Separability of different negative components of the event-related potential associated with auditory stimulus processing

The lateral scalp distribution of the early negative selective-attention effect on auditory event-related potentials (ERPs) was compared to the distribution of the midline-negative N1 component inverting in polarity at the scalp area below the Sylvian fissure. No such polarity inversion was observed for the selective-attention effect at the N1 latency. This result supports the proposal that another component, the processing negativity (PN), overlaps (summates to) the exogenous N1 in the ERPs to attended stimuli. A subsequent experiment demonstrated that the mismatch negativity (MMN: peaking at 150-200 ms), an ERP component automatically elicited by deviant stimuli presented among homogenous repetitive stimuli, had opposite polarities above and below the Sylvian fissure. Thus, the MMN at least partly emanates from a cerebral generator which considerably overlaps that of the N1. The results are discussed in terms of separability of the brain mechanisms involved in the voluntary and involuntary processing of auditory stimuli reflected by the PN and MMN, respectively.