I'm a user experience designer concerned about a new trend of blurring screens when showing a lightbox/dialog box over top (see below).
From what I know, blurry images cause the brain to work hard unnecessarily as the eye tries to focus an image. If my team really wants to blur images, perhaps I can give them guidance on how blurry the image needs to be.
Other than the dialog box in the foreground, you can see that the rest of the words are blurry but are just clear enough to make out, which makes me fear the eye is trying to focus them.
Whereas something like Apple's iPhone blurs the app icons in the background of its Search feature so much that it looks like a pretty image when you search, and it seems the eye wouldn't focus on that background:
So my questions are,
Does trying to focus a blurry image cause eye strain, cognitive load or any sort of discomfort?
At what point does the eye stop trying to focus and just accept the blur as an abstract image, something that can't be focused, at which time it might relax? Or is that point subjective and, hence, cannot be measured or put into words?