Whereas behavioral studies of L2 acquisition in children are abundant little is known about second language (L2) processing in development neurocognitively. Indeed, neurocognitive studies of L2 processing typically are limited to adults with several years of exposure, who may use general cognitive mechanisms to compensate for any difficulties in L2 processing. Research on bilingual adults suggests that age of acquisition (AoA) and proficiency have different effects on different aspects of L2 processing. In addition to AoA and proficiency, neurocognitive studies have also reported on crosslinguistic influence (CLI) in morphosyntactic L2 processing. These studies typically report that learners display nativelike L2-processing when structures are similar to that of their own native language.

I will present studies where we recorded event-related brain potentials (ERPs) in order to index processing of phonological awareness (Rhyming effect: RE), semantics (N400), and syntax (LAN, P600) in bilingual and monolingual children 6-8 years of age. In addition, I will present a study of CLI effects of processing of L2-syntax. Even though behaviorally, bilingual children with an average AoA of 4 years had lower English proficiency than monolingual children, proficiency predicted similar differences in ERPs across groups. However, other differences in the ERPs waveforms were related to AoA rather than proficiency. These differences were restricted to phonological awareness and syntax. Adults with similar L2-Swedish proficiency differed in their processing depending on if their first language had similar syntax (verb second, German learners) or not (English learners).

The results from the studies that will be presented suggest early acquisition is important for processing of rhyming and for more automatic syntactic processing while proficiency is important for semantics and for controlled aspects of syntactic processing in children and that CLI can affect syntactic processing in late adult learners of a language.