The present study examined cerebral representations of Japanese long and short vowel categories with near-infrared spectroscopy (NIRS) by measuring the hemodynamic changes. Results showed that NIRS could capture phoneme-specific information. The left side of the auditory area showed large hemodynamic changes only for contrasting stimuli between which the phonemic boundary was estimated, but not for stimuli differing by an equal duration but belonging to the same phoneme category. Left dominance in phoneme processing was also confirmed for the across-category stimuli. These findings indicate that the Japanese vowel contrast based only on duration differences is dealt with in the same language-dominant hemisphere as other spectrally varying phonemic categories, and that the cortical activities related to its processing can be detected with NIRS.
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