Neural Underpinnings of Early Speech Perception and Emergent Literacy.

Mismatch negativity (MMN) is an event-related potential component used to index automatic auditory change detection. Thus, MMN provides an excellent tool to assess the speech sensitivity of infants and children. Although MMN is well established in adults, the polarity and latency of mismatch responses (MMRs) in infants are highly inconsistent across studies. This paper aims to provide a comprehensive review of MMN studies of speech perception in early infancy. In particular, data from a series of MMN studies of Mandarin lexical tone, vowels, and initial consonants will be presented to demonstrate how phonological saliency, size of deviance, and neural maturation modulate MMRs in early infancy. These data suggest that MMN and positive MMRs index different functional characteristics and may provide information on when and how children's speech perception becomes automatic at different developmental stages. By using MMN to index sensitivity to speech discrimination, dyslexic children usually show reduced or absent MMN, which supports the relationship between phonological sensitivity and literacy. However, children with attention deficit/hyperactivity disorder showed the typical MMN, but attenuated P3a and enhanced late discriminative negativity. Taken together, the MMR characteristics, including amplitude, peak latency, and the transition of polarity, may be used to index the maturation of speech development and for the early identification of children with atypical language development.