WCAG Example suggests "blurring" does not affect animation triggering vestibular motion perception (but it can)

[cookiecrook]

The definition of motion animation excludes "blurring", which appears incorrect to me.
https://www.w3.org/TR/WCAG22/#dfn-motion-animation

motion animation
addition of steps between conditions to create the illusion of movement or to give a sense of a smooth transition

EXAMPLE
For example, an element which moves into place or changes size while appearing is considered to be animated. An element which appears instantly without transitioning is not using animation. Motion animation does not include changes of color, blurring, or opacity which do not change the perceived size, shape, or position of the element.

Blurring is commonly used to elicit a "depth of field" effect (simulating an artifact of the eye's iris or camera aperture)... The resulting illusion is one of animation depth changes (in the z index), which is known to be a common trigger for vestibular motion disorders.

I would suggest the word "blurring" be removed from this example text, or perhaps changed to "dissolving"??? Though keeping both dissolving and opacity may be redundant, so my preference is just to remove the word "blurring."

You might also add "or perceived distance/depth" to the last sentence too.

…which do not change the perceived size, shape, position, or distance/depth of the element to the viewer.

[mraccess77]

Personally, blurred images give me an instant headache and I can't look at them. This included blurred background filters on people's video feeds. So, I'd be in favor of including blur as a problematic aspect.

[mbgower]

@cookiecrook I think a few things are combining to make this less helpful than it could be.

First, the qualifying phrase "which do not change the perceived..." is intended to make it clear that none of those things is excluded. Instead, animation is not considered to exist if there is no motion perception from the application of any change (be it color, blurring or opacity).

We've added in em dashes to make that apposition more emphatic. Some felt that with this in place it was fine to leave blurring in there; however, given your concerns, it was felt more prudent to just remove it, since it is just an example. The PR now reads:

For example, an element which moves into place or changes size while appearing is considered to be animated. An element which appears or changes instantly, without transition/animation steps, is not using animation.

Motion animation does not include changes – such as changes of color or opacity – that do not alter the perceived size, shape, position, or distance/depth of the element.

[cookiecrook]

@mraccess77 wrote:

I'd be in favor of including blur as a problematic aspect.

Yes, that what this issue is proposing... The shipping prose currently has "blur" listed as a non-problematic effect, which does not support your need.

The related PR corrects that mistake, so that blur-based motion (such as a simulated depth of field change) is now implicitly included as problematic, rather than being explicitly excluded.