Phonetically determined asymmetry of the mismatch negativity in Japanese

The effect of a phonetic category in Japanese on the mismatch negativity (MMN) was examined by using a two-tone “oddball” procedure. One of the stimuli was a phoneme prototype of Japanese [e] and the other, [e/ö], which is perceived by Japanese speakers as showing deviance from typicality but is nonetheless included in the category [e]. In the first session, one of the two stimuli was presented as the standard and the other as the deviant. In the second session, the probability of both stimuli was reversed. As control stimuli, a pair of pure tones (1940 and 1794 Hz) corresponding to the F2 frequencies of [e] and [e/ö], respectively, were presented within the same oddball paradigm. The MMN for deviant [e/ö] revealed greater amplitude and shorter latency than that of deviant [e]. In contrast, there was no significant difference in the amplitude or latency between the pure tones. The results suggest that a phonetic category determines the sensory memory processing in the auditory modality.