In normal brain function millions of tiny electrical charges pass from nerve cells in the brain to all parts of the body. During a seizure, nerve cells in the brain fire electrical impulses at a rate of up to four times higher than normal. Seizures cause different physical effects depending on which parts of the brain are involved and how far the signals fan out. Some people have violent seizures that knock them to the floor unconscious and twitching. Others experience less severe seizures that may only blank them out for a few seconds or more.
Some mild seizures pass so quickly that it seems the person is just daydreaming.
Often, people sense that something is about to happen to them right before a seizure. The likelihood of a seizure, as well as its type, in photosensitive individuals depends on the intensity, the contrast of the visual stimulus, and the specific frequency of flashing. Extensive EEG studies have shown that a flicker stimuli between 10 and 30 flashes per second induces the generalized epileptiform discharges and the clinical features characteristic of an epileptic seizure particularly well. Television, computer, and video game screens produce a 50 Hz flicker and a vibrating pattern at half the alternating-current frequency, or 25 flashes per second within the 10 to 30 flashes per second range. The vibrating pattern is only visible when sitting close to the television.