Supplementary Material for: The influence of language dominance, type of language and narrative task on speech disfluencies in typically fluent bilingual English-Mandarin children

Introduction Speech disfluencies observed across multiple languages may reflect typical patterns of bilingual development rather than clinical stuttering, prompting a growing need to establish diagnostic criteria to improve the accuracy of stuttering assessment in bilingual individuals. While recent studies have begun to characterise normative disfluency patterns in fluent bilinguals, the manifestation of such disfluencies in languages such as Mandarin remains underexplored. This study investigates the frequency and type of disfluencies in typically developing bilingual children who speak English and Mandarin, and examines how language dominance, language type and narrative task demands influence their disfluency profiles. Method Thirty-six English-Mandarin speaking children comprising 16 balanced bilinguals (Mage = 5.61 years) and 20 English-dominant bilinguals (Mage = 5;56 years) were recruited from various kindergartens. Speech samples were collected across two narrative RETELL tasks (with and without visual guide) and in two languages (English and Mandarin) and were analysed for stuttering-like disfluencies (SLD), non-stuttering-like disfluencies (NSLD) and total disfluencies (TD). Results Approximately 55-65% of the bilingual English-Mandarin children in this study were found to exceed the monolingual diagnostic criteria for SLD, NSLD and TD in at least one speech sample. However, only a subset of children surpassed the thresholds across all measures. Monosyllabic word repetitions and revisions were among the most common SLD and NSLD, respectively. No significant differences in SLD, NSLD and TD were found between English-dominant and balanced bilinguals. While SLD did not appear to be influenced by language or task type, the frequency of NSLD and TD was found to be significantly higher in Mandarin and during narrative RETELL without visual guide. Conclusion The results demonstrate that bilingual children can produce disfluency patterns that are quantitatively and qualitatively different from monolingual and other bilingual populations. Clinically, this highlights the need for bilingual-specific diagnostic frameworks that account for language context, task demands, and different bilingual profiles.