The effects of English (L2) language proficiency on speech motor indices for bisyllabic bilabial word utterances in typical Kannada (L1)-English (L2) bilinguals

Objectives: The study examined the influence of second language proficiency on intra-articulatory and inter-articulatory speech motor variability measures for bilabial bisyllabic words in typical Kannada (L1)-English (L2) bilinguals. Methods: Sixteen typical Kannada English bilingual adults were categorized into high and low L2 proficiency groups (n=8 each) participated in a task of repeating a bilabial bisyllabic word pair matched for syllable structure, syllable length and duration. To understand the intra-articulatory and inter-articulatory stability, Spatiotemporal Index (STI) of Lower Lip (LL) and Lip Aperture Variability (LAVAR) measures were computed respectively. A mixed language paradigm was used where the word pairs of L1 and L2 were randomly mixed and presented to the participants. Results: Analysis of STI of LL revealed comparable movement stability across languages and the influence of L2 language proficiency was found to be insignificant. However, LAVAR revealed language specific differences wherein L1 was more variable than L2. Further, LAVAR was found to be independent of L2 language proficiency, possibly suggesting a language invariant speech motor plan operating at the intra-articulatory level but a language sensitive speech motor plan functioning at the inter-articulatory stability measure in a word context. Conclusion: The findings did not support the influence of L2 language proficiency on STI and LAVAR measures in a word context. The study concluded with a possible scope of utilizing mixed language paradigm in speech motor control studies addressing speech motor stability in bilinguals.