My evil twin, psychologist and skeptic Richard Wiseman, has another winner: a video playing with your blind spot.
Very cool! I love illusions, and so I used to do all the blind spot tests when I was a kid… but I never knew this about it. I have lots of ideas about how this might work, but I’ll have to do a spot (haha) of research on it.
If you went to BadAstronomy.com and found yourself here, never fear: the BA Blog has moved to its new home at Discover Blogs. The original BA site (with the Moon Hoax debunking and all that) is still online, too.
Phil Plait, the creator of Bad Astronomy, is an astronomer, lecturer, and author. After ten years working on Hubble Space Telescope and six more working on astronomy education, he struck out on his own as a writer. He has written two books, dozens of magazine articles, and 12 bazillion blog articles. He is a skeptic, and fights misuses of science as well as praising the wonder of real science.
Contact me: The Bad Astronomer "at" gmail "dot" com
|
| Bad Astronomy is a Wikio Top Blog! Clearly, Wikio has excellent taste. | |
 | ||
 | Bad Astronomy was chosen as one of Time.com's Best Blogs of 2009. |
 |
"Reading this book is like getting punched in the face by Carl Sagan. Frightening, but oddly exhilarating."
-- Daniel H. Wilson, author of How to Survive a Robot Uprising
DISCOVERmagazine.com: Latest Articles on Space DISCOVER Blogs: The Loom
June 29th, 2009 at 12:25 pm
Amazing! I wonder why you can still see the whole black bar though.
June 29th, 2009 at 12:33 pm
My understanding is that the brain is hard-wired to try to “fill in the gaps” when possible. A head is too complicated to deal with, but assuming a continued black bar is somewhat easier.
An interesting test would be to have a bar that was black on both sides but, say, white in a narrow band in the middle. Then when he moved it up to the blind spot, would the brain fill the whole bar in as black?
June 29th, 2009 at 12:34 pm
The black bar is filled in for the same reason you never notice the blind spot to begin with – the retina fills in patterns, even fairly complex ones. I remember an article in Scientific American probably 15 years ago which had all sorts of fun blind spot experiments, including several with patterns which had missing sections, which would get magically filled in when put into the blind spot.
For me, watching this video in fullscreen on my 24″ monitor meant not having to move my head much at all for it to happen. It’s a good thing I usually work with both eyes open or else I’d start to worry about how many pixels I’m “wasting.”
Also, note that it can only fill in details for things which extend outside of the blind spot to begin with. His head is entirely inside the blind spot, so there’s nothing to interpolate from. (Insert snarky commentary about CSI’s magic image processing here.)
June 29th, 2009 at 1:24 pm
Heh. I noticed when he raised the black bar above his headless shoulders, some of his torso disappeared while his shoulders and arms remained. Probably just saccades, unconscious jerks of my eye.
June 29th, 2009 at 1:37 pm
How much of this one is influenced by sensitivity to peripheral motion? The head doesn’t move much relative to the hands, and you notice the movement of the black bar.
June 29th, 2009 at 1:43 pm
I think Jeremy and Fluffy got it.
June 29th, 2009 at 1:58 pm
Fluffy’s right — you’re seeing the bar outside the blind spot, and the mind fills in the gap within it. Meanwhile, the head falls completely within the blind spot and thus vanishes.
Jeremy: I’m pretty sure the white would disappear, but I’m not certain if this is dependent on the speed at which the bar moves.
PhilB: He could be shaking his head or nodding within that spot and you wouldn’t notice it, as long as your eye is locked on the X. The issue is that peripheral movement tends to attract attention, even briefly, and that temporarily shifts the position of the image on your retina until his head falls outside the blind spot.
June 29th, 2009 at 1:59 pm
Something like this was the very first thing I tried out once I found out about the blind spot.
OK, if I stare at one dot on a note card, at a certain distance the other disappears. What if I make it bigger? Odd, eventually I see the whole dot… what about a long line with a little tick on it?
Turns out the tick disappears and I see just the line, just like happens at the end of this video.
I think the reason people don’t understand how this works is because they imagine themselves looking at a screen that shows what their eyes see. In that case, it would be kinda odd to fail to notice a group of dead pixels. But as it *actually* is, I don’t think it’s that odd that you can’t really see it even if you look. I mean, consider the vast majority of your body that fails to let you see – you don’t see “black” like you closed an eye, there’s nothing there to not see with. Combine that with all the image processing that goes on in your brain and you get reality invisibly bending around the blind spot in such a way that you can’t even see any distortion.
