Help: Optical Illusion Insight

[Normal Dude]

Fine idea. Professor Adelson agrees with me, and states, for the record,

Fine then. I am standing by my definition of it as an optical illusion in that the process leads to a misleading appearance, namely that the two tiles are different shades when in fact they are the same.

 

[robinson]

That takes us into philosophy of science, and perception itself, which is a cool subject as well.

Of course my use of the word "mind" may be a stumbling block, one neatly sidestepped by using the term "visual system".

I'm short of time these days, but I whipped out a quick example, before I read his explanation page, so I should post it, other wise I wasted a half hour on it.

To start, the picture below is of a white house, slight overcast, so there are no direct shadows, but plenty of differences in ambient light.

We have to accept, for this illustration, that it is indeed just a regular photo of a regular house, painted a shade of white. Based on what we know of the world and vision, we know it is all the same shade, even when in shadow,

Now I take a few clips of the actual shades, compare them with different backgrounds, and we can see how different the color really is.

1,2 and 3 are marked, so you can easily see the source.

In creating this example, I accidentally created another illsuion. The corner of the house, marked with an A, is perfectly vertical in the original photo, as well as my manipulation example.

Note the illusion, when the same image is placed next to itself. This is the same illusion that won illusion of the year, last year I believe.

Is it an illusion? The perception that the two houses in the second picture are tilted away from each other? I would say yes.

But the perception of the house as being all one color, is just normal operating procedure for making sense of the world.

Now, if somebody painted a house different shades of white, to simulate shadows, so we thought we were seeing a white house, with the normal shadows, when in fact it was really 12 shades of white and gray, that would be a cool illusion.

 

[Zeuzzz]

I have seen that illusion before (the one in the OP), and it reminds me of a weird effect that I discovered a few years ago that anyone can easily do. It makes me wonder how much of what we see with our eyes is what is 'actually' there, and how much of the information is filled in by our own brains.

Take an object, any object no bigger than a few cm (I use a rubber for example) and place it on a surface that is smooth and a constant color, ie, a table. Make sure that there are no other objects near the item, and look at it from an angle of about 45 degrees from a distance of about 1-2 foot or so. Now choose a small point about 5 - 10 cm above the object that you can clearly focus on, draw a small dot or someting. If you are able to keep your eyes still, and really focus on this small point hard, the object will start to become blurry in your peripheral vision. Eventually, and it usually happens quite suddenly, the object will seemingly dissapear completely from the table. Its very hard to maintain this for long, because as soon as it disappears you are tempted to look at it, and as soon as you move your eyes it will instantly reappear. I have shown many people this, most seem able to do it. Give it a go, it is pretty wierd if you can do it. I have been able to make some pretty large things disappear from my vision, but it always requires an object against a uniform color background, and the flatness of the surface seems to help aswell.

What do you think is occuring here? I'm pretty clueless about biology past GCSE level, and have always wondered why this occurs.

 

[robinson]

What do you think is occuring here? I'm pretty clueless about biology past GCSE level, and have always wondered why this occurs.

First thing I thought of was inattentional blindness.

Check it out, this stuff is real interesting.
http://viscog.beckman.uiuc.edu/djs_lab/demos.html
http://en.wikipedia.org/wiki/Inattentional_blindness

 

[Normal Dude]

I have seen that illusion before (the one in the OP), and it reminds me of a weird effect that I discovered a few years ago that anyone can easily do. It makes me wonder how much of what we see with our eyes is what is 'actually' there, and how much of the information is filled in by our own brains.

Take an object, any object no bigger than a few cm (I use a rubber for example) and place it on a surface that is smooth and a constant color, ie, a table. Make sure that there are no other objects near the item, and look at it from an angle of about 45 degrees from a distance of about 1-2 foot or so. Now choose a small point about 5 - 10 cm above the object that you can clearly focus on, draw a small dot or someting. If you are able to keep your eyes still, and really focus on this small point hard, the object will start to become blurry in your peripheral vision. Eventually, and it usually happens quite suddenly, the object will seemingly dissapear completely from the table. Its very hard to maintain this for long, because as soon as it disappears you are tempted to look at it, and as soon as you move your eyes it will instantly reappear. I have shown many people this, most seem able to do it. Give it a go, it is pretty wierd if you can do it. I have been able to make some pretty large things disappear from my vision, but it always requires an object against a uniform color background, and the flatness of the surface seems to help aswell.

What do you think is occuring here? I'm pretty clueless about biology past GCSE level, and have always wondered why this occurs.

