The effect of television frame rate on EEG abnormalities in photosensitive and pattern-sensitive epilepsy

Seizures provoked by television viewing may be triggered by patterns in the television image or by flicker from the display itself. We examined the incidence of EEG abnormalities elicited by patterns displayed on television sets with two different frame rates to evaluate the likely contribution of photosensitive and pattern-sensitive mechanisms to television- and video-game epilepsy.

Televisions with frame rates of 50 and 100 Hz were used to present 35 patients who were photosensitive or pattern-sensitive with grating patterns. These patterns comprised vertical square-wave and sine-wave gratings of 90% contrast, and the spatial frequency was varied between 0.25-7 cycles/degree. EEGs were analysed for laboratory sensitivity to patterned and unpatterned intermittent photic stimulation (IPS).

Significantly fewer EEG abnormalities were elicited by patterns displayed on the 100 Hz frame-rate television than on the 50-Hz frame-rate television. No abnormalities were observed in response to the blank screens of either television. Thirty-three patients showed abnormalities in response to patterned IPS but only 15 in response to diffuse flash. Two patients showed no laboratory evidence of photosensitivity. Patients who were sensitive to patterned IPS at 50 Hz were significantly more likely to demonstrate abnormalities to patterns displayed on the 100-Hz frame-rate television than were patients who were not sensitive to 50-Hz patterned IPS.

We suggest that for many patients, the combination of high-contrast patterns and screen flicker may elicit the observed EEG abnormalities. For patients with sensitivity to screen flicker, the use of a high frame-rate television may be beneficial in reducing the risk of seizures.