Abstract
The relation between a stimulus and a P300 component was investigated using a single stimulus paradigm and a compound stimulus paradigm. The single stimulus paradigm was designed to assess the relation between the intertarget interval (ITI) and the P300 component for an ITI of 3-10s. When the ITI was set long, P300 amplitude tended to increase. The change in P300 amplitude of an auditory evoked potential (AEP) was greater than that of a visual evoked potential (VEP), suggesting that the P300 of AEPs is more sensitive to the ITI. The compound stimulus paradigm was designed to examine the P300 component when two kinds of sensory stimuli (visual and auditory) were presented. Interstimulus intervals (ISIs) between the two different stimuli and between the same stimuli were set at five and ten seconds, respectively. The cumulative averaged waveforms showed a decreasing amplitude of event-related potentials in the following order: a single target was set and consistent with the corresponding sensory stimulus; both targets were set and each target was consistent with a sensory stimulus; a single target was set and each target was inconsistent with a sensory stimulus; and no target was set. In the compound stimulus paradigm, the VEP amplitude varied markedly with the target stimulus. The results suggest that VEPs are sensitive to the stimulus modality.
