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Abstract

Hypotheses about the P3 component of the event-related EEG potential have usually assumed that P3b reflects some processing independent from organizing the response. In contrast, the notion that P3b is related to a decision process implies some mediating function between stimulus and response. If P3b does indeed reflect the link between perceptual processing and response preparation (1) amplitudes should be as large in response-locked averages as in stimulus-locked averages, (2) this should be true independent of response speed, for separate subaverages of slow and fast responses, and (3) latencies should vary across response speed both in stimulus-locked and in response-locked averages. These hypotheses were tested in data evoked by visual and auditory stimuli in choice-response tasks. All three predictions were confirmed. In contrast to this balanced relation to perception and responding, fronto-central P3 with auditory stimuli was stimulus-related and, for comparison, the peak amplitudes of both the response-force and of the lateralized readiness potential were response-related. We conclude that P3b reflects a process that mediates between perceptual analysis and response initiation, possibly monitoring whether the decision to classify some stimulus is appropriately transformed into action.