The ERP task most commonly used to elicit the P3 is the so-called “odd-ball” task, in which rare “oddball” stimuli are embedded in a series of frequent stimuli (standards or nontargets). For example, in an auditory task, the subject listens to frequent “boops” and rare “beeps” in a random stream of tone bursts. If the subject is asked to attend or respond to the rare “beep” stimulus, it is designated as a target; the P3s recorded in response to these task-relevant targets are largest posteriorly on the scalp (over the parietal region [figure 1]) and are designated as P3b components. If the subject is not asked to attend to rare “beep” stimuli, P3s recorded to these unattended rare nontarget stimuli in a repetitive background have a more frontal distribution and are designated as P3a (figure 1); although rare nontargets elicit these P3as, frequent nontargets usually do not elicit any P3s.