June 29th, 2009 at 2:07 pm
I have mono-ocular vision. Doesn’t work for me.
June 29th, 2009 at 3:08 pm
at what distance do you guys get the blind spot … I’ve tried range from 3m (1oft) to having my face stuck at the monitor still can get Richard’s head to vanish
– other blind spot illusions seemed to have worked for me :’(
June 29th, 2009 at 3:09 pm
Doesn’t seem to work for me. I wonder why?
June 29th, 2009 at 3:27 pm
Nope, doesn’t work for me either. With or without glasses, no difference. Head is always there
June 29th, 2009 at 3:44 pm
You guys have to follow the instructions. You need to look through your left eye and stay focused on the cross to the right, and move your head in and out until the head disappears – and you can’t look over at the head to see if it’s gone.
If you only have a functional right eye then you’d need to horizontally mirror the video, or measure the distance between the head and the cross and put some sort of indicator on the wall opposite the head. The whole point of this is that there’s a small-but-prominent part of the retina which has no receptor cells because that’s where the optic nerve attaches (and the retina evolved in a rather slipshod manner).
The distance isn’t important so much as the angle. Unfortunately, because of the very phenomenon that is being demonstrated here, it’s very difficult to know where it is, and it might even vary between people.
For me, on a 24″ monitor with the video playing full-screen, my head is about a meter away when it happens. That appears to be about 30 degrees of separation, as a complete off-the-cuff estimate.
June 29th, 2009 at 3:46 pm
I got his head to disappear, but because he was talking, I kept shifting my focus back to Richard. Bam! There’s his head. Look back at the ×and it’s gone again.
June 29th, 2009 at 4:25 pm
Why doesn’t it work for me?
Could it that I am
I am Left handed and Right eye dominant?
Actually I am dully Ambidextrous, but prefer using my left hand for most things.
My right eye is dominant, according tot he testing I had done.
June 29th, 2009 at 5:17 pm
Blind spot?!? Must be intelligently designed! I would certainly include a blind spot if I designed an eye, wouldn’t you?
June 29th, 2009 at 5:22 pm
bigjohn756, nice touch!
June 29th, 2009 at 6:09 pm
22″ screen for me, fullscreen shows illusion appx 3 ft away.
I don’t think eye or hand dominance has anything to do with where the optic nerve attaches. I am right handed but left eye dominant, my wife is mostly ambidextrous while favoring left hand and right eye dominant and also sees the illusion.
I do wonder if there is some vertical differentiation from person to person in where the blind spot is located. When I find the blind spot, I still see his jaw moving while the upper head is completely gone. If I focus just below the X his whole head disappears.
June 29th, 2009 at 6:51 pm
For the folks who think it doesn’t work for them, keep trying. Unless you’re a squid, everyone has this blindspot. It’s just a matter of finding it, which (admittedly) can take some time…
June 29th, 2009 at 7:22 pm
My uncle’s eyes were damaged in a high-G car crash, and originally he saw black donuts in his vision. Eventually, his eyes started filling in the blind areas, but failed to notice pictures on the walls and he said reading was like pushing a washer across the page since the letters kept winking in and out. It’s been many years now, and he’s gotten so accustomed to the blind areas that reading etc. no longer takes any special conscious effort. The brain truly is amazing.
June 29th, 2009 at 7:41 pm
I couldn’t really get the effect. By the time I couldn’t see his head, I couldn’t really make out anything over there, and my face was plastered to my 15″ flatscreen. Uncorrected peripheral vision probably didn’t help the lack of focus any.
June 29th, 2009 at 7:52 pm
Nifty! I just sent this to everyone on my buddy list.
I love Richard Wiseman. If you don’t have any Wiseman books on your bookshelf, you’re really missing out.
June 29th, 2009 at 8:25 pm
Amazing. I think this is by far the best demonstration I ever saw of the blind spot.
You know, it took me a while to get it right. When he starts moving that black bar I sorta tend to go and focus on the moving thing.
June 29th, 2009 at 8:32 pm
FWIW, the book Mind Hacks covers this blind spot effect [Hack #16, p. 46-49] and many other interesting visual (and non-visual) interactions.
