Mismatch negativity (MMN) as an index of central auditory system plasticity.

The mismatch negativity (MMN) is an electric brain response which is automatically elicited by any discriminable change in a repetitive sound or sound pattern. When this change is made smaller in magnitude, the MMN is attenuated in amplitude, eventually vanishing at around the discrimination threshold. Therefore the MMN provides a unique objective index for a subject or patient's discrimination accuracy. Furthermore, with the MMN, these discrimination thresholds can be separately determined for all the different auditory attributes. Moreover, the individual's ability to discriminate complex sound stimuli and patterns such as different phonemes can also be measured by using the MMN.