The effect of visual stimuli on the electroencephalogram has been of interest since the earliest work on cerebral potentials. Berger noted changes in alpha rhythm following retinal stimulation. Walker1 and others have studied the effect on the electroencephalogram of intermittent photic stimulation of the retina. The electroencephalogram obtained from the occipital cortex may take on a frequency synchronous with the flicker. This is called photic driving. Moreover, Walker and his associates stated:
... If intermittent photic stimuli are allowed to fall suddenly on the retina, one encounters a peculiar hump and spike arrangement which persists for the first six or eight stimuli, after which the waves assume a more sinusoidal form. This peculiar hump and spike formation may be seen at almost any frequency, but is particularly well demonstrated when the frequency of the intermittent photic stimulus is approximately 6 per second.1
Figure 10 of the paper by Walker