Abstract/Summary

The rationale behind the present study comes from the assumption that the language proficiency level in the two languages of a bilingual are related (The Common Underlying Proficiency Theory; Cummins, 1980), and support in one language can be beneficial to the other (The Developmental Interdependence Hypothesis; Cummins, 1979). This study aims to investigate the relationship between the vocabulary size of sequential bilingual children in both of their languages (L1: Turkish, L2: English) and its relation to nonverbal intelligence scores. In addition, the study explores the effects of parental language dominance and home language use on the vocabulary size and nonverbal intelligence of bilingual children. The study involves 100 Turkish-English sequential bilingual children (aged 7-11) who were born and grew up in the UK and attend schools in which English is the language of formal instruction. The parents are middle-class (SES) first-generation immigrants from Turkey, and at least one parent of each child holds a higher educational degree. 25 English and 25 Turkish monolingual children (aged 7-11) were also involved in this study. The bilingual children were tested with the English X-Lex receptive vocabulary size test (Meara & Milton, 2003), the Turkish X-Lex (developed for this study) and a productive vocabulary test (Verbal Fluency Test) in both of their languages. The monolingual children were tested with the same tests in their languages. Raven’s Progressive Matrices (Raven, Raven, & Court, 2004) were used to measure the intelligence levels of the bilingual and monolingual children. In addition, the Parental Language Dominance Questionnaire (Dunn & Fox-Tree, 2009), the Language and Social Background Questionnaire (Luk & Bilaystok, 2013) and Language Usage Questionnaire (developed for this study) were administered to the parents of the bilingual children. The results demonstrate a clear relationship between the vocabulary size scores of bilingual children in both languages. Bilingual children with a larger vocabulary in Turkish also showed a larger vocabulary in English. The findings show that bilingual children have a lower vocabulary size than monolingual children in each language separately, but when Total Conceptual Vocabulary (TCV) is taken into account, there is no significant difference between the productive vocabulary sizes of bilingual and monolingual children, and no vocabulary ‘gap’ between monolingual and bilingual children. The receptive vocabulary sizes in both languages are significantly related with nonverbal intelligence scores, and the relation between productive vocabulary sizes and nonverbal intelligence scores approaches significance, and the language dominance of parents and their home language use has a positive influence on the vocabulary size and nonverbal intelligence scores of the bilingual children. Turkish dominant parents and those using more Turkish at home are positively correlated with bilingual children’s vocabulary size in both languages and nonverbal intelligence scores. Overall, the results of the study provide a clear evidence for the CUP theory and Interdependence Hypothesis in the area of vocabulary knowledge in terms of the relationship between the vocabulary sizes of bilingual children, and there is no bilingual disadvantage with regard to vocabulary size when both languages are considered. The results also show that nonverbal intelligence and vocabulary knowledge are related, and that a positive attitude of parents towards the minority language in an immigrant setting (Turkish in this case) has a positive effect on vocabulary size in both languages and on the nonverbal intelligence of bilingual children, and there is a bilingual cognitive advantage for children with more parental support for L1.