Is there a relation between onset age of bilingualism and enhancement of cognitive control?

TLDR

The study examined English proficiency, language use history, and flanker task performance in English‑speaking monolinguals and bilinguals, dividing bilinguals into early (before age 10) and late (after age 10) groups. Early bilinguals matched monolinguals in proficiency but showed the smallest flanker effect, and onset age of bilingualism was negatively correlated with proficiency and positively with the flanker effect, indicating a gradient of cognitive control advantage with more bilingual experience.

Abstract

Young English-speaking monolingual and bilingual adults were examined for English proficiency, language use history, and performance on a flanker task. The bilinguals, who were about twenty years old, were divided into two groups (early bilinguals and late bilinguals) according to whether they became actively bilingual before or after the age of ten years. Early bilinguals and monolinguals demonstrated similar levels of English proficiency, and both groups were more proficient in English than late bilinguals. In contrast, early bilinguals produced the smallest response time cost for incongruent trials (flanker effect) with no difference between monolinguals and late bilinguals. Moreover, across the whole sample of bilinguals, onset age of active bilingualism was negatively correlated with English proficiency and positively correlated with the flanker effect. These results suggest a gradient in which more experience in being actively bilingual is associated with greater advantages in cognitive control and higher language proficiency.