Just to be clear, I am not an expert, I am just passing on what advice is given by experts.

I think this isn't about refresh rates in general but about high contrast differences in imagery that changes at these rates? So a non-flashing video isn't the problem, but video of a flickering strobe light displayed on any tech would be a problem?

As a layperson, I read their advice as meaning the 60hz is highest there has been a danger, but main danger is 10-25hz?

Yes, and they're covered in the guide, but there's a risk that someone views the animation without any restrictions in place (on someone else's device, on a shared link etc).

Would the options in Animations and accessibility be useful here?

One time a house guest went catatonic. The only possible thing I could think of as an external physical trigger was a small flashing light on an electronic keyboard. I immediately thought back to the film Andromeda Strain.

Misdiagnosis however.

But I wonder about frame rates, as I can be very prone to motion sickness with certain films and video games.

Again, probably not related.

Haven’t seen to much web flashing since HTML 3.0 <blink> 26 + yrs ago.

Yeah, that's got to be wrong... If it triggered seizures, _any_ shared office space would be a major safety hazard.

Although, on a 60hz CRT, pixel intensity fades between each refresh, causing a constant "flickering wave" across the screen. (Not entire screen at once though.)

While on 60hz LCD (and similar), the pixels keep the same intensity while waiting for the next update. So no fading in between.

So that reference to 60hz may be from older tech, maybe?

Yeah, I saw on Wikipedia just now that even static images can trigger seizures in some people. I knew that rapid changes in luminance over *time* can cause seizures, but I didn't know rapid changes over *space* can do it too!

And yeah, the glitch aesthetic is pretty much exactly that. High contrast, lots of visual noise, resembling the output of buggy graphics code. Parsing such an image is pretty hard on the brain, even if it doesn't seize.

@FediTips @buffyleigh

Wikipedia describes it as rapid changes in luminance. Equally rapid and dramatic changes in color, without a change in luminance, do not trigger seizures. https://en.wikipedia.org/wiki/Photosensitive_epilepsy

I'm reminded of a GIF I once saw, from some people who were apparently *trying* to trigger photosensitive epilepsy in unsuspecting website viewers. For their own amusement, apparently. Jerks.

It was called “Epilepsi” (sic). Very rapid, very intense flashing. On that day, I found out that I'm not epileptic…the hard way!

Note that 60Hz is also the refresh rate of most screens, so they aren't *capable* of displaying a flash that's too fast to trigger seizures.

Rise time is a factor too.

Thus Xenon strobes, camera flashes, and LEDs with the usual fast switching, are more troublesome than incandescent sources.

Car tail lights strobing with sharp risetimes at epileptic trigger frequencies are common.

Single flashes can precipitate seizures.

When it happens a lot, well at least that's how I felt, you kinda get used to it. It remains exhausting, physically too even if there are no injuries. But when I haven't had one in a week, it feels worse somehow. Don't know if it's just me, though. Thank you for caring

That's a fair point

I have autoplay off for everything, but when I open in another tab and it isn't on my instance, it's sometimes animated. Which sometimes caused seizures.

I am not an expert, but for example this epilepsy website describes it as:

"...caused by being exposed to flashing or flickering lights or high contrasting patterns."

"Some people are sensitive to geometric patterns with contrasts of light and dark such as stripes or bars."

https://epilepsysociety.org.uk/about-epilepsy/epileptic-seizures/seizure-triggers/photosensitive-epilepsy

As far as I can tell this means it happens with specific kinds of animation/movement rather than all animation.

According to https://www.epilepsy.org.uk/info/seizure-triggers/photosensitive-epilepsy the frequencies are as follows:

10 to 25 Hz
Flash rate range that is most likely to cause a seizure in people with photosensitive epilepsy

3 Hz
Slowest flash rate that could trigger a seizure for some people

60 Hz
Fastest flash rate that could trigger a seizure for some people

(Hz or Hertz is how many times a second the light is flashing)