Co-activation of syntax in bilingual language production

We report four experiments that examined whether bilinguals' production of one language is affected by the syntactic properties of their other language. Greek-English and English-Greek highly proficient fluent bilinguals produced sentence completions following subject nouns whose translation had either the same or different number. We manipulated whether participants produced completions in the same language as the subject (the source language; one-language production) or the other language (the non-source language; two-language production), and whether they used only one language or both languages within the experimental session. The results demonstrated that the grammar systems of both languages were activated during both one-language and two-language production. The effects of the non-source language were particularly enhanced in two-language utterances, when both languages were used in the experiment, and when it was the bilinguals' native language. We interpret our results in terms of a model of bilingual sentence production.