P3 (or P300), a positive component occurring from 300 to 500 msec after a stimulus, reflects “stimulus significance” (e.g., task relevance, unpredictability, and motivational factors). To elicit P3, researchers generally use oddball tasks in which rarely occurring target stimuli (i.e., oddballs) are interspersed among frequently occurring nontarget stimuli. In normal subjects, frequently occurring nontarget stimuli elicit N1’s but not P3’s, whereas oddball stimuli elicit both N1’s and P3’s.
