The notion of 'balanced' bilingual development has often been used to refer to two languages which are spoken with equal proficiency during bilingual language acquisition. However, it is still not known how 'equal' the proficiencies of the two languages should be in order to achieve 'balanced' bilingualism. This case study aims to capture this notion of 'balanced' by using the following quantitative measures with respect to grammatical development: mean length of utterance (MLU), upper bound (UB) and lexical diversity (D). Direct comparison between two sets of absolute values does not reliably predict a bilingual child's language dominance due to potential typological differences two languages. The obtained values of these measures are shown to be comparable with those of monolingual children acquiring each language, and thus it is argued that bilingual children who attain such competence in each language are considered as having 'balanced' bilingual development.
This study concerns particularly two aspects of bilingual children: a) grammatical development and b) language use in terms of mixing. With regard to a), given that cross-linguistic influence is attested across studies of bilingual language development, this case study investigates the domains of null objects and wh-interrogatives to see if any cross-linguistic influence takes place. The qualitative similarities found in all Cantonese-English bilingual subjects suggest that the nature of the cross-linguistic influence is similar, whereas the quantitative differences imply that language dominance has determining effect on the phenomenon.
Concerning b), since language proficiency is often taken as one of the crucial factors predicting language mixing pattern, this present study examines the relationship of the mixing pattern in the Cantonese-English balanced bilingual child and her language proficiency. The results show that mixing occurs more frequently in Cantonese context than in English context.