Neat optical illusion

[Forty-Two]

This was listed on FARK.com a few days ago as "The coolest trick you'll play on your brain today." It's a great optical illusion; I hope you enjoy it as much as I have.

http://www.johnsadowski.com/big_spanish_castle.html

(Note: It works best if you follow the directions; I swear it's not one of those "crazy, scary-looking image jumps out at you" tricks.)

[tkingdoll]

Whoa! That totally rocks!

It only stays in colour for a split second for me, even if I don't move my eyes. Or maybe I'm moving them without realising. Either way, that's ace.

[Meffy]

Pretty good, reminds me of the reverse-color US flag projection trick. :-)

Here's the most jawdropping animated GIF I've ever seen.

http://vygotsky.sfasu.edu/Courses/psy133/rotate_circles.jpg

The amazing part is that it's not animated. Let your gaze wander around the pattern and see the "snakes" slowly turn while not moving at all. I can't resist seeing motion even while knowing perfectly well that it's static. Can you?

[edit] Here's the parent page: http://vygotsky.sfasu.edu/Courses/psy133/illusions.html

[tkingdoll]

Pretty good, reminds me of the reverse-color US flag projection trick. :-)

Here's the most jawdropping animated GIF I've ever seen.

http://vygotsky.sfasu.edu/Courses/psy133/rotate_circles.jpg

The amazing part is that it's not animated. Let your gaze wander around the pattern and see the "snakes" slowly turn while not moving at all. I can't resist seeing motion even while knowing perfectly well that it's static. Can you?

[edit] Here's the parent page: http://vygotsky.sfasu.edu/Courses/psy133/illusions.html

I can get one to stay still if I focus on the dots, but the ones in my peripheral vision still spin. I love this sort of thing. Richard Wiseman did a great presentation of visual illusions at TAM4, totally worth seeing.

[Meffy]

For me, as long as I don't look at one place for more than a couple seconds, the wheels whirl. I can't figure how it does that. I think I understand how the trick in the OP works -- overlays an after-image (in reverse color, as they are) upon a grayscale image. Very clever, so dramatic!

Did Wiseman's presentation touch on the problems with eyewitness accounts? Tricks of motion and geometry that make Venus seem to dash around like an alien recon ship, that kind thing?

[Floyt]

:hypnotize wrrglll...

[alfaniner]

OK, whenever this subject comes up I always like to bring out this one. Look closely and note which side has the angry face.

Then, squint (or view at a distance) and see what happens!

http://forums.randi.org/imagehost/171448f6cfc93a73.jpg

First found on Ian Rowland's pages.
Ian Rowland illusion page (http://www.ianrowland.com/MiscPages/Mrangryandmrscalm.html)

[Taffer]

This was listed on FARK.com a few days ago as "The coolest trick you'll play on your brain today." It's a great optical illusion; I hope you enjoy it as much as I have.

http://www.johnsadowski.com/big_spanish_castle.html

(Note: It works best if you follow the directions; I swear it's not one of those "crazy, scary-looking image jumps out at you" tricks.)

:D Very cool!

[Zep]

Love this stuff! Keep it up!

PS. We should post it on the homeopath forums, and see if they get freaked by it. You know - things appearing to be what they are not, and all that...

[This Guy]

Cool indeed!

I love this stuff :)

[richardm]

Hmm, I saw the castle one the other day and couldn't make it work. Perhaps the server was being hammered and I wasn't allowing time for the second image to load. It certainly works now :)

This is a pretty nice one (also from the link above, in fact)

http://img.photobucket.com/albums/v507/richardm/dotillusion.gif

[Tirdun]

Hmm, I saw the castle one the other day and couldn't make it work. Perhaps the server was being hammered and I wasn't allowing time for the second image to load. It certainly works now :)
This is a pretty nice one (also from the link above, in fact)


:exeyes:

[Paul C. Anagnostopoulos]

It only stays in colour for a split second for me, even if I don't move my eyes. Or maybe I'm moving them without realising. Either way, that's ace.
Stare at the dot longer.

