Phonetic learning abilities : behavioral, neural functional, and neural anatomical correlates

• Main Author: Golestani, Narly A.
• Other Authors: Zatorre, Robert J. (advisor)
• Format: Others
• Language: en
• Published: McGill University 2001
• Subjects: Speech perception; Second language acquisition > Physiological aspects; Neurolinguistics
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38196

The studies included in this thesis had as aim to elucidate how individual differences in phonetic learning abilities might be related to differences in more general, psychoacoustic learning abilities, and in how they might be related to differences in brain function and brain morphology. === We tested and trained English speaking volunteers to perceive the Hindi dental-retroflex phonetic contrast. We found evidence suggesting that the ability to accurately perceive "difficult" non-native contrasts is not permanently lost during development. We also tested and trained subjects to perceive the difference between non-linguistic rapidly changing and steady-state tonal sounds, and found evidence supporting the hypothesis that successful phonetic learning is in part a function of a more general psychoacoustic ability to process rapidly changing sounds. === The aim of the second study was to determine how the pattern of brain activity may change as a result of training with non-native speech sounds, and in whether it is possible to differentiate "learners" from "non-learners" on the basis of neural activation patterns. Results of this functional magnetic resonance imaging (fMRI) investigation suggested that successful learning of a non-native contrast results in the recruitment of the same areas that are involved in the processing of native contrasts; but the degree of success in learning is accompanied by more efficient neural processing in classical frontal speech regions, while making greater processing demands in left parieto-temporal speech regions. === In the final study, we correlated phonetic learning measures with brain morphology throughout the whole brain volume. We found evidence for overall larger parietal volumes in the left relative to the right hemisphere, and for more white relative to gray matter in the left hemisphere in the learners and not in the nonlearners. This finding is consistent with findings by other investigators suggesting that left-hemispheric dominance for speech may be in part accounted for by hemispheric differences in white matter connectivity, which may allow faster intra- and inter-hemispheric neural transmission. This latter feature may be critical for the processing of consonant speech sounds, which depends on the ability to process sounds that change on the time scale of 30--50 milliseconds.