1. ^* Cognitive Brain Research Unit, Department of Psychology, University of Helsinki, FIN-00014, Finland
2. ^† Department of Phonetics, University of Helsinki, Finland
3. ^‡ BioMag Laboratory, Medical Engineering Centre, Helsinki University Central Hospital, Finland
4. ^§ Department of Applied Physics, Electronics and Information Technology, University of Turku, Finland
5. Acoustics Laboratory, Helsinki University of Technology, Finland
6. ^¶ Department of Psychology, University of Tartu, Estonia

Abstract

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 /õ/) 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 /ö/) relative to when it was a non-prototype (the Estonian /õ/). These phonemic traces, revealed by MMN, are language-specific, as /õ/ 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.