The speech of an older preschool bilingual sibling's influence and impact on the language development of a younger potential bilingual infant sibling

Although bilingual language development in an individual has been broadly studied, the phenomenon in between young bilingual siblings is relatively understudied and unknown. The proficiency of a bilingual depends on various factors such as birth order, parent's level of education, age of acquisition and environment. However, the greatest influence which is paramount to bilingual toddlers in early childhood becoming proficient speakers in both languages is due to the quantity and quality of input received. Whilst a sibling's presence is said to increase linguistic exposure, it remains unclear exactly how an older bilingual sibling's language use affects a younger sibling. This thesis reports on a case study which investigates the language choice of two siblings simultaneously acquiring Japanese and English. Using audio recordings of naturalistic interactions during everyday activities, we examine the siblings' interactions to determine the triggers and nature of code switching to determine whether the older sibling is influencing the language choices of the younger sibling. Where, when and with whom the siblings use which language will also be discussed. Lastly, we also discuss how the siblings use their language to assert their position in the family.