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sidmel
2005-Nov-04, 03:05 PM
Pretty Nifty.

The Illusion (http://www.patmedia.net/marklevinson/cool/cool_illusion.html)

:eek:


EDITED by moderator ToSeek to fix link.

sarongsong
2005-Nov-04, 04:34 PM
Wow---could that explain pink elephants and green eggs?

Titana
2005-Nov-04, 05:08 PM
Wow that is kind of strange! There is some more very interesting optical illusions on this page www.michaelbach.de/ot/

I found them very interesting.


Titana.........

TheBlackCat
2005-Nov-05, 05:14 AM
I couldn't stay focused long enough for them all to disappear, but some did.

beskeptical
2005-Nov-05, 07:20 AM
That is pretty cool. I think I know how it works but I'd be interested in feedback.

The rod cells in the retina see red or green so I'm guessing when they fire off a red (pink in this case) signal to the brain they have a period of time where they have to reset their positive and negative potential (sodium and potassium). During that time the nerve is stimulated to fire but either it doesn't fire or it fires a weaker impulse. (That I'd have to look up, exactly how we see red or green with the same receptor since I don't remember the details.) As to some of the pink dots disappearing, the nerves firing off the signals get attenuated and ignore the stimulant.

I forgot to add, when you look in the center the light reaches the same nerves. When you follow the dots with your eyes you use different nerves constantly so the effect does not happen.

JohnD
2005-Nov-05, 10:50 AM
Here's an extension of this illusion:
Look at the screen, but off-centre, outside the circle. One radius is a good distance.
The green dot appears and the purple ones disappear. Wait a little longer
Then move your gaze, back to the centre, and briefly a GREEN circle of dots appears, where the circle previously was in your gaze.
This also works if you look at the centre, then away.

But is this more sophisticated that the usual illusion of looking at a bright light and then away, to see a reverse colour image of the bright light?

Look at the grey background with a magnifying glass. You will see the lines, or dots of black, green, red and purple that are usual on a colour monitor. Now look at a purple dot on theillusion through your magnifyer. You will see that the purple dots are enhanced and the red and green diminished-what you would expect.
BUT! As the lead dot rotates around the circle, the illusion dot flashes GREEN! You can't see this naked eye, as you perceive the equal intensity green and purple as background-grey. The purple illusion dots persist for longer than the green flash, so those receptors in your retina fatigue. You are left seeing dim greens and fatigued purple: equals background-grey! The rotating green dot is still seen, but it was there all the time!

I am not convinced, however, that this is fatigue of colour receptors, as the purple and green dots are not that bright. I suspect that this effect is more to do with our brain's ability to perceive a colour as the one we expect, rather than that due to the light frequency received. Look at a colour magazine in the light of sodium street lamps - your eyes are receiving pure sodium light, almost a single frequency, but you still 'see' the colours on the page, more or less.

This is a very clever illusion, that plays with our brains!

John

Planetwatcher
2005-Nov-05, 03:25 PM
Kewl.

Big Brother Dunk
2005-Nov-10, 10:32 PM
Hey, cool!

Stregone
2005-Nov-10, 11:03 PM
No its definitly the image burn-in/fatigue effect. If you pay attention after staring at the circle and move your gaze somewhere else you can see a whole ring of green dots.

TheBlackCat
2005-Nov-11, 02:23 AM
We just covered optical illusions in class today. The professor took the old "object in the foreground" position for the size of the moon illusion. I corrected him (that sort of thing is acceptable in this class if done politely and not too often), but I didn't press the issue.

Anyway, here are a couple of other very good illusions (all hosted by me)
http://img.photobucket.com/albums/v89/toddrme/shadow.jpg
http://img.photobucket.com/albums/v89/toddrme/opticalillusion.jpg
http://img.photobucket.com/albums/v89/toddrme/spinthing.jpg
The last one is so convincing I converted it to a jpg to prove it isn't animated. This one was actually shown in class, apparently it is a higher-level illusion (effecting more advanced stages of the visual cortex), and they think it has to do with the constant, random eye movements that the humane eye carries out but that you don't normally notice.

