Infant Brain Responses in Auditory Perception: A Review of the Factors Influencing the Polarity of the Mismatch Response

Infant auditory discrimination can be electrophysiologically measured by the mismatch response (MMR) that may either occur with a positive (pMMR) or a negative polarity (nMMR). Infant age has been proposed as the main factor driving MMR polarity, because the pMMR seems to change towards an adult-like nMMR with increasing age. An alternative proposal is that pMMR and nMMR index different underlying processes, and growing evidence suggests that age triggers these processes in concert with other individual and methodological factors differently. The current review assessed influencing factors in the discrimination of speech and non-speech sound contrasts in 0- to 24-month-old typically developing monolingual infants, examining phoneme inventory acquisition as well as general auditory development. Although we found some evidence for an age effect on MMR polarity, this effect could only be interpreted in its interaction with other interindividual, experimental, and data-analysis factors. In sum, our systematic approach disentangling the influencing factors of MMR polarity elucidates the processes underlying pMMR and nMMR and thus informs future study design and data interpretation in the widespread application of the MMR in developmental studies.