Which is bigger: >---<
April 30, 2016 7:55 PM   Subscribe

Optical illusions are not universal, and the differences in how we perceive them can help us to understand cognition. The famous Müller-Lyer illusion is not universal, but differs by culture, with some African tribes unable to see the illusion at all - possibly because of differences in environment. Individuals with autism seem less sensitive to the Sheppard's table illusion, which might help improve an understanding of the condition. Differences in responses are possible because different illusions trick your brain in different ways. BBC has a great history of the evolution of optical illusions, and, finally, here are some auto-kinectic illusions, because they are awesome.
posted by blahblahblah (22 comments total) 32 users marked this as a favorite
The original title was, "Which is bigger: < --- > or >---<", but one of those got interpreted as HTML and disappeared (an illusion!), leading to the odd title it has now.
posted by blahblahblah at 7:58 PM on April 30, 2016 [7 favorites]

A lot of those auto kinetic illusions don't work for me, or work in different ways (for example, the yellow lines stay still but the blue rocks shift). Wonder what that means.
posted by infinitewindow at 8:03 PM on April 30, 2016

Wait - it's the lines that are supposed to shift? The rocks shifted for me and mr. mitt.
posted by ovenmitt at 8:13 PM on April 30, 2016

Notions of perspective and foreshortening are relatively recent in the history of drawing things.

Illusions that play on perspective and foreshortening only work on people who are already acculturated to those ways of drawing things.
posted by yesster at 8:20 PM on April 30, 2016 [1 favorite]

Also, if you like auto-kinetic illusions, these are the ultimate ones by Akiyoshi. This and this are insane. Since the second one is a gif, I thought it might actually move and had to hold my hand over it to confirm it didn't.
posted by blahblahblah at 8:23 PM on April 30, 2016 [4 favorites]

by showing the illusion to an African tribe that lived in circular huts and therefore had no perceptual experiences with corners. People in this tribe didn't seem to be fooled by the illusion thus supporting the "experience with corners" explanation of the illusion.
After having been burned by a similar claim that turned out to be an egregious lie before, I'm going to have to see some cites on that.
posted by traveler_ at 8:28 PM on April 30, 2016 [4 favorites]

Yeah, that lack-of-experience-with-corners thing is laughably misguided.
posted by a box and a stick and a string and a bear at 8:36 PM on April 30, 2016

The two tables on the "Müller-Lyer illusion" page made me very angry. I measured them so I know they're the same size, but my brain's telling they simply can't be the same size, dammit!
posted by Greg_Ace at 8:39 PM on April 30, 2016 [3 favorites]

It's easier to see them as the same if you squint. I suppose that's just removing details, like the legs.
posted by Rhomboid at 8:41 PM on April 30, 2016

The original title was, "Which is bigger: <---> or >---<", but one of those got interpreted as HTML and disappeared (an illusion!), leading to the odd title it has now.

It's also broken the Metafilter RSS feed!
posted by We had a deal, Kyle at 8:49 PM on April 30, 2016

Yeah, that lack-of-experience-with-corners thing is laughably misguided.

You could well be right, but that's the explanation that R L Gregory goes with in Eye and Brain and The Intelligent Eye, as I recall.
posted by jamjam at 8:53 PM on April 30, 2016

Most of the kinetic ones did nothing for me, but I remembered seeing them before. Turns out f.lux was changing the contrast enough to disable the effect.

Still, most of them moved very little if at all. On the other hand some, like the first one on the Guardian page, the green background with the pinkish beans, go crazy like they're animated. I don't have to look at them a minute, they are moving the second I look at them, straight on or out of the corner of my eye.

