Analysis of speech sounds is left-hemisphere predominant at 100-150 ms after sound onset

HEMISPHERIC specialization of human speech processing has been found in bra in imaging studies using fMRI and PET. Due to the restricted time resolutio n, these methods cannot, however, determine the stage of auditory processin g at which this specialization first emerges. We used a dense electrode arr ay covering the whole scalp to record the mismatch negativity (MMN), an eve nt-related brain potential (ERP) automatically elicited by occasional chang es in sounds, which ranged from non-phonetic (tones) to phonetic (vowels). MMN can be used to probe auditory central processing on a millisecond scale with no attention-dependent task requirements. Our results indicate that s peech processing occurs predominantly in the left hemisphere at the early, pre-attentive level of auditory analysis. NeuroReport 10:1113-1117 (C) 1999 Lippincott Williams & Wilkins.