Hey Ian! This one's cool!

~~ Paul

[tkingdoll]

Stare at the dot longer.

Hey Ian! This one's cool!

~~ Paul

I fear for my already fragile eyesight :D

Talking of which, stare at my avatar for a few moments and you'll get a nice surprise!

[CFLarsen]

Very cool!

But, I still think Adelson's grey checkerboard (http://www.youramazingbrain.org.uk/supersenses/adelson.htm) is the most amazing optical illusion.

Hey, Ian! Do you still thing the two grey squares are not the same shade of grey? :)

[tkingdoll]

Very cool!

But, I still think Adelson's grey checkerboard (http://www.youramazingbrain.org.uk/supersenses/adelson.htm) is the most amazing optical illusion.

Hey, Ian! Do you still thing the two grey squares are not the same shade of grey? :)

Agreed, I really like that one. A proof can be found here: http://img69.imageshack.us/img69/8523/chess5vo.jpg - the B square has been cut out and moved next to the A square.

[Ladewig]

Good stuff.

[richardm]

Stare at the dot longer.

Also, if you've stared adequately long at the dot and then look at a different part of the image then the colours do disappear; but looking back at the dot makes the colours fade back in. It's very strange, I love it!

[malaka]

Very cool!

But, I still think Adelson's grey checkerboard (http://www.youramazingbrain.org.uk/supersenses/adelson.htm) is the most amazing optical illusion.


Agreed. And followed closely by the Dragon Illusion (http://www.grand-illusions.com/opticalillusions/dragon_illusion/). I have one of these atop my cube entrance at work.

[bmillsap]

But, I still think Adelson's grey checkerboard (http://www.youramazingbrain.org.uk/supersenses/adelson.htm) is the most amazing optical illusion.

This has always been my favorite, the one I (and everyone else I show it to) consistently just can't believe is true, but there it is.

[Meffy]

Hey, Ian! Do you still thing the two grey squares are not the same shade of grey? :)
Did he deny it even after being shown the truth? Did he try chopping out a bit of square A in a graphics program and dragging it over B? :-D

I find the people who most vehemently defend indefensible positions are usually those least willing to try simple experiments for themselves -- experiments that would quickly demonstrate what's going on.

[Hellbound]

Meffy:

IIRC, his actual argument, after getting past the "I'm right because you're all idiots!" stage, was that color is, specifically, what the brain interprets, and not what is actually there.

Thus, to him, it really is a different shade until you move it.

[tkingdoll]

Meffy:

IIRC, his actual argument, after getting past the "I'm right because you're all idiots!" stage, was that color is, specifically, what the brain interprets, and not what is actually there.

Thus, to him, it really is a different shade until you move it.

Or, he couldn't believe it was different, tried it in Photoshop, realised he was wrong, but had gone too far to back down so invented a ridiculous argument to try and support his ailing position?

[tsg]

Or, he couldn't believe it was different, tried it in Photoshop, realised he was wrong, but had gone too far to back down so invented a ridiculous argument to try and support his ailing position?

[heavy sarcasm]That doesn't sound like Ian.[/heavy sarcasm]

[Hellbound]

Or, he couldn't believe it was different, tried it in Photoshop, realised he was wrong, but had gone too far to back down so invented a ridiculous argument to try and support his ailing position?

Not Ian! HAven't you heard? He's the only person that never lies and is always right, so you obviously must be incorrect.

;)

[Mercutio]

Or, he couldn't believe it was different, tried it in Photoshop, realised he was wrong, but had gone too far to back down so invented a ridiculous argument to try and support his ailing position?
Ian's argument was consistent with his position in other threads. Huntsman pretty much got it.

From a materialist perspective, the job of science is to understand the discrepancy between what is observed, which changes, and what is physically there (which we define as "real"). From Ian's idealist perspective, the job of science is to understand the discrepancy between what is observed (which we define as "real") and what is physically measured (which may differ for stimuli which are observed to be the same). It is a perfectly good philosophical position from which to explore the same questions as science does when approached from a materialist view. The job of connecting "out there" with "in here" is the same; the axiomatic assumptions of "what is real" are different.

