Neural attunement processes in infants during the acquisition of a language-specific phonemic contrast.
To elucidate the developmental neural attunement process in the language-specific phonemic repertoire, cerebral hemodynamic responses to a Japanese durational vowel contrast were measured in Japanese infants using near-infrared spectroscopy. Because only relative durational information distinguishes this particular vowel contrast, both first and second language learners have difficulties in acquiring this phonemically crucial durational difference. Previous cross-linguistic studies conducted on adults showed that phoneme-specific, left-dominant neural responses were observed only for native Japanese listeners. Using the same stimuli, we show that a larger response to the across-category changes than to the within-category changes occurred transiently in the 6- to 7-month-old group before stabilizing in the groups older than 12 months. However, the left dominance of the phoneme-specific response in the auditory area was observed only in the groups of 13 months and above. Thus, the durational phonemic contrast is most likely processed first by a generic auditory circuit at 6-7 months as a result of early auditory experience. The neural processing of the contrast is then switched over to a more linguistic circuit after 12 months, this time with a left dominance similar to native adult listeners.
Minagawa-Kawai
Yasuyo
Y
Department of Psychology, Keio University, Tokyo 108-8345, Japan. myasuyo@bea.hi-ho.ne.jp
Mori
Koichi
K
Naoi
Nozomi
N
Kojima
Shozo
S
D000161:Acoustic Stimulation / Q000379:methods*; D002540:Cerebral Cortex / Q000502:physiology; D002675:Child, Preschool; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007223:Infant; D007804:Language Development; D008297:Male; D013067:Speech Perception / Q000502:physiology*; D013997:Time Factors