Turkish as an immigrant and heritage language in the UK: Effects of exposure and age at onset of bilingualism on grammatical and lexical development of the first language

Recent decades have brought an extensive amount of research that informs our understanding of the complex relationship between the languages in a multilingual mind and how this is shaped by biological, cognitive and external factors. The current study is an attempt to contribute to this understanding by providing a comprehensive picture of the structural and lexical development of Turkish as an immigrant and heritage language in the UK and its predictors. It specifically aims to gain insights into the roles of age at onset of bilingualism (AaO) and quantity/quality of L1 contact in this development by bringing together the body of research that was traditionally carried out separately either with early bilinguals/heritage speakers or late bilinguals (attriters). The spoken performance of a total of 92 Turkish - English bilinguals with a wide AaO range (0–42) divided into three age ranges and of 44 monolinguals was investigated. This approach allowed us to control for the quality of input available to the speakers within this community and test the impact of AaO to see whether these factors remain equally predictive of L1 knowledge across a wide range of linguistic abilities including past tense, overall structural complexity, foreign accentedness, and word formation. The synthesis of the findings obtained from three empirical studies written as chapters of this thesis suggested that this was not the case. The productivity in word formation, for example, was largely independent of AaO effect and past L1 experience, while both factors were at play in the remaining properties showing a dynamic, nonlinear interaction between the two. While in older bilinguals the transfer from the L2 to L1 was mostly subtle (due to late AaOs), for younger bilinguals, L1 development was variable and affected by a range of additional factors. Findings are discussed within the premises of various theoretical approaches.