This is the first Japanese-English Bilingual First Language Acquisition (BFLA) longitudinal study carried out within the framework of Processability Theory (Pienemann, 1998a, 2005). The informant of this study is a girl growing up bilingually in an Australian family within a one-parent-one-language environment from birth, where the mother is a Japanese native speaker and the father an English native speaker in an English-dominant community. The corpus consists of naturally spoken production of English and Japanese by the child, collected over 3 years and 9 months from age 1;11 (one year and eleven month) to 4;10.
The present study investigates her lexical development, the acquisition of morphology and syntax in the two languages, and further examines the relationships between lexical and grammatical development within each of the two languages. The study addresses one of the main issues in the field of BFLA; ‘does a bilingual child develop the two languages separately from the beginning?’ Results indicate that both Japanese and English of the child developed in the sequence predicted by PT, and that for one bilingual child, Japanese and English each developed in parallel but in a separate manner.