On the Average Time- and Frequency-Pattern of Photic Flicker Response in Relation to Intrinsic Alpha Activity Verified by a New Simple Method

Delivering photic flicker stimulations from about 8 to 12 flashes per second for about 60 seconds continuously to relaxed normal adult human subject, the average properties of the driven EEG waves are obtained by applying a new practical crosscorrelation method to eliminate the irrelevant oscillations to the stimulation. The average time-pattern of the intrinsic alpha activity was carved in relief by a new simple autocorrelation method, which is originally demonstrated here. The EEGs are traced from the occipital, parietal, temporal and frontal regions by monopolar technique. Even immediately after the initiation of flicker stimulation, the response wave of the stimulating frequency was driven and tended to build up gradually to the maximum average intensity in the course of contiunal stimulation, especially in the occipital region, showing some fluctuation in size. The average distribution of the driven wave over the scalp was similar to those of the relaxed intrinsic alpha wave activity, in size and phase angle. From these evidences it would be assumed at least for the first approximation that the driven waves are produced from a generator essentially similar to what acts in relaxed state. In the occipital region, the EEG response was easily driven more intensely the intrinsic alpha activity in the relaxed state by a photic flicker stimulation with a higher frequency than that of relaxed alpha activity, whereas weaker response tended to be driven by lower frequency of stimulation. In other regions, however, a reverse tendency was observed immediately after the initiation of the stimulation