I can't see optical illusions
February 4, 2007 9:04 AM   Subscribe

Why can't I see optical illusions like this?

My husband looks at this and can see a spinning motion. I generally have trouble seeing these sorts of optical illusions. I can see the "negative space" illusions, like the one with the vase and the faces, and the necker cube works for me as well.

Most of my life I couldn't see 3-D images either, presumably because I had very bad eyesight in my right eye. I had Lasik a few years ago, and now I can see 3-D images, but I've had no further luck with the optical illusions.
posted by Evangeline to Health & Fitness (26 answers total) 2 users marked this as a favorite
This isn't a 3D illusion, it has to do with tricking the motion detection system in your peripheral vision.
When I look at a center ring, I see the external rings seem to slowly rotate.

Do you have any other problems with peripheral vision?
posted by demiurge at 9:12 AM on February 4, 2007

Response by poster: Demiurge - I don't think I have any problems with my peripheral vision, but is there a way to test it? By the way, I know "the snakes" are not a 3-D illusion. I just brought up my past problems seeing 3-D images in case there might be some connection.
posted by Evangeline at 9:19 AM on February 4, 2007

I can amplify the effect by moving my eyes. Perhaps that will help?
posted by clord at 9:19 AM on February 4, 2007

I can force myself to stop viewing the illusion, as clord suggests. If I blank out and stop trying to focus (the act of which is hard in such an illusion and apparently makes my eyes move), the illusion "stops". Perhaps you are trying too hard to view the illusion.
posted by geoff. at 9:30 AM on February 4, 2007

I could never see the 3D illusions, and never have figured it out. On the other hand, I have no problem seeing this.

As demiurge said, the image relies on being large enough so that some of it must reside in your peripheral vision. Are you viewing this from far away? Have you tried reading the text on the page, and forcing the image into your periphery?

The illusion also depends on seeing four differences in luminance. The colors are a red (as well as green, blue, yellow, etc.) herring. I desaturated a portion of the image and it still worked.

I uploaded it to my underused flickr account. Can you see four shades of gray? Does it work then?
posted by kingfisher, his musclebound cat at 9:30 AM on February 4, 2007

I think it's pretty clear that your trouble with 3-D/stereoscopic images was due to poor acuity in one eye, especially if you can see them now.

But I'm not sure it's related to your trouble with the motion illusions. Most of those - including the snakes illusion linked to - are perceptible even with one eye closed.

Stereoscopic images and these motion illusions require you to be doing different things, usually. To see 3-D illusions you have to sort of unfocus your eyes a little bit, so that you're receiving the conflicting visual cues at the same time. For the snakes illusion, don't do that - don't try to take the whole image in at once. Focus on a point, then flick your eyes to another focus point; as you do that the "motion" should be apparent in the periphery.
posted by miagaille at 9:32 AM on February 4, 2007

Do you have any problems with the other motion illusions on that site?

this and this are stronger for me than the "snake" one.
posted by demiurge at 9:32 AM on February 4, 2007

MR. PITT: You said keep your eyes out of focus, which is misleading. You want DEEP focus!
posted by wfc123 at 9:39 AM on February 4, 2007

To emphasize what miagaille said above - All these illusions, including the ones demiurge links to, happen even with one eye closed. They dont depend on depth of vision. That takes the whole bad vision/Lasik thing out of the picture since you should have always been able to see these illusions with your "good" eye.
posted by vacapinta at 9:41 AM on February 4, 2007

Response by poster: Yay! The two other images demiurge posted work for me. The effect is much more pronounced for my husband, but I can definitely see movement.

Kingfisher - I'm just getting to a Flickr log-in page when I click on your link.
posted by Evangeline at 9:42 AM on February 4, 2007

Sorry, maybe this link? Make sure you try the largest size.
posted by kingfisher, his musclebound cat at 9:44 AM on February 4, 2007

Most of my life I couldn't see 3-D images either, presumably because I had very bad eyesight in my right eye.

From birth, right? You've probably got a mild case of amblyopia ex anopsia.
posted by ikkyu2 at 10:03 AM on February 4, 2007

Response by poster: I don't remember the first time I realized I couldn't see 3-D images. In fact, I didn't know I had any trouble with my eyesight until 6th grade, when I started writing down the wrong answers for math problems that my teacher would write on the chalkboard. Even then, I didn't know what the problem was - it was my teacher who told me parents.

Ikkyu2 - is amblyopia ex anopsia the medical term for "lazy eye"? I've suspected before that my right eye was a little lazy, though everyone I've talked to says they can't see it. It seems to me that every once in a while when I look in the mirror I catch it wandering, but that may be an illusion. I'm also sometimes bothered when I'm writing or reading by constantly being aware of seeing the right side of my nose.