[Bob Klase]

This has been my favorite for a long time:

http://dogfeathers.com/java/spirals.html

There's a downloadable version here:

http://www.grand-illusions.com/pinwheel.htm

Binary arts used to make a metal disk that you could spin on a table with this on it. Haven't seen it for 5-6 years though so guess they stopped.

There's also some good ones here that he's gathered from other sites:

http://illusionsetc.blogspot.com/2004_12_01_illusionsetc_archive.html

[alfaniner]

Agreed. And followed closely by the Dragon Illusion (http://www.grand-illusions.com/opticalillusions/dragon_illusion/). I have one of these atop my cube entrance at work.

YouTube had a very popular video of that illusion on its "Most Viewed" for some time. It might still be on the site if you search for it.

[malaka]

YouTube had a very popular video of that illusion on its "Most Viewed" for some time. It might still be on the site if you search for it.

A video of the illusion is also included on the site, itself. Check http://www.grand-illusions.com/images/articles/opticalillusions/dragon_illusion/dragon_illusion.wmv

[Overman]

So cool.:cool:

Give me more!!!:hypnotize

[Paul C. Anagnostopoulos]

From a materialist perspective, the job of science is to understand the discrepancy between what is observed, which changes, and what is physically there (which we define as "real"). From Ian's idealist perspective, the job of science is to understand the discrepancy between what is observed (which we define as "real") and what is physically measured (which may differ for stimuli which are observed to be the same). It is a perfectly good philosophical position from which to explore the same questions as science does when approached from a materialist view. The job of connecting "out there" with "in here" is the same; the axiomatic assumptions of "what is real" are different.
I basically agree, but things get sticky when "what is observed" changes as we vary the observing apparatus (senses), because it is not clear where the boundary between the observer and the observed lies.

For example, consider the "deepest" part of my visual mechanism, the part that is fooled by the checkerboard illusion. According to Ian, that deep mechanism is part of the observed, not the observer. But would you call it part of the stimuli of the illusion? Tricky, that.

~~ Paul

[Meffy]

Thanks to all for the clearing-up. Ian's world certainly is... erm... interesting.

[Forty-Two]

That dragon illusion is awesome. I printed out the PDF and made one of my own. Thanks for the link!

[Mercutio]

I basically agree, but things get sticky when "what is observed" changes as we vary the observing apparatus (senses), because it is not clear where the boundary between the observer and the observed lies.

For example, consider the "deepest" part of my visual mechanism, the part that is fooled by the checkerboard illusion. According to Ian, that deep mechanism is part of the observed, not the observer. But would you call it part of the stimuli of the illusion? Tricky, that.

~~ Paul
Actually, I think Ian has been quite consistent on that. The explanations for that illusion (as well as the Muller grid illusion) rely in part on the structure of perceptive fields in the retina, which (through a differential center/surround positive and negative feedback mechanism, which I can explain but which is not the point here) mechanically (close enough) makes edges more salient, makes colors dependent on their surrounding colors (where "color" is defined subjectively, not by wavelength), and can be modeled mechanically quite easily (probably already is being used in mechanical vision for robotic uses, but I don't know that--it is a tremendously useful little trick). Likewise, the spectral sensitivities of the alpha, beta, and gamma photopigments can also be modeled mechanically and used to describe how differing combinations of wavelengths can be associated with the exact same experienced color.

In both cases (receptive fields and trichromatic theory), the sensory apparatus mechanisms are part of the illusion (indeed, it would not happen without it); both are part of what Ian's ideal observer must experience. Both, to Ian, are part of the outside-of-observer, seemingly physical (although I think Ian would perhaps argue that we cannot assume they are physical, since the only evidence we have for them is experiential) world. Ian's observer is not dependent on such things, but on the experience itself.

It takes a great deal of effort to understand Ian, but I find it quite worth it. (I do not guarantee that my explanation is the same as his--some may be my interpretation of his view...also I am in a bit of a hurry right now, prepping for class.)

