AUTOMATIC DISCRIMINATION OF PHONETICALLY RELEVANT AND IRRELEVANT VOWEL PARAMETERS AS REFLECTED BY MISMATCH NEGATIVITY

An auditory event-related brain potential called mismatch negativity ( MMN) was measured to study the perception of vowel pitch and formant f requency. In the MMN paradigm, deviant vowels differed from the standa rds either in F0 or F2 with equal relative steps. Pure tones of corres ponding frequencies were used as control stimuli. The results indicate that the changes in F0 or F2 of vowels significantly affected the MMN amplitudes. The only variable significantly affecting the MMN latenci es was sex which, however, did not have any effect on the amplitudes o f the MMN. As expected, the MMN amplitudes increased with an increase in the acoustical difference between the standards and the deviants in all cases. On the average, the amplitudes were lower for the vowels t han for the pure tones of equal loudness. However, in vowels, minor fr equency changes in F0 produced higher MMN amplitudes than similar rela tive changes in F2. It was also noted that even the smallest and phone tically irrelevant change in F2 was detected by the MMN process. In ov erall, the results demonstrate that the MMN can be measured separately for F0 and F2 of vowels, although the MMN responses show large interi ndividual differences.