Different trajectories for becoming bilingual lead to comparable outcomes in cognitive flexibility

Aims and Objective: Bilingualism has been proposed to affect cognitive flexibility, but findings in the literature are mixed. One reason for this might be the different trajectories of how participants acquired the second language, either through immersion or formal education. The present study investigates differences and commonalities of becoming bilingual depending on trajectory. Methodology: To assess cognitive flexibility, participants completed a task-switching and a language-switching paradigm, which were well-matched to each other. Language capabilities were assessed by self-report, objective fluency measures, and balance quotients. We assessed participants of five bilingual populations who together spoke five different languages. Data and Analysis: We analyzed global mixing costs, reflecting proactive language and task control, as well as local switch costs, reflecting reactive language and task control processes. The impact of language capabilities on mixing costs was assessed using linear mixed models. We also report correlations among language capability measures, sociodemographic variables, and working memory. Findings: We observed reliable mixing costs but no switch costs. Task and language mixing costs were smaller in participants who had a later age of L2 onset and higher L2 phonemic fluency, namely those who followed the formal education path to bilingualism. L2 phonemic fluency was the most consistent predictor for overall performance speed and reduced mixing costs. Originality: Using three different study sites and participants differing in their trajectory of becoming bilingual, this study provides a more diverse picture than many previous studies. Furthermore, using small language populations, the study shows the benefits of language fluency measures that are widely available. Significance and Implications: The present study bolsters the conceptualization of bilingualism as a multifaceted experience. Nonetheless, in the current study, bilingualism led to comparable outcomes in cognitive flexibility. Finally, measuring language capabilities should carefully consider cognitive processes not related to language that could explain variability in performance.