Anatomical correlates of foreign speech sound production.

Previous work has shown a relationship between brain anatomy and how quickly adults learn to perceive foreign speech sounds. Faster learners have greater asymmetry (left>right) in parietal lobe white matter (WM) volumes and larger WM volumes of left Heschl's gyrus than slower learners. Here, we tested native French speakers who were previously scanned using high-resolution anatomical magnetic resonance imaging. We asked them to pronounce a Persian consonant that does not exist in French but which can easily be distinguished from French speech sounds, the voiced uvular stop. Two judges scored the goodness of the utterances. Voxel-based morphometry revealed that individuals who more accurately pronounce the foreign sound have higher WM density in the left insula/prefrontal cortex and in the inferior parietal cortices bilaterally compared with poorer producers. Results suggest that WM anatomy in brain regions previously implicated in articulation and phonological working memory, or the size/shape of these or adjacent regions, is in part predictive of the accuracy of speech sound pronunciation.