In virtually all tasks used in experimental psychology, stimuli evoke a P3 component when EEG is recorded. Therefore, understanding this component might promote understanding about how human brains generally organize behavior control in such tasks. In intracranial recordings, correlates of scalp-recorded P3 have been found at various locations, both at subcortical (hippocampus, thalamus, basal ganglia) and cortical sites (superior parietal and frontal lobe). Therefore, P3 might have some integrative function.
The present study tests whether P3 reflects the link between perceptual processing and response preparation. If indeed equally related to both processes, P3 should not be smaller in response-locked than in stimulus-locked averages. To this end, data were analyzed from two different tasks and evoked by visual and auditory stimuli.
Parietal P3 amplitudes were indeed not smaller in response-locked than in stimulus-locked averages, in some instances even larger. For comparison, peak amplitudes both of lateralized readiness potentials and of response-force were larger when response-locked (as could be expected) and fronto-central P3 with auditory stimuli was larger when stimulus-locked (as could be generally expected for P3 if it were stimulus-related only).
Thus, parietal P3 seems unique in being equally related to stimulus and response. It might reflect fast-track decision, based on prepared S-R links. The modules needed for this process are described and are mapped to neurophysiological evidence about P3.