Differential Effects of Input Quantity and Input Quality on Bilingual Development: A Study with Kurdish–English Adolescents

Abstract

Previous research has shown that both input quantity and quality play a role in dual language learning. However, it is unclear whether input quantity factors (e.g., school input) and input quality factors (e.g., home media input) work similarly in the language development of bilinguals while other potential internal and external factors are controlled for. This paper addressed this issue through investigating the influence of input quantity and input quality factors, both at the individual and group levels, on morphosyntax, vocabulary size, and lexical access ability in the Kurdish-L1 and English-L2 of Kurdish–English bilingual adolescents. Data were collected via a battery of standardized and researcher-developed measures and a detailed questionnaire. The results from backward regressions revealed that higher parental Kurdish proficiency and more exposure to Kurdish input through siblings and reading activities were associated with better Kurdish morphosyntactic skill, while a larger Kurdish vocabulary size was predicted by more exposure to native-speaker input in Kurdish. Both more Kurdish input received in preschool/school and through Kurdish media were related to better lexical access ability in Kurdish. Further, more exposure to English input in preschool/school predicted better English morphosyntactic skill and a larger vocabulary size, whereas higher paternal English proficiency was associated with better lexical access ability in English. Hierarchical regression analyses showed that input quality was more important in explaining Kurdish morphosyntactic and vocabulary size skills and lexical access ability in both languages, while input quantity explained more variance in English morphosyntactic and vocabulary size skills. Out-of-class Kurdish input outweighed instructional input to a certain extent in relation to Kurdish skills and lexical access ability in English, while instructional English input was more important for English morphosyntax and vocabulary size.