Bilingual effects in Mandarin-English bilingual adolescents

Abstract

Whether bilingualism confers non-linguistic cognitive benefits is hotly debated in the psychological sciences. Fueling this debate are previously-reported mixed findings, often only emerging for certain populations of bilinguals under specific testing conditions. Others argue that previously reported advantages likely result from differences in highly-correlated non-linguistic variables including socioeconomic status and education. This debate is further complicated by the use of methodological practices that ignore meaningful individual differences, typically viewing bilingualism as a categorical, unidimensional construct. The primary motivation of this thesis is to explore the veracity of the bilingual advantage in executive function in the population of bilinguals with the most inconsistent reported results: young people. Additionally, the work in this thesis aimed to address the methodological shortcomings of previous studies in order to draw stronger conclusions. To begin, an exhaustive scoping review of reported bilingual effects in young people was conducted to isolate commonly used methods. Included studies (n = 73), primarily conducted in Western countries using college-age samples, typically used between-groups designs and exclusively fixed-effects methods of analysis. Findings support the claim that mixed results may be due to the use of methods that ignore meaningful individual differences in language experience and task performance. This review also identified an almost complete lack of studies conducted in high-school-aged bilinguals, ignoring a crucial developmental stage. Findings from the scoping review and restrictions imposed by the global pandemic motivated the design of two Internet-based behavioral studies aimed at addressing gaps in the literature. These studies investigated the influence of bilingualism on executive function within a sample of Mandarin-English speaking bilingual adolescents in Mainland China (n = 41). Specifically, the influence of the degree of bilingualism on cognitive inhibition and attention was investigated. Data were analyzed using linear mixed-effects models to account for nontrivial differences in language experience and task performance. Across both studies, a bilingual advantage in monitoring on the flanker task and Attention Network Test (ANT) was associated with higher English proficiency, with supporting evidence observed on the Simon task. Evidence in support of a specific bilingual advantage in inhibition was limited to the Simon task, and was associated with higher levels of English language proficiency. Critically, a bilingual disadvantage was observed on the flanker task and the ANT, associated with higher dominance of English language use relative to Mandarin, apart from improved orienting correlated with this dominance ratio. Findings suggest dissociable dimensions of bilingualism differentially influence executive function and that mixed reports in the literature may result as a consequence of the common practice of collapsing these dimensions into a single categorical label. Overall, these findings support the novel view that bilingualism may confer general cognitive benefits associated with specific dimensions of language experience. These findings underscore the need to collect and analyze detailed language and non-language experience data to test the bilingual advantage hypothesis. Additionally, use of statistical methods that account for these nontrivial differences should be considered in order to strengthen confidence in conclusions regarding the effects of bilingualism on executive function.