A PASSIVE EVENT-RELATED POTENTIAL

Event potentials (ERPs) were recorded in response to visual patterns i n two conditions: (1) where no instructions were given to subjects; an d (2) where subjects pressed a button whenever a rare stimulus was det ected. P3 amplitudes for the No Instructions condition were smaller th an for the Active condition, but the latency of the P3s did not differ across conditions. In both conditions, the P3 was either absent or si gnificantly smaller for frequent stimuli than for rare stimuli. It app ears a 'passive' visual P3 is measurable, and it occurs at the same la tency as a P3 recorded in association with an active response. Thus, i t may be possible to record P3s in response to visual stimulation in s ubjects who cannot follow instructions to respond to rare events. (C) 1998 Elsevier Science B.V.