When, How, and for Whom? A narrative review contextualizing bilingual effects in ADHD

Attention-Deficit/Hyperactivity Disorder (ADHD) is one of the most common neurodevelopmental disorders, characterized by symptoms of (i) inattention, (ii) hyperactivity-impulsivity or (iii) both. Atypical patterns of attention are a common phenotype in this population. To date, research on bilingualism in ADHD has not reached a consensus regarding the impact of bilingualism on executive functions (EFs) and ADHD-related behavior. This review focuses primarily on bilingualism in ADHD and highlights how outcomes within the ADHD literature, considering child, adolescent and adult populations, may vary systematically according to contextual moderators. First, socioeconomic status (SES) should be carefully controlled for, as it independently affects EFs, receptive vocabulary and attention abilities. Second, detailed profiling of language background is required to better interpret reaction time and accuracy findings, allowing performance differences to be linked to variables such as context of language usage, frequency of use, or number of languages acquired. Furthermore, implementation of tools such as the Q-BEx and LEAP-Q questionnaires is encouraged to precisely profile one's language background and capture language-experience variables, thus clarifying the role of bilingualism in cognitive performance in ADHD. Third, linguistic distance (LD) potentially imposes dynamic effects on EFs for bilinguals with ADHD with the literature showing bilingual advantages in EFs given one's proficiency and distance between languages. Co-occurring Autism Spectrum Disorder (ASD) is acknowledged given the comorbidity's prevalence rates in ADHD groups, as well as the fact that it has been associated with additional challenges in language and/or social skills. For future research, hypotheses regarding effects of bilingualism in ADHD groups with comorbid ASD are presented. Additionally, the incorporation of longitudinal studies in bilingual ADHD research is emphasized given that cross-sectional study designs can overlook outcomes related to EFs or ADHD-related behavior and diagnosis at different developmental time-points. Together, these insights call for a shift from global comparisons toward context-sensitive approaches that capture the diversity of bilingual experience in ADHD.