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.

In general, both consciously and unconsciously perceived stimuli facilitate responses to following similar stimuli. However, masked arrows delay responses to following arrows. This inverse priming has been ascribed to inhibition of premature motor activation, more recently even to special processing of nonconsciously perceived material. Here, inverse priming depended on particular masks, was insensitive to contextual requirements for increased inhibition, and was constant across response speeds. Putative signs of motor inhibition in the electroencephalogram may as well reflect activation of the opposite response. Consequently, rather than profiting from inhibition of primed responses, the alternative response is directly primed by perceptual interactions of primes and masks. Thus there is no need to assume separate pathways for nonconscious and conscious processing.

Human performance may be primed by information not consciously available. Can such priming become so overwhelming that observers cannot help but act accordingly? In the present study, well-visible stimuli were preceded by whole series of unidentifiable stimuli. These series had strong, additive priming effects on behavior. However, their effect depended on the frequency with which they provided information conflicting to the visible main stimuli. Thus, effects of subliminal priming are under observers' strategic control, with the criterion presumably set as a function of the openly observable error frequency. Electrical brain potentials show that this criterion acts simultaneously at the level of visual discrimination of the primes and at motor activation evoked by the primes, thereby shielding observers from unwanted information.