I believe, if I am reading the description correctly, that this is demonstrating that 1. Your retina is a detector of change and 2. peripheral vision sucks . Keeping your vision fixated on something else keeps the object at the same point on your retina and it fades from view without new information. This happens because there are less cells in the peripheral portions of your retina that respond in a sustained fashion to a stimulus, as opposed to transient cells that respond to changes in stimulus. Your eyes do tremor constantly (random small movements), but in peripheral vision the tremor may be smaller than the receptive fields of the cells, so in effect for those cells the tremor doesn't make any difference.

 

[Gregory]

If someone could explain this to me, I'd be very appreciative; it's incredibly striking.

 

[robinson]

If someone could explain this to me, I'd be very appreciative; it's incredibly striking.

You see a ghostly reverse image of whatever you stare at, due to chemical processes in your receptors. In your example, it looks like this,

but because it is only in your eyes/optical system, it moves a bit, and is blurred, but the same thing happens with any contrast object you stare at.

In this example, the off kilter stuff, which was put there, and prevents you from seeing the image in the negative original, is ignored when you "see" the after image, because our brains ignore information, as well as add stuff to what we see, so that it makes sense.

You can see this by squinting or blurring that image, it quickly is resolved and we see a man with a beard and long hair.

 

[robinson]

ITake an object, any object no bigger than a few cm (I use a rubber for example) and place it on a surface that is smooth and a constant color, ie, a table. Make sure that there are no other objects near the item, and look at it from an angle of about 45 degrees from a distance of about 1-2 foot or so. Now choose a small point about 5 - 10 cm above the object that you can clearly focus on, draw a small dot or someting. If you are able to keep your eyes still, and really focus on this small point hard, the object will start to become blurry in your peripheral vision. Eventually, and it usually happens quite suddenly, the object will seemingly dissapear completely from the table. Its very hard to maintain this for long, because as soon as it disappears you are tempted to look at it, and as soon as you move your eyes it will instantly reappear. I have shown many people this, most seem able to do it. Give it a go, it is pretty wierd if you can do it. I have been able to make some pretty large things disappear from my vision, but it always requires an object against a uniform color background, and the flatness of the surface seems to help aswell.

What do you think is occuring here? I'm pretty clueless about biology past GCSE level, and have always wondered why this occurs.

Wow. I did several experiments and you are correct, and that is really freaky man. It is hard not to move the eyes, especially when it first starts getting blurry, and then when it seems to vanish, it is really hard not to change the eyes, the slightest movement and the object pops back in, full focus.

Wow. I can't believe I have never heard of that before, much less never noticed it happening. If you hadn't mentioned it, I would probably never have noticed that effect at all. Now that I am aware of it, I can't not notice it happening. I couldn't get it to work unless the object was in the foreground.

In low light, I was able to observe it with even a large object. That is really freaking cool, and I have no idea why it happens. As far as I know, nobody has ever published that little optical phenomenon before.

Did you discover it? That is one of the coolest things I have learned in a while. Thanks. I hope some other people will try it. That could be an entire topic.

 

[alfaniner]

...
Take an object, any object no bigger than a few cm (I use a rubber for example) ...

I assume you either left out the word "ball", are using the term differently than we in the U.S. do (perhaps referring to what we would call an "eraser"?), or are using a really small one.

 

[Professor Yaffle]

If you press gently on your eyeball at the side (sort of through the eyelid) to keep it still, and close the other eye, after a few seconds your vision begins to 'grey out' starting at the periphery.

 

[rjh01]

Words of wisdom from Scientific American.
I have heard people suggest that the people who apply for the MDC may be Schizophrenic. I think a good question to ask them would be about optical illusions. They do not get fooled by them as much as ordinary people.

Source http://www.sciam.com/article.cfm?id=schizophrenics-better-at

Why do they work?

[Many] optical illusions may work not by deceiving our visual system, as long suspected, but rather by making visible a natural contention between the two hemispheres of the human brain. If Pettigrew's theory is correct, then the reason an optical illusion such as the Necker cube outline, which seems to turn inside out periodically, works is that, in some deep biological sense, you are of two minds on the question of what to see.

See http://www.sciam.com/article.cfm?id=side-splitting

 

[Jeff Corey]

If you press gently on your eyeball at the side (sort of through the eyelid) to keep it still, and close the other eye, after a few seconds your vision begins to 'grey out' starting at the periphery.

