-final double infinitives) and, in the no-conflict condition, a structure for which word order is identical in Dutch and German (subordinate clause inversion). Results showed, first, that beginning learners showed N400-like signatures instead of the expected P600 for both types of violations, suggesting that, in the very early stages of learning, different neurocognitive processes are employed compared with native speakers, regardless of L1–L2 similarity. In contrast, both advanced and intermediate learners already showed native-like P600 signatures for the no-conflict sentences. However, their P600 signatures were significantly delayed in processing the conflicting structure, even though behavioral performance was on a native level for both these groups and structures. These findings suggest that L1–L2 word order conflicts clearly remain an obstacle to native-like processing, even for advanced L2 learners.

Learning the syntax of a second language (L2) often represents a big challenge to L2 learners. Previous research on syntactic processing in L2 has mainly focused on how L2 speakers respond to “objective” syntactic violations, that is, phrases that are incorrect by native standards. In this study, we investigate how L2 learners, in particular those of less than near-native proficiency, process phrases that deviate from their own, “subjective,” and often incorrect syntactic representations, that is, whether they use these subjective and idiosyncratic representations during sentence comprehension. We study this within the domain of grammatical gender in a population of German learners of Dutch, for which systematic errors of grammatical gender are well documented. These L2 learners as well as a control group of Dutch native speakers read Dutch sentences containing gender-marked determiner–noun phrases in which gender agreement was either (objectively) correct or incorrect. Furthermore, the noun targets were selected such that, in a high proportion of nouns, objective and subjective correctness would differ for German learners. The ERP results show a syntactic violation effect (P600) for objective gender agreement violations for native, but not for nonnative speakers. However, when the items were re-sorted for the L2 speakers according to subjective correctness (as assessed offline), the P600 effect emerged as well. Thus, rather than being insensitive to violations of gender agreement, L2 speakers are similarly sensitive as native speakers but base their sensitivity on their subjective—sometimes incorrect—representations.