Photoparoxysmal response elicited by flickering dot pattern stimulation to the center and periphery

Objective: We performed this study to elucidate the roles of stimulus spatial frequency and visual field in eliciting generalized photoparoxysmal response (PPR) by flickering dot pattern (FDP) stimulation. Methods: We studied 20 photosensitive epilepsy patients, aged 7–48 years (means±SD, 21.4±11.7 years), producing a 20 Hz FDP stimulation with a strobo-filter. Using dot patterns (0.5, 1, 2, 4 and 6 mm in diameter), we gave FDP stimulation to the center (11×11°) and periphery (11–30×11–30°) of subjects with eyes open, and analyzed each PPR appearance latency. Results: Significant results were: latency by 1 (2.1 c/deg) and 0.5 mm (4.9 c/deg) FDP stimulation to the center was shorter than that to the periphery; latency by 4 mm (0.8 c/deg) FDP stimulation to the periphery was shorter than that to the center. As for 2 (1.5 c/deg) and 6 mm (0.5 c/deg) FDP stimuli, no significant difference could be observed. Conclusions: A higher spatial frequency FDP stimulation to the center elicits PPR more strongly than that to the periphery, whereas a lower spatial frequency FDP stimulation showed the opposite result, with peripheral stimulation being more effective than central stimulation.