. Tohoku J. exp. Med., 1988, 156 (2), 165-173 -Power spectrum of photic driving elicited by 5/sec flickering dot pattern (FDP) and 5/sec red flicker (RF) stimuli was investigated in 137 psychiatric outpatients. They consisted of 61 adults (33 males and 28 females) from 20 to 44 years of age, 55 preseniles (25 males and 30 females) from 45 to 64 years and 21 seniles (9 males and 12 females) over 65 years of age. Powers of 5 and 10/sec photic driving elicited by FDP and RF stimuli were greater than those of the other higher harmonics and increased significantly with age. When such a finding was compared in relation to gender, significant increase of power with age was found for 5 and 10/sec photic driving elicited by both stimuli in females, whereas it was found only for 5/sec photic driving elicited by RF stimulation in males. Our findings suggest that the visual system of older female patients is very responsive not only to patterned stimuli but also to red flicker stimulation. photic driving ; geometric pattern ; red color ; aging; gender Within a span of four decades since the first report by Walter et al. (1946) appeared, intermittent photic stimulation by the use of stroboscopic white light (to be abbreviated as IPS, hereafter) has been the most common method for eliciting photic driving in a routine EEG examination.Studies dealing with the activation of photoconvulsive response have revealed that visual simuli of flickering geometric pattern (Jeavons et al. 1972;Engel 1974;Panayiotopoulos 1974;Takahashi and Tsukahara 1975) and red flicker (Carterette and Symmes 1952;Takahashi and Tsukahara 1976) were more effective in provoking photoconvulsive response than IPS. Application of flickering dot pattern and red flicker stimuli