After my last post a reader informed me that an animated graphic included in my blog may have the potential to cause seizures. This is bad. Very bad. I don’t like people to have seizures as a consequence of reading my blogs. I’m just old-fashioned that way.
The offending blog contained a poorly constructed animation of mice dancing around a pumpkin, and I considered it a rather sad thing that such a playful, whimsical bit of fluff might cause a medical problem.
But it did make me think: just how common are seizures caused by visual phenomena? I mean, are my dancing mice a real health risk or, in the words of a friend, are they just “an annoying Internet gimmick desperately waving its hands for attention”?
It was time for some detective work.
I scoured the web and came up with the following:
Photosensitive Epilepsy (PSE)
About 3 million individuals across the United States are affected by epilepsy and seizures.1 “Symptomatic seizures” are caused by identifiable diseases or brain abnormalities. Known causes for seizures include genetic defects, tumors, infections, head trauma, stroke, Alzheimer’s disease, and a number of other medical concerns. Medical professionals label a seizure as “cryptogenic” if its cause cannot be found.
In a special type of epilepsy called “Photosensitive Epilepsy” (PSE) individuals exposed to visual stimuli, such as a flashing light or changing color patterns, can lapse into a seizure. With the prevalence of TVs, computer monitors, and other electronic screens that dominate modern society, individuals with PSE must be especially careful to avoid seizure-inducing stimuli.
How Common is Photosensitive Epilepsy (PSE)?
About 1 in 4,000 individuals ages 5-24 are affected by PSE. Clinical PSE is found in about 2% of individuals of all ages who have seizures.2
What Causes PSE?
Researchers are divided on the specific cause of PSE, but it is characterized by abnormal sensitivity of the brain to visual stimulation.3
Who is affected?
PSE appears to be transmitted genetically, so if a parent is affected by the disorder, their children are more likely to have it as well.4 It has an early onset between 2 to 18 years, with a peak between 12 to 13 years.5Two-thirds of those affected are females; however many studies reported a higher incidence of photosensitive seizures in young males.
One study explained this discrepancy between diagnosis and disease by citing the larger proportion of young males playing video games with PSE inducing stimuli.6 However, this study, like many others of its kind, was done in the ‘90’s and early 2000’s. In the intervening decade female use of video games has skyrocketed7 (as fellow MTSG blogger Shara Evans can attest), so it would be interesting to see if this epilepsy pattern has evened out in a future study.
Visual Factors that Make Seizures More Likely for Those with Photosensitive Epilepsy
Studies have found that brighter stimuli are more likely to induce seizures. Sudden changes in the luminance of a screen also contribute to seizure potential. Because of this, television broadcast guidelines include specifications for changes in screen luminance during programming.
Some seizures can be triggered by viewing patterns. Black white stripes are the most common offender, and when combined in a vibrating or flickering pattern, the incidence of seizures increases. Although stripes occur often in everyday life, viewing them on a video screen appears to increase their potential to cause seizures.
The flash, or flicker frequency, is the most important factor in determining photosensitivity to video screens. Flash frequencies with the highest likelihood of causing a seizure occur at both 9-18 flashes per second and 50 flashes per second.
In the early ‘90’s researchers in Great Britain began investigating seizures that had taken place among children playing the video game “Super Mario World.” 9They found that the bright backgrounds and flashing patterns that the game contained lent themselves to seizures among children susceptible to PSE. In addition, children playing on a 50 Hertz television experienced a greater likelihood of a seizure (the scientific measurement of “Hertz” refers to frequency per second).
This susceptibility to flash frequency also extends beyond video monitors to phenomena present in everyday life. For instance, one case study reported that a man being transported by a helicopter after a medical emergency experienced a seizure in response to the flashing light and dark pattern created by the helicopter blades and sunlight.10
The length that an individual is exposed to stimuli also influences their risk of having a seizure. In other words, a child with PSE is much more likely to have a seizure after five minutes of watching flashing lights versus one.
Flickering red or red and blue colors have been found to cause seizures in many PSE individuals. One of the most famous examples of this seizure-inducing phenomena occurred during the Japanese airing of a Pokémon cartoon on December 17, 1997.11 In the cartoon, an explosion hits a character, followed by several seconds of flashing red and blue. To make matters worse for those susceptible to PSE, the flashes occurred at 12 flashes a second.
After this cartoon aired, 682 people experienced seizures and were taken to hospitals. It was not a good day to “Catch ‘Em All.”
On a side note, the flashing red and blue police lights on a police car have not been shown to be seizure-inducing.12 So while there are plenty of reasons to be worried when you see the red and blues flashing in your rear-view mirror, having a seizure is not one of them.
