Physiological indices of bilingualism: Oral-motor coordination and speech rate in Bengali-English speakers

Purpose: To examine how age of immersion and proficiency in a 2nd language influence speech movement variability and speaking rate in both a 1st language and a 2nd language. Method: A group of 21 Bengali-English bilingual speakers participated. Lip and jaw movements were recorded. For all 21 speakers, lip movement variability was assessed based on productions of Bengali (L1; 1st language) and English (L2; 2nd language) sentences. For analyses related to the influence of L2 proficiency on speech production processes, participants were sorted into low-(n = 7) and high-proficiency (n = 7) groups. Lip movement variability and speech rate were evaluated for both of these groups across L1 and L2 sentences. Results: Surprisingly, adult bilingual speakers produced equally consistent speech movement patterns in their production of L1 and L2. When groups were sorted according to proficiency, highly proficient speakers were marginally more variable in their L1. In addition, there were some phoneme-specific effects, most markedly that segments not shared by both languages were treated differently in production. Consistent with previous studies, movement durations were longer for less proficient speakers in both L1 and L2. Interpretation: In contrast to those of child learners, the speech motor systems of adult L2 speakers show a high degree of consistency. Such lack of variability presumably contributes to protracted difficulties with acquiring nativelike pronunciation in L2. The proficiency results suggest bidirectional interactions across L1 and L2, which is consistent with hypotheses regarding interference and the sharing of phonological space. A slower speech rate in less proficient speakers implies that there are increased task demands on speech production processes.