Bilingualism and cognitive development in relation to threshold theory

A study was conducted to examine the relationship between bilingualism and cognitive development, as predicted by threshold theory. This theory maintains that there may be levels of linguistic proficiency which bilingual children must attain in order to avoid cognitive deficits and to allow the cognitive benefits. On the whole, the results were consistent with the theory, in that an overall bilingual superiority was found only for those children who had attained a high degree of bilingualism. An overall bilingual superiority was not found for those children who had attained lower degrees of bilingualism. These results are discussed further in relation to Bialystok's model.The author is indebted to G. Tyson for valuable comments on an earlier version of this paper.