Neuroanatomical markers of individual differences in native and non-native vowel perception

Although most human beings experience no difficulty in perceiving their native language, strong individual differences are observed for certain foreign phonemic contrasts. Diaz, Baus, Escera, Costa, and Sebastian-Galles (2008, Brain potentials to native phoneme discrimination reveal the origin of individual differences in learning the sounds of a second language. Proceedings of the National Academy of Sciences of the United States of America, 105, 16083–16088) reported a correlation between event-related potential (ERP) responses to native and non-native vowels in a group of early and highly-skilled bilinguals. In the present study, we compared the brain morphology of two groups of bilinguals who were equally proficient in their second language but differed in their perception of both native and non-native vowels. A whole brain, voxel-based morphometry analysis (VBM) revealed larger white matter volume in the right insulo/fronto-opercular region in individuals who exhibited poorer perceptual discrimination of native and non-native vowels. As the volume of the left Heschl’s gyri has previously been shown to correlate with the ability to perceive foreign phonemic contrasts (between consonants), we also measured the white and grey matter volumes of Heschl’s gyri in our subjects. We did not observe any significant relation between these volumes and vowel discrimination capabilities. This result allows the identification of anatomical brain differences related to individual differences in vowel perception. The present results add to the relatively unexplored area of the relationship between brain structure and language function in adult healthy population.

► Individual differences in vowel perception are correlated with white-matter differences in right fronto-opercular areas. ► Native and non-native abilities in vowel perception are paralleled with differences in the right frontal operculum. ► Vowel perception difficulties are not corresponded with differences in the anatomy of the HG.