Speech sound learning depends on individuals' ability, not just experience.

Abstract

The goal of this study was to investigate if phonetic experience with two languages facilitated the learning of novel speech sounds or if general perceptual abilities independent of bilingualism played a role in this learning. The underlying neural mechanisms involved in novel speech sound learning were observed in groups of English monolinguals (n = 20), early Spanish-English bilinguals (n = 24), and experimentally derived subgroups of individuals with advanced ability to learn novel speech sound contrasts (ALs, n = 28) and individuals with non-advanced ability to learn novel speech sound contrasts (non-ALs, n = 16). Subjects participated in four consecutive sessions of phonetic training in which they listened to novel speech sounds embedded in Hungarian pseudowords. Participants completed two fMRI sessions, one before training and another one after training. While in the scanner, participants passively listened to the speech stimuli presented during training. A repeated measures behavioral analysis and ANOVA for fMRI data were conducted to investigate learning after training. The results showed that bilinguals did not significantly differ from monolinguals in the learning of novel sounds behaviorally. Instead, the behavioral results revealed that regardless of language group (monolingual or bilingual), ALs were better at discriminating pseudowords throughout the training than non-ALs. Neurally, region of interest (ROI) analysis showed increased activity in the superior temporal gyrus (STG) bilaterally in ALs relative to non-ALs after training. Bilinguals also showed greater STG activity than monolinguals. Extracted values from ROIs entered into a 2×2 MANOVA showed a main effect of performance, demonstrating that individual ability exerts a significant effect on learning novel speech sounds. In fact, advanced ability to learn novel speech sound contrasts appears to play a more significant role in speech sound learning than experience with two phonological systems.