Anime-induced epilepsy

Nowadays, it is fairly common to see a warning that appears before the opening sequence of an anime. For example, consider the following warning that precedes Minami-ke:

(Minami-ke is one of my favorite series of the fall season. The character-based comedy is very well done, and it doesn't seem like it's going to take a nosedive like Zetsubou Sensei.)

Ok, so what is the origin of such a warning. Well, when reading a book, it is advised to have a decent amount of light so as to not strain the eyes. However, because a television emits its own light, there is usually plenty of light to see what's going on in the TV. As far as distance is concerned, I don't think there is any real reason for keeping the attended region small on the retina, so much as ensuring that strain is not occurring due to focusing on a nearby object for an extended period of time. (Books are generally another story, because there is constant movement of the eyes, I think.)

I checked out some of my anime DVD's and wasn't able to find a warning, so presumably, it only happens for the Japanese television broadcast. One way to check my hypothesis would be to examine anime broadcasts recorded prior to 1997 and broadcasts made after 1997 to see if the presence of the warning jumps from zero to a high percentage.

To understand the origins of this warning, I think we need a trip back to 1997, when the now infamous "Dennō Senshi Porygon" (でんのうせんしポリゴン) episode of Pokémon was aired in Japan. At some point in the episode, an explosion occurs that results in flashing of bright red and blue lights at 12Hz for 6 sec total. (4 sec for most of the screen, and 2 sec for all of the screen) Of course, these are prime conditions for inducing photosensitive epilepsy: high contrast, red color (certain wavelengths work "better" than others), a frequency between 5 and 30 Hz, and flashing across a large portion of the visual field. The episode is now banned worldwide, and hundreds of Japanese children were treated for symptoms, although mass hysteria resulted in some 12,000 individuals reporting symptoms. You can find more details on wikipedia's articles for photosensitive epilepsy and Dennō Senshi Porygon. The large number of epileptic victims was probably due to the extreme popularity of Pokémon, a show whose primary audience falls right into the population that is most susceptible to photosensitive epilepsy. The "best" part of the story is that, in a stroke of pure stupidity, Japanese news programs that reported on the story later that day, replayed the scenes in question, sending a second round of epileptic victims to hospitals.

Ok, so what then, does the warning accomplish. By increasing distance to the television, the amount of visual field occupied by the television is decreased. Also, increasing ambient light decreases the resulting contrast of scenes presented. While these changes serve to alleviate the inducing of photosensitive epilepsy, it probably is not terribly important, as I'm sure television producers are now aware of the conditions to avoid so that viewers don't develop symptoms.