The masking effect in foreign speech sounds perception revealed by neuromagnetic responses

The backward masking effect on non-native consonants by a following vowel was examined using neuromagnetic responses to synthesized speech sounds. Native speakers of Japanese were presented with sequences of frequent (85%) and infrequent (15%) speech sounds (/ra/ and /la/ respectively, no /l/ /r/ contrast in Japanese language). The duration of the stimuli was 110 ms in a short session and 150 ms in a long session. In the short session, the stimuli were terminated in the course of the transition from the consonant to the vowel to diminish the masking effect from the vowel part. A distinct magnetic counterpart of mismatch negativity (MMNm) was observed for the short session, whereas a smaller MMNm was observed for the long session.