Potential contamination effects of neuronal refractoriness on the speech-evoked mismatch negativity response.

The mismatch negativity response (MMN) is an event-related potential that is believed to reflect the automatic (possibly preconscious) neural processing of changes in ongoing environmental sounds. The MMN involves a negative voltage shift of baseline electroencephalographic (EEG) activity in the approximate latency window of the N1 and P2 cortical potentials in response to new or novel sounds. The most commonly used laboratory tests for extracting the MMN from EEG activity all involve oddball stimulus presentation procedures in which the interstimulus intervals (ISIs) of the frequently occurring standard sounds are shorter in length then that of the infrequently occurring deviant sounds. This presents the possibility that the MMN response could be affected by neuronal refractory or recovery events. The present study tested 12 young females, using the syllabic events /da/ and /ga/ as standard and deviant stimuli, and found evidence that, with certain experimental protocols, ISI-dependent neural refractory effects can affect the morphology of the MMN, possibly resulting in misinterpretation of the underlying neural bases of the response.