June 29th, 2009 at 8:33 pm
If this video had been created by anyone else, I would have expected some bloody man to jump up accompanied by a loud noise.
J. D.
June 29th, 2009 at 8:44 pm
That’s pretty cool. As others have alluded to the blind spot is the creationist’s worst night mare (sort of the way some think the banana is the evolutionist’s worst nightmare) In a remarkable instance of parallel evolution the higher mollusk such as squid and octopii have evolved eyeballs but in their case there is no blind spot. Whereas mammalian eyes evolved from brain cells which needed to turn inside out, mollusk eyes evolved from skin cells, no inversion necessary.
June 29th, 2009 at 8:45 pm
The buttons on his shirt also disappeared for me – everything in a band down the middle of his body went.
June 29th, 2009 at 9:34 pm
I wonder what would happen if you moved a vertical bar through the image side-to-side, rather than a horizontal one up and down? Would your brain fill in the gap with the bar, or continue with the background?
June 29th, 2009 at 9:40 pm
I also had a band down the middle that went away as well, I could really tell when he clasped his hands together. I love optical illusions!
June 29th, 2009 at 11:12 pm
For those who are having trouble, the blind spot is approximately 15 degrees from the focal area; that’s a ratio of about 4:1. In other words, measure the distance between the cross and Mr Wiseman’s head on your monitor and then multiply it by 4… that is how far away your eye should be for the illusion to work.
June 29th, 2009 at 11:41 pm
@Brian D
Yeah, my curiosity is what variables would impact the presence/absence of that white spot. Motion’s clearly an issue here, as you note, and speed could prove an interesting variable.
June 30th, 2009 at 12:54 am
I have a congenital eye disorder that effectively blinds my right eye. Normally most optical trickss (other than 3D) work for me (spinning disks, grey spaces on a grid). I wanted so bad to see his head disappear but it seems like a stereo vision trick to me. I’m always suspicious when they ask me to cover one eye, especially my blind one.
June 30th, 2009 at 1:05 am
It would be good if Richard could do a version with the right eye open instead of the left, as I have retina damage in my left-eye, so no good for me!
June 30th, 2009 at 1:32 am
You could turn your monitor upside down, Andy C.
June 30th, 2009 at 6:25 am
Great illusion. I’ve got good peripheral vision, so I could really see his body with no head.
Evil twin: good. Evil twin with a British accent: even better.
June 30th, 2009 at 6:27 am
Andy C. — if you download the video, maybe there’s a way to reverse the image.
June 30th, 2009 at 12:38 pm
Worked for me and I’m right hand / left eye dominant. If people don’t have a way to reverse this video and don’t have vision in their left eye why not just do exactly the same thing with their right eye but to a point off the left side of their monitor? There isn’t anything magical about looking at the ‘x’ in the video it is just that the guy’s head has to be in your blind spot.
June 30th, 2009 at 2:31 pm
[...] June 30, 2009, 3:30 pm Filed under: Bad Astronomy, Humor, Phil Plait, Science, YouTube Via Phil Plait, a delightful [...]
June 30th, 2009 at 2:31 pm
I’m pretty amazed at all the wonder and skepticism on this thing. I learned about the blind spot in elementary school. I mean, you can do the same thing with two fingers, making one fingernail disappear, almost anywhere. Like the demonstration in the video, if you vanish a fingernail, then move that finger upward until the nail emerges from the top of the dead zone, your whole finger appears, not a finger with a hole. It’s fun to play with, and has been since grammar school.
There’s another thing I’ve always noticed. If I’m looking at a star or planet, I can actually see it much better if I look JUST off to the side of it. I wonder if it has something to do with my blind spot. (No, I don’t have cataracts.)
June 30th, 2009 at 3:56 pm
DaveS,
When I was an amateur astronomer we used a similar technique called “averted vision”. The explanation given was that the rods and cones off centre in the eye were more sensitive than those that typically receive more light.
William Hyde
June 30th, 2009 at 8:34 pm
Didn’t work for me at all. Hrmm.
July 6th, 2009 at 12:37 pm
[...] pagina en een rondje links, maar Richard Wiseman heeft er een originele variant op gevonden. Bron: Bad Astronomy + [...]