Influence of red light and pattern on photic driving.

The photic drivings (PDs) in response to the following visual stimuli were studied in 108 cases, of which 84 (78%) were epileptics; ages ranged from 5 to 57 years old. An intermittent photic stimulation (IPS) of 5 cycles/sec by a stroboscopic light was given to the subjects with eyes closed and open. Following these stimuli, red-flicker and flickering-pattern of 5 cycles/sec and 20 cd/m2 were given successively to the subjects with eyes open using a "visual stimulator". The PDs evoked by IPS to the eyes closed and those by red-flicker were similar in the wave form and amplitude. In most of the cases, however, both stimuli failed to evoke apparent PDs (over 25 muV in amplitude), i.e., in 81% and 72%, respectively. IPS to the eyes open and flickering-pattern showed comparable effects in evoking PDs; they evoked high amplitude PDs (over 50 muV in amplitude) with a frequency of 19% by the former and 28% by the latter. In 95 out of 108 cases, both IPS to the eyes closed and red-flicker failed to evoke apparent PDs. In rare cases, IPS to eyes closed evoked high amplitude PDs; in 7 out of these 8 cases, red-flicker also evoked high amplitude PDs. In 18 out of 20 cases in which high amplitude PDs were evoked by IPS to the eyes open, flickering-pattern was also effective in evoking high amplitude PDs. Based on these findings, similarities between IPS to the eyes closed and red-flicker, and similarities between IPS to the eyes open and flickering-pattern in evoking PDs are discussed. It is concluded that flickering-pattern and red-flicker are superior to IPS to the eyes open and closed, respectively, for examining the low frequency PDs.