Language-specific phoneme representations revealed by electric and magnetic brain responses

There is considerable debate about whether the early processing of sounds depends on whether they form part of speech. Proponents of such speech specificity postulate the existence of language-dependent memory traces, which are activated in the processing of speech(1-3) but not when equally complex, acoustic non-speech stimuli are processed. Here we report the existence of these traces in the human brain, We presented to Finnish subjects the Finnish phoneme prototype /e/ as the frequent stimulus, and other Finnish phoneme prototypes or a non-prototype (the Estonian prototype /(o) over tilde/) as the infrequent stimulus. We found that the brain's automatic change-detection response, reflected electrically as the mismatch negativity (MMN)(4-10), was enhanced when the infrequent, deviant stimulus was a prototype (the Finnish /o/) relative to when it was a non-prototype (the Estonian /(o) over tilde/). These phonemic traces, revealed by MMN, are language-specific, as /(o) over tilde/ caused enhancement of MMN in Estonians. Whole-head magnetic recordings(11,12) located the source of this native-language, phoneme-related response enhancement, and thus the language-specific memory traces, in the auditory cortex of the left hemisphere.