George
2005-Nov-11, 02:47 AM
Very cool, sidmel.

I noticed that as I glanced away, after all the effects were complete, I saw the dots as all green in the same circular pattern. From this, can we say the residual image of pink, which is the green, becomes strong enough after about 15 or 20 seconds (hang in there a little longer BlackCat ), to cancel out the pink completely? Like adding +1 to a -1 and getting 0. This is also supported by the fact there is no green dot other than in our minds.

This is in line with the idea beskeptical presented, I think. There is enough time delay action to allow this cancelation. If the dot were slower, it probably would not work.

beskeptical
2005-Nov-11, 07:22 AM
We just covered optical illusions in class today. The professor took the old "object in the foreground" position for the size of the moon illusion. I corrected him ...I'm confused here. The Moon looks bigger next to objects near the horizon because we interpret the size of it based on our brain's calculation of its position. So what was it your professor was saying?

BTW, I found an interesting test of that illusion. If you cover one eye and look at the Moon on the horizon, it immediately looks smaller.

Candy
2005-Nov-11, 07:33 AM
http://img.photobucket.com/albums/v89/toddrme/shadow.jpg
"A Thousand Pardons" started a thread about this illusion on the BABB some moons ago.

Dang, I'm still seeing green circles.

TheBlackCat
2005-Nov-11, 07:36 AM
I'm confused here. The Moon looks bigger next to objects near the horizon because we interpret the size of it based on our brain's calculation of its position. So what was it your professor was saying?

BTW, I found an interesting test of that illusion. If you cover one eye and look at the Moon on the horizon, it immediately looks smaller.
Well, according to the BA book the moon illusion is due to the way we percieve the shape of the sky. He says we percieve it as a bowl, with the top closer than the sides. In this scenario the moon looks bigger because we percieve it as being farther away. Farther objects are percieved as larger than nearby objects that are the same size on our retina.

JohnD
2005-Nov-11, 04:06 PM
George,
Someone else above you in this thread said that "there is no green dot" and I let it pass, but you have repeated it. Sorry, but you're wrong!

As I suggested, look at the screen closely with a magnifyer, strong enough to seperate the lines on the screen into their different colours. You do need a strong lens, so thatyou are seeing only a fraction of the dot! As the dot comes around, the green lines briefly flash, as bright as the purple lines. Seen naked eye, the purple dot disappears as green plus purple makes a grey dot, same as the background. A brighter grey dot but still grey! This effect is spoiled if you can seperate the lines by magnification.
The trick would not work if it was replaced by small light bulbs on a black background. That's one reason why I say it plays with our minds - we think the background is neutral, but it is an integral part of the illusion.

BC,
That pattern of chequered circles is interesting, for what it doesn't do for me. Looking at it, I can see the outer circles, outside my central visual area appear to rotate, but quickly to slow down and stop. Moving my gaze to another point starts them again, briefly. And the effect grows less as I am further away from the screen. Do others find the same?

Presumably, it is receptors in the retina outside the fovea, that produce this effect. These receptors are sensitive to movement more than shape, an evolutionary adaptation that provides a wider field of view to potential danger. This must be overridden by small regular patterns, as irregular ones such as a pattern of branches or grass blades does not appear to move.

John

sidmel
2005-Nov-11, 04:35 PM
An experiment that somebody with a color printer could explore, would be to print it out and see how the illusion works. I'm at work now and don't have access to one.

TheBlackCat
2005-Nov-11, 05:31 PM
George,
Presumably, it is receptors in the retina outside the fovea, that produce this effect. These receptors are sensitive to movement more than shape, an evolutionary adaptation that provides a wider field of view to potential danger. This must be overridden by small regular patterns, as irregular ones such as a pattern of branches or grass blades does not appear to move.

