Endogenous potentials evoked in simple cognitive tasks: scalp topography.

The scalp topography of endogeneous potentials was studied during a series of simple cognitive tasks in the auditory modality. P3 and Slow Wave showed the expected task correlates of being larger to rare than to frequent tones, and larger when attended than ignored, but N2 was not clearly measurable due to overlap with P2 and P3. Overall, across all task conditions, P3 was larger at sites over the right hemisphere than the left, particularly for sites near the midline (F3, F4, C3, C4, P3, P4). P3 was present (though smaller) to rare omitted stimuli in a tone series, as well as to tones presented at long, random intervals (3 to 9 s) in a simple counting task. P3 was very large to novel, unique, nontarget auditory stimuli, and had a somewhat different distribution to these stimuli than to targets, suggesting a difference in the underlying intracranial generators. Except for these novel nontarget sounds, P3 showed a consistent topography across tasks in spite of differences in amplitude.