The stabilized retinal image eliminates the usual saccades that normally keep refreshing the image. You can eliminate the effect by blinking.
According to this article, it is not simply due to adaptation, but our old friend lateral inhibition is also involved. http://www.visualpathways.com/stabilized.html

 

[Zeuzzz]

I assume you either left out the word "ball", are using the term differently than we in the U.S. do (perhaps referring to what we would call an "eraser"?), or are using a really small one.

Yes, I meant eraser, I could have chosen a better object/word than that

Wow. I did several experiments and you are correct, and that is really freaky man. It is hard not to move the eyes, especially when it first starts getting blurry, and then when it seems to vanish, it is really hard not to change the eyes, the slightest movement and the object pops back in, full focus. [...]

Did you discover it? That is one of the coolest things I have learned in a while. Thanks. I hope some other people will try it. That could be an entire topic.

Yeah, I was at really bored in a lesson at college and I noticed that when you focus your attention on a particular spot for a long time a lot of your peripheral vision gets blurry, and as I was doing it my textbook suddenly vanished from the table! I was quite surprised to say the least.

You can make things appear blurred by focussing on just about anything at any distance, but it seems that you can only get object to completely disappear under a few specific conditions.

I used to try to make my tutor to dissappear against the large white board he was stood infront got pretty close a few times, but never got it completely.


And this slightly different illusion is a clip that I found on youtube, its really cool, tests your inattentional blindness.

In this video two groups of people are passing a basket ball to each other. You should focus your attention on the people in white t-shirts. Try to count how many times the ball is passed between them during the video. This can be a bit tricky as the other group, in black t-shirts, must be ignored.

And another similar one here;




Doesnt work for eveyone, but when it does its quite amazing.

 

[robinson]

Oh yeah. Every time consider starting a topic on that, the issue of how not to spoil it comes up.

 

[Professor Yaffle]

This one is amazing. Stare at the centre of the picture from about a metre away and after a while you will suddenly see a giraffe.

 

[arthwollipot]

That one keeps on getting funnier every time I see it...

 

[alfaniner]

Here's another take on that basketball video (the original version keeps getting deleted from YouTube, but this source is better anyway).

 

[robinson]

I think it is wild that somebody made a commercial using that. The originators have been very protective of the original footage. Then the same concept shows up on the telly.

Either way, a very interesting concept, that inattentional blindness. It explains a lot of things, including some terrible accidents.

 

[Skeptic Ginger]

I was in the back seat of a car, my friend driving got into the left turn lane and was going pretty slow so I thought he saw the guy on the motorcycle coming the other way until my friend turned in front of the guy. I am so careful now looking for things when I am turning. I'm convinced there will be things you are looking right at and can't see.

So was there a tap dancing monster? Or is that just the big stomper at the end?

 

[DevilsAdvocate]

Then, eventually, the pseudo-green becomes fatigued, and you are left with the neutral gray of the background, which is why they seem to disappear.

Is this what really happens? It doesn't seem to be the case.

The animation consists of 12 frames. In each frame, one of the 12 purple dots is removed; it is replaced with a gray background the same as the rest of the gray background. The dots are removed in clockwise order.

When viewed from far away, the animation appears to be what it is. But up close, the removed dot appears as a green dot.

When you fix your stare at the cross, you see the circle of purple dots. But as each dot is removed, you see a green dot flash and then the dot is gone completely (it is gray like the background) until the full circle is completed and you just see a single green dot flashing in a circle and no purple dots at all.

The reason you see a green dot, when there is actually no dot, is because of the burn from the purple dot. You see the inverse color. But then why do the dots seem to disappear completely? It doesn’t seem that the pseudo-green becomes fatigued because I continues to see a single green dot spinning in a circle. Also, when I have it set to where I only see a single green spinning in a circle and then move my vision to a white surface, I see a circle of green dots on the white surface.

So, is it possible that I am simultaneously seeing the actual purple dot plus the green burn-in which combines to be gray? In that case, I would be seeing a full circle of pseudo-green dots, which matches what I see when I look away, plus a full circle of purple dots (minus the removed dot), which matches what is actually there, and a single pseudo-green dot at the place where the purple dot was removed, which matches how the animation appears to me.

1) Is that what is happening?

Also, if I stare directly at a single purple dot, I see the other purple dots disappear, but the dot I’m staring at remains. So I see the one purple dot, with a green dot that travels around the circle and replaces the purple dot when it gets to that position.

2) Why doesn’t the purple dot disappear like the rest?