The Ishihara color plate test is something we've all seen. You look at a round patch of dots, made up of a mix of, maybe, orange and yellow dots, with a number "5" (or whatever) right in the middle. The 5, however, is comprised of green dots.
It's the usual test for color blindness. I have also recently discovered, in researching PCA, or the visual variant of AD (which is the form most affecting my husband,) that this test is also useful for detecting simultanagnosia, or an inability to distinguish individual parts within complex images. In other words, you can't see two things at once, sort of.
I try to tread lightly in my "at-home" testing, because there's really no point in it other than my own curiosity, and we don't like to rub J's deficits in his face unnecessarily. But I saw no harm in a quick color plate test, so first I asked him to identify numbers I had simply typed on a word-processing page. No problem. Then I showed him the same numbers in the form of Ishihara blocks. Could not see the numbers. Then I asked him what colors were in the plates, to verify that the problem was NOT color-blindness. Indeed, he could absolutely identify the colors involved, but could not distinguish the numbers. Positive test for simultanagnosia, a hallmark of PCA. As if I didn't already know.
I don't know why I do things like this. I guess I just like to classify.
Ishihara color plate tests can be found online. Just google.
OH MY goodness! I just did this with my husband and he had the same results as Emily's husband! I had the same thoughts, too...........why am I trying to prove something I already know? But, it does, in some way, satisfy my curiousity!