On the relationship of P3a and the Novelty-P3

Deviant stimuli give rise to a late positive ERP component with latencies f rom 250 to 400 ms. Target deviants elicit a P300 with maximum amplitude ove r parieto-central recording sites while the 'P300' elicited by deviant nont arget stimuli occurs somewhat earlier and shows a more frontally-oriented s calp distribution. Two varieties of frontal P300s have been described, elic ited either by rare stimuli (target or nontarget) presented in a two-stimul us oddball task (P3a) or by infrequent, unrecognizable stimuli presented in the context of a three-stimulus oddball task (Novelty-P3). The Novelty-P3 has been observed in a number of subsequent studies; the P3a has not been e xtensively studied and both its significance and existence have been called into question. The present report describes a replication of two prototypi cal studies with 'frontal' P3s observed in each context. Application of fac tor analysis to the two sets of ERP waveforms does not support a distinctio n between these two components. (C) 2001 Elsevier Science B.V. All rights r eserved.