Difference of perceptual response between auditory stimuli and recalling them

After we keep hearing periodic auditory stimuli, we might be able to recall them like an actual auditory stimulus even if there is no stimulus. The purpose of this study is to clarify the difference of perceptual process between hearing actual auditory stimuli and recalling them by use of EEG. Experiments were carried out to confirm a hypothesis which is that pseudo auditory evoked potentials (AEP) were being observed when the subjects recall the stimuli. It is necessary to use the averaging procedure to enhance P300 which is thought to have strong relationship to perception. Although weak light stimuli were used as triggers of the averaging, the P300 was contaminated by visual evoked potentials (VEP). To solve this problem, the independent component analysis (ICA) was applied to remove the VEPs. In addition, we found an independent component (IC) related to P300. As result of comparison of this IC, no significant difference was observed between hearing and recalling the stimuli. It is probable that these results imply perceptual process in late latency for recalling auditory stimuli is similar to that for hearing actual stimuli.