John
Receptors are not sensetive to motion. Ganglion cells are (specifically M-ganglion cells), but they occur all over the eye. If they were what was causing this, it wouldn't be so interesting. But PET scans show that this illusion does not trigger the first stage of the visual cortex processing (the V1 or primary visual cortex), which is driectly innervated by the M-cell pathway (known as the magnocellular pathway). Instead, it triggers a much higher-level visual processing area known as V5 (the fifth visual cortex).

George
2005-Nov-11, 06:16 PM
George,
Someone else above you in this thread said that "there is no green dot" and I let it pass, but you have repeated it. Sorry, but you're wrong!
Your argument should be extended to the presenters. They state it is not there.


There really is no green dot, and the pink ones really don't disappear


As I suggested, look at the screen closely with a magnifyer, strong enough to seperate the lines on the screen into their different colours. You do need a strong lens, so thatyou are seeing only a fraction of the dot! As the dot comes around, the green lines briefly flash, as bright as the purple lines.
It sure looks like you are right, JohnD. However, is it live, or is it Memorex? By blocking out all but one dot, when the pink disappears, I see a green dot. I suppose a filtered photometer might help. :)

I wonder if this illusion is applicable to the BA's interesting observation of a green Betelgeuse. (http://www.bautforum.com/showthread.php?t=34478)?

ranugad
2005-Nov-11, 08:12 PM
I love these kinda things, so I downloaded the .gif and played it.
12 frames. each frame has one dot missing, that's all.
The green dot HAS to be a residual image.
I increased the view to 2,000% with no other colors besides the grey background and purple shades.

So just for kicks I made one of my own to see if I could get the same effect without additional colors, besides the main dot color and background shading.

Here it is.
One dot doesn't disappear. I somehow lost a frame and my skill isn't good enough to fix it without starting from scratch.


http://members.aol.com/ranugad62/newer.gif

George
2005-Nov-11, 08:47 PM
:clap: I see gold! Pretty neat.

JohnD
2005-Nov-11, 10:10 PM
Well done, ranugad!!

Indeed, I see a gold dot rotating around and briefly replacing the blue. Then using my strong lens, I can see the individual pixels of my screen, and lo! they are blue, BUT as the dot comes around, I see the line of red and yellow pixels flash on and off (red +yellow=gold), while the blue pixels disappear. There IS a gold dot and the Blue dots DO disappear!

Thank you, george, for repeating my experiment - good scientific practice eh? I'm only reporting what I see, and you confrim my findings. So the caption on the original illusion page is misdirection, that any good magician uses. We KNOW their tricks are not magic, but tricks, and so is this. And a very good one.
What do you mean by "Memorex"? The only Memorex I know of was a brand of recording media.

I suspect that we may be talking about chalk and cheese. I have a hidef LCD screen - what's your's? This may be why we see differences through the magnifyer.

BC,
Thank you for those details! I did know that processing goes on in the retina, and was remiss in attributing it to the receptors. But these illusions really do play with our brains (delete, visual cortices!), don't they!

No one has answered my question about the duration of the motion effect. How long does it last for you?

John
John

George
2005-Nov-11, 10:45 PM
What do you mean by "Memorex"? The only Memorex I know of was a brand of recording media.
Yes, it is now an old saying, which makes me....:(. It was suggested it was impossible to tell audio quality between real live audio vs. Memorex's ability to reproduce it. We can't tell the difference wether or not the green is really there or not.

The green, and now ranugad's gold, will be seen as green no matter what we do (short of a photometric device). Since it was pink, as soon as it is turned off, our eye will register green. The green is only in our minds, or retinex, as some like to call it (short for retina/cortex).

ranugad's experiment verifys this idea as he does not add a gold dot to the action.

genebujold
2005-Nov-12, 12:07 AM
Pretty Nifty.

The Illusion (http://www.patmedia.net/marklevinson/cool/cool_illusion.html)

:eek:


EDITED by moderator ToSeek to fix link.

Thanks! I'll be able to use this in my upcoming divorce hearing. It appears my wife "saw" several things which absolutely did not happen. She has absolutely no evidence that it happened, but now I have evidence as to how she might have seen something that never existed!

Cudos...