The ones that don't move hurt my head though, instant headache. The ones that do move don't.
I'm sure there's something to all this.
posted by bongo_x at 9:11 PM on April 30, 2016

There was a study at Yale and I saw the film, a long time ago, in an art class. Social scientists made a room and had a long wall on one side, and a shorter wall on the other side as you looked at it dead on. The back wall came in at roughly a 45 degree angle. They painted the baseboards so the perspective looked right to the western eye. When gazing with one eye covered at the very front middle of the room, it looked like a normal square room to people who are used to making up straight lines to cope with western architecture. We can't see straight lines with our round eyes, we make that all up. (I will cover why viewing nature is so relaxing to the mind later. Aside from the fact we don't have to make up a square grid in our heads the whole time, and it is less work, therefore more easy to look on.) So anyway, in the experiment a teddy bear was placed at the longer back corner of the room and the western watchers, saw the teddy bear grow when taken to the other corner of the room, and then shrink again when it was taken to the other corner. The bushmen who had been brought in for the experiment, saw no difference in size in the teddy bear. The same bushmen were taken out in vehicles, where they had never been at that time, and the speed of approach made animals seem to grow magically for them, at the time.

I taught perspective drawing to students who lived in round houses, and it was difficult to teach them about the illusion of perspective, if they had no illusions about it to begin with.

Take it from me, when you are in the city canyon and all those buildings line up perfectly and recede in proper fashion to suit your western trained vision, you are seeing an illusion created by your brain, because your eyes cannot send a signal like that from the retina, what you see is all interpretation of data, straightened up by your brain.
posted by Oyéah at 9:26 PM on April 30, 2016 [6 favorites]

It's easier to see them as the same if you squint.
posted by Rhomboid


(also, for whatever reason, squinting didn't help)
posted by Greg_Ace at 9:41 PM on April 30, 2016

Loved these, especially the history of illusions. Fascinating stuff. Also, now I reeeeally want a poster with the blue stones.
posted by lemonade at 9:58 PM on April 30, 2016 [1 favorite]

So in a high school physics class, we had a class where the teacher show us the Müller-Lyer illusion. Some particularly skeptical students insisted that the outward facing arrows image was actually shorter and demanded we break out rulers. Lo and behold, it was in fact ever so slightly shorter.

Imbued with the same sense of skepticism, I would like to note that the image at the top of that Müller-Lyer illusion page in fact does have the apparently shorter set of arrows 2 pixels shorter than the apparently longer one.

That's not to say that the illusion doesn't exist, but people need to be less sloppy in showing it!
posted by Zalzidrax at 10:47 PM on April 30, 2016 [6 favorites]

I have been bitter about the Müller-Lyer ever since the first time I was "fooled" by it, because sure as shit those lines in the middle are the same length, but when you ask me "which is bigger" I tend to assume you mean the whole thing and not just the one bit in the middle.
posted by ckape at 11:48 PM on April 30, 2016 [1 favorite]

The experience-with-corners explanation that Gregory gave isn't considered very good. The problem is that Gregory focused entirely on the classic Muller-Lyer arrows, which admittedly look a bit like corners, but you can come up with other versions of the same illusion that don't look anything like corners (e.g. the illusion still works if you put circles at the ends of the lines instead of arrowheads).
posted by painquale at 2:14 AM on May 1, 2016 [3 favorites]

The circle version of the arrows doesn't work at all for me. I'd never seen the table before, though, and just watching the one table rotate I could see the size changing on me.
posted by jeather at 5:54 AM on May 1, 2016

Oyéah, I am very personally aware of the "straight, orthogonal lines" illusion, even coming from a western upbringing, because I started wearing glasses with a fairly strong diopter a few years ago. Even after getting fairly used to them, I still find it very difficult to judge whether a line is actually perfectly straight or not without taking off my glasses.

(That many older houses that I've lived in have not had entirely level/straight ceilings or floors only exacerbates matters)
posted by Nutri-Matic Drinks Synthesizer at 1:31 PM on May 1, 2016

Thankfully I'm not in construction or I would get pretty damn frustrated with this problem.
posted by Nutri-Matic Drinks Synthesizer at 1:35 PM on May 1, 2016

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