PHONETIC INVARIANCE IN THE HUMAN AUDITORY-CORTEX

NEUROMAGNETIC signals evoked by synthesized syllables (/b dipthong ae/ and /g dipthong ae/) were recorded over the left auditory cortex of h ealthy humans. The fundamental frequencies of the syllables varied as if the same speaker had pronounced them at 16 different pitches. Speci fic mismatch responses to infrequent syllables among frequent syllable s of the other type indicated that phonetically invariant information had been extracted at the level of the auditory cortex from the extens ive irrelevant pitch variation. Such a detection mechanism is necessar y for perceiving speech sounds in natural situations with a great deal of acoustic variation present.