Thanks, Kingfisher, I got that link, but I still can't see the movement.
posted by Evangeline at 10:45 AM on February 4, 2007

The parent page of those posted above has several other really good ones. Ignore all the Japanese text and just scroll. I particularly like the square one with red, orange, and yellow boxes in it, the third one from the top. Not only does the inner box look twisted (without being) but it also seems to jiggle relative to the outer frame.
posted by Steven C. Den Beste at 10:52 AM on February 4, 2007

I'm legally blind in my left eye. I still see it, presumably because I have peripheral vision in it. Try looking at one of the rings and gently pay some attention to rings other than the one you are looking at.
posted by Ironmouth at 11:17 AM on February 4, 2007

You probably have a small lazy eye. I have one too. My left eye is also smaller. As for 3-D vision, you really can't know if you have it or not, I guess--I've never been able to understand if I have any or not based on my eye issues.
posted by Ironmouth at 11:19 AM on February 4, 2007

I wonder if the Snakes effect is dimished by astigmatism. I have that, and if I take my glasses off the rotation virtually stops.
posted by beagle at 11:43 AM on February 4, 2007

Couldn't it just be about having a brain that processes information in different ways? I mean, the truth is that the images are not moving. Maybe some people are just wired to take in all the information that's there, without needing to deal with some of it by imagining that the image is moving.
posted by bingo at 12:21 PM on February 4, 2007

No, Evangeline, ambylopia ex anopsia has nothing to do with lazy eye. It refers to the fact that the visual cortex of the brain (in the occipital lobes) can't develop properly if one or both eyes can't see.

The critical period, sometimes termed the plastic period, for this is ages 1-6 years; if the eye is correctable but uncorrected during this time, later correction doesn't fix the problem.
posted by ikkyu2 at 12:38 PM on February 4, 2007 [1 favorite]

Seconding the proposition of "amblyopia ex anopsia" or something similar.

My brother was born with fully-formed, but badly-aligned, eyes. Much surgery, and years of theraputic eye patches and corrective glasses later, his vision has been corrected well enough to drive.

But, because his eyesight was so poorly formed for so many years, he still lacks many low-level eyesight functions that we take for granted: he has trouble differentiating foreground from background, for instance. He generally has to focus directly on a thing, and necessarily pays little attention to his peripheral vision. However, unless you closely observed him or spent time with him, it's unlikely that you'd ever really know. He's just another kid with glasses.

It's entirely possible that your brain has simply wired itself differently. Certainly, you can see normally, but you do not process the information in the standard way.
posted by Netzapper at 3:18 PM on February 4, 2007

Just speculating here, but I heard something a few years ago about right-brain/left-brain connectivity. Apparently if a child starts walking without having crawled around for a while first, they don't develop some of the RB/LB connections properly, and they have problems with things like comic books, for example, visual situations in which LB-type language is associated with RB-type images.

Could this account for the "brain-wiring" speculations by others above? Can you ask your parents about how you started walking?
posted by Araucaria at 3:23 PM on February 4, 2007

i don't see any motion when looking at this, whereas my wife totally does. must be something specific to each person (although presumably the majority of people can see it).
posted by jjsonp at 4:12 PM on February 4, 2007

Response by poster: Araucaria, that's very interesting. I never learned how to crawl when I was a baby. I just scooted around on my butt until I finally walked, which was very late, though I can't remember how late.
posted by Evangeline at 4:30 PM on February 4, 2007

As already said, the illusory motion appears only during eye movement. I just figured out a more specific clue: at least for me, it only works with saccadic (rapid, point-to-point) movement.

Those for whom this illusion works, try moving a finger across the screen and following it with your eyes. That causes steady eye movement that, at least for me, fails to "rotate" the "snakes".
posted by Anything at 10:12 PM on February 4, 2007

This followup to my previous comment is complete speculation. I'm an undergrad who's taken exactly one course of perceptual psychology.

If I haven't read my homework wrong, people normally have a specific process in the visual system that facilitates the constancy of perception before and after a saccade, so it won't look like objects are actually zapping from place to place every time one move one's eyes. I believe it's called "saccadic remapping".

My uninformed hypothesis is that the perceived rotation is caused by inaccuracy in this remapping, inaccuracy that is so slight that other processes basically "assume" the remapping to be accurate, which in rare cases results in an illusion of motion

Now, if I'm right, we have at least three or four possible answers to your question.
  • You have super-accurate saccadic remapping. Congratulations, and use your powers for good!
  • Your saccadic remapping is abnormally inaccurate or otherwise weird, and has an undeveloped connection to the motion detection processes. Do you have keeping an eye on, say, butterflies or little birds as they fly to and fro?
  • Your remapping is really weird or undeveloped. Do objects, in fact, seem to zap from place to place every time you move your eyes? Now, you might not actually experience it this way, since your mind might have learned to ignore this effect, or work around it somehow.
  • Your eyes don't do saccades in the first place. Have your husband look at your eye movements as you look at different parts of his face, and ask him to do the same for someone else, and compare. Perhaps he can see if your eyes move less rapidly. But I don't know if this would actually be reliably detectable by a human observer.
I must still emphasize that everything I've said may be completely implausible.
posted by Anything at 11:53 PM on February 4, 2007

Damn, I meant to say Do you have trouble keeping an eye...
posted by Anything at 11:58 PM on February 4, 2007

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