Mismatch Negativity - Characteristics


The MMN is a response to a deviant within a sequence of otherwise regular stimuli; thus, in an experimental setting, it is produced when stimuli are presented in a many-to-one ratio; for example, in a sequence of sounds s s s s s s s d s s s s d s s s..., the d is the deviant or oddball stimulus, and will elicit an MMN response. The mismatch negativity occurs even if the subject is not consciously paying attention to the stimuli. Processing of sensory stimulus features is essential for humans in determining their responses and actions. If behaviourally relevant aspects of the environment are not correctly represented in the brain, then the organism's behaviour cannot be appropriate. Without these representations our ability to understand spoken language, for example, would be seriously impaired. Cognitive neuroscience has consequently emphasised the importance of understanding brain mechanisms of sensory information processing, that is, the sensory prerequisites of cognition. Most of the data obtained, unfortunately, do not allow the objective measurement of the accuracy of these stimulus representations (see Näätänen, 1992). In audition, recent cognitive neuroscience seems to have succeeded in extracting such a measure, however. This is the mismatch negativity (MMN), a component of the event-related potential (ERP), first reported by Näätänen, Gaillard, and Mäntysalo (1978). An in-depth review of MMN research can be found in Näätänen (1992) while other recent reviews also provide information on the generator mechanisms of MMN (Alho 1995), its magnetic counterpart, MMNm (Näätänen, Ilmoniemi & Alho, 1994), and its clinical applicability (Näätänen & Alho, 1995).

The auditory MMN can occur in response to deviance in pitch, intensity, or duration. The auditory MMN is a fronto-central negative potential with sources in the primary and non-primary auditory cortex and a typical latency of 150-250 ms after the onset of the deviant stimulus. Sources could also include one from the right opercular part of the inferior frontal gyrus. The amplitude and latency of the MMN is related to how different the deviant stimulus is from the standard. Large deviances elicit MMN at earlier latencies. For very large deviances, the MMN can even overlap the N100 (e.g., Campbell et al., 2007).

The visual MMN can occur in response to deviance in such aspects as color, size, or duration. The visual MMN is an occipital negative potential with sources in the primary visual cortex and a typical latency of 150-250 ms after the onset of the deviant stimulus.

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