The T-complex responses to lexical tone in bilingual children with Mandarin-English and Spanish-English backgrounds

Individuals with various developmental disorders, including auditory processing disorders, often show abnormalities in cortical auditory evoked potentials (CAEPs) at temporal sites. Temporal CAEPs, or the T-complex, have been studied in monolingual and bilingual children with non-tonal languages, but the developmental trajectory of the T-complex in bilingual children with tonal languages, like Mandarin-English, remains largely unexplored. This study aims to examine neurodevelopmental changes in Mandarin lexical tone processing, reflected in the T-complex, in children from Mandarin-English and Spanish-English backgrounds. We also examined how different bilingual experience influences the T-complex responses. We used a multiple oddball paradigm and recorded event-related potentials from bilingual Mandarin-English adults and children aged 5–10 from Mandarin-English and Spanish-English households, employing 65 sensors. Tone 1 (high-level tone) and Tone 2 (low-rising tone) were the deviant/infrequent tones, while Tone 3 (low dipping tone) served as the standard/frequent tones. T-complex was analyzed using the standard tone (Tone 3). Our results show that bilingual language experience and age-related brain maturation influence the T-complex. In children 5–10 years old, both lexical tone exposure and increasing age led to more distinct T-complex formation, suggesting that the developmental trajectory of the T-complex is prolonged.