Research has found that increasing cognitive demands on PSE-sensitive individuals exposed to one of the stimulus described above increases their risk for a seizure. For instance, individuals playing puzzle games projected on a 50 Hertz screen displayed a high likelihood of having a seizure. In addition, the “Super Mario World” study cited above found that individuals actively playing the game were much more likely to have a seizure than those passively watching the video game being played by someone else.13
Do My Dancing Mice Pass the Epilepsy Test?
At the start of this article I discussed the annoying/fancifully charming dancing mice graphic that I used in my last blog. So, after all my research, are they really dangerous to individuals susceptible to PSE?
Well, let’s check it out.
CLICK HERE to view the animated mice graphic (just in case it somehow does induce epilepsy, I’m not putting it in this blog!).
First, the overall brightness of the graphic never changes, and there are no stripes or flashing shapes occurring for any duration. The frolicking mice themselves move at a frequency of one frame per second (far below the offensive 9 flashes per second threshold), and there is no red or blue present. Aside from my sorry attempt at transcendent animation, I have to admit it’s really minimally cognitively engaging (unless you are really, really into dancing mice). I suppose that duration could be an issue if you stared the graphic for several minutes, but I think most people scan down the page (or immediately click off my blog!).
Now, I’m not a physician, but according to the guidelines presented in the research, it would appear that the dancing mice are kind of…well…OK in a non-seizure-inducing sort of way.
As for charges that it’s gimmicky, shticky, and ultimately sort of annoying, I really can’t defend it.
PS If you are concerned that your website might be seizure inducing, check out this free, downloadable “Photosensitive Epilepsy Tool” (PEAT): http://trace.wisc.edu/peat/. Developed by the University of Wisconsin’s Trace Center, it analyzes websites using many of the criterion listed above to help developers identify potentially problematic animations and stimuli.
1The Epilepsy Foundation. (n.d.). Incidence and Prevalence. Retrieved from http://www.epilepsyfoundation.org/aboutepilepsy/whatisepilepsy/statistics.cfm
2Epilepsy Therapy Project. (n.d.). Photosensitive Epilipsy. Retrieved from http://professionals.epilepsy.com/page/photosensitive_epilepsy.html
3Tauer, U., Lorenz, S., Lenzen, K. P., Heils, A., Muhle, H., Gresch, M., Neubauer, B. a, et al. (2005). Genetic dissection of photosensitivity and its relation to idiopathic generalized epilepsy. Annals of neurology, 57(6), 866–73. doi:10.1002/ana.20500
5Epilepsy Therapy Project. (n.d.). Photosensitive Epilipsy. Retrieved from http://professionals.epilepsy.com/page/photosensitive_epilepsy.html
6Trenite, D.G.A, da Silva, A.M., et al. (2002). Video games are exciting: A European study of video game-induced seizures and epilepsy. Epileptic Disorders. 4(2). 121-8. Retrieved from http://www.jle.com/en/print/e-docs/00/01/AD/B3/article.phtml
7Williams, D., Consalvo, M., Caplan, S. & Yee, N. (2009). Looking for gender: gender roles and behaviors among online gamers. Retrieved from http://dmitriwilliams.com/lfgpaperfinal.pdf
8Zifkin, B. G., & Inoue, Y. (2004). Visual reflex seizures induced by complex stimuli. Epilepsia, 45 Suppl 1, 27–9. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/14706042
9Trenite, D.G.A, da Silva, A.M., et al. (2002). Video games are exciting: a European study of video game-induced seizures and epilepsy. Epileptic Disorders. 4(2). 121-8. Retrieved from http://www.jle.com/en/print/e-docs/00/01/AD/B3/article.phtml
10Cushman, J. T., & Floccare, D. J. (n.d.). Flicker illness: an underrecognized but preventable complication of helicopter transport. Prehospital emergency care : official journal of the National Association of EMS Physicians and the National Association of State EMS Directors, 11(1), 85–8. doi:10.1080/10903120601021457
11Wikipedia. (n.d.). Dennō Senshi Porygon. Retrieved from http://en.wikipedia.org/wiki/Denn%C5%8D_Senshi_Porygon
12Vainstein, G., Yoffe, V., & Gadoth, N. (2000). Can police car colored flash light induce encephalographic discharges and seizures? Croatian medical journal, 41(3), 319–22. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/10962053
13Trenite, D.G.A, da Silva, A.M., et al. (2002). Video games are exciting: A European study of video game-induced seizures and epilepsy. Epileptic Disorders. 4(2). 121-8. Retrieved from http://www.jle.com/en/print/e-docs/00/01/AD/B3/article.phtml
[Update 11/05/2012: As per Elizabeth's comment below, I have added a caption on the police light photo to make it more apparent that there is no evidence that they cause seizures.]