Mismatch responses to pitch changes in early infancy

& We investigated the emergence of discriminative responses to pitch by recording 2-, 3-, and 4-month-old infants ’ electro-encephalogram responses to infrequent pitch changes in piano tones. In all age groups, infants ’ responses to deviant tones were significantly different from responses to standard tones. However, two types of mismatch responses were observed simultaneously in the difference waves. An increase in the left-lateralized positive slow wave was prominent in 2-month-olds, present in 3-month-olds, but insignificant in 4-month-olds. A faster adultlike mismatch negativity (MMN), lateralized to the right hemisphere, emerged at 2 months of age and became earlier and stronger as age increased. The coexistence and dis-sociation of two types of mismatch responses suggests different underlying neuromechanisms for the two responses. Further-more, the earlier emergence of the MMN-like component to changes in pitch compared to other sound features implies that neural circuits involved in generating MMN-like responses have different maturational timetables for different sound features. &amp