Processing subject-verb agreement in a second language depends on proficiency.

Subject-verb agreement is a computation that is often difficult to execute perfectly in the first language (L1) and even more difficult to produce skillfully in a second language (L2). In this study, we examined the way in which bilingual speakers complete sentence fragments in a manner that reflects access to both grammatical and conceptual number. In two experiments, we show that bilingual speakers are sensitive to both grammatical and conceptual number in the L1 and grammatical number agreement in the L2. However, only highly proficient bilinguals are also sensitive to conceptual number in the L2. The results suggest that the extent to which speakers are able to exploit conceptual information during speech planning depends on the level of language proficiency.