Information processing to rare and frequent warning stimuli in a C.N.V. paradigm

Seven normal young men were submitted to standard and target paired auditory stimuli. The warning stimulus of paired tones informed subjects whether or not the impending unconditional stimulus implied a motor response. Subjects were instructed to execute the motor response at less one second after the unconditional stimulus occurrence, and were informed that the standard warning stimulus was always followed by an additional stimulus which confirmed its detection. Components of target warning and imperative stimuli responses presented a significant increase in amplitude with regard to evoked potential components elicited by standard warning and unconditional tones. P3 waves observed in response to standard warning and unconditional stimuli culminated over fronto-central cortex, while P3 of target warning and imperative tone responses peaked over centro-parietal cortex. These results suggest that manipulating warning stimulus significance by assigning to it a discriminative function, can modify processing of the information carried out by paired stimuli.