To delineate MMN the ERPs evoked by the standard stimuli are subtracted from the ERPs evoked by the deviant stimuli of the same sequence. This potential, usually peaking at 150–200 ms, can be elicited by any discriminable change in auditory stimulation, reflecting the neural reaction induced by the deviant stimulus in contrast to the sensory memory trace of the preceding stimuli, even in the absence of a person’s attention or in situations of impaired consciousness, i.e. minimal consciousness state and vegetative state.