Abstract 1. 1. A method of producing photic stimulation by means of a periodically altered pattern is presented to be used with EEG investigations. 2. 2. This method circumvents the more bothersome artifacts occasioned in the use of the standard strobe light. 3. 3. The “pattern driving effect” may be easily observed in the occipital leads even with “just discernable” pattern illumination. This occurs at light levels below which “on-off” stimulation can be detected. 4. 4. The method is easily applicable to experimental procedures though there is no evidence to date that it could be used to trigger epileptic discharges.