[alfaniner]

That dragon illusion is awesome. I printed out the PDF and made one of my own. Thanks for the link!

I'm working on doing one with an actual dog photo but need to get it just right.

[Dark Jaguar]

Neato supremo, but the dragon one doesn't really seem to have the effect it's going for. I can tell it's concave, and I think that's the problem. Another part of it is I was first exposed to this sort of illusion when I was like... 4 or something, so I think my brain adapted rather well.

The rest work great.

[luchog]

OK, whenever this subject comes up I always like to bring out this one. Look closely and note which side has the angry face.
If i look at it without squinting, they both look angry to me. But i have really bad eyesight, and my glasses tend to distort things a little.

[luchog]

I recall reading somewhere that some types of schizophrenics are not able to be fooled by some sorts of optical illusions. Something about the way their brain fails to filter then normally; which may be linked to the mechanism responsible for paranoia as well. I can't seen to find the study in my links.

[n11/n12]

Neato supremo, but the dragon one doesn't really seem to have the effect it's going for. I can tell it's concave, and I think that's the problem. Another part of it is I was first exposed to this sort of illusion when I was like... 4 or something, so I think my brain adapted rather well.

Try keeping one eye closed as you look at it.

[Dark Jaguar]

Considering it's a 2D image on my moniter... how exactly would that help? :D I'm merely saying that though I know the illusion is based on depth perception, in looking at it on my moniter the only depth can be provided by my brain's interpretation and not two viewpoints, so I doubt that my being able to see the actual depth perception was what threw it off. I just think it's the nature of how when something moves back and forth like that it immediatly jumps out at me as "concave", because it doesn't look right to my brain.

[Paul C. Anagnostopoulos]

In both cases (receptive fields and trichromatic theory), the sensory apparatus mechanisms are part of the illusion (indeed, it would not happen without it); both are part of what Ian's ideal observer must experience. Both, to Ian, are part of the outside-of-observer, seemingly physical (although I think Ian would perhaps argue that we cannot assume they are physical, since the only evidence we have for them is experiential) world. Ian's observer is not dependent on such things, but on the experience itself.
But then why does Ian insist that color is in the sensory apparatus rather than in the image? If both the sensory apparatus and the image are outside-of-observer, why argue so strongly for color being in one as opposed to the other? Neither are in the privileged position of observer, which I believe is where Ian wants color to lie.

Ian has said that the Metamind plays the external world on the senses of the observer. This makes it sound as if the senses are not part of the external world, are not outside-of-observer.

I remain confused.

~~ Paul

[Raphael]

Lots of fun- thanks 42

Adelson’s illusion (http://www.youramazingbrain.org.uk/supersenses/adelson.htm)- This really makes you think about how we interpret the outside world based on previous experience. I ended up making a template with the two squares cut out, and moving it about on my monitor trying to find positions where the shades matched and changed.

[tsg]

Lots of fun- thanks 42

Adelson’s illusion (http://www.youramazingbrain.org.uk/supersenses/adelson.htm)- This really makes you think about how we interpret the outside world based on previous experience. I ended up making a template with the two squares cut out, and moving it about on my monitor trying to find positions where the shades matched and changed.

This is what convinced me:
http://forums.randi.org/imagehost/59414490fc75975c9.jpg

The wierd thing is that when you use the color grabber on the B square, it still looks much darker.

[CFLarsen]

Did he deny it even after being shown the truth?

Ayup.

Did he try chopping out a bit of square A in a graphics program and dragging it over B? :-D

Nope.

I find the people who most vehemently defend indefensible positions are usually those least willing to try simple experiments for themselves -- experiments that would quickly demonstrate what's going on.

Ayup.

We should cherish Ian.

[CFLarsen]

But then why does Ian insist that color is in the sensory apparatus rather than in the image? If both the sensory apparatus and the image are outside-of-observer, why argue so strongly for color being in one as opposed to the other? Neither are in the privileged position of observer, which I believe is where Ian wants color to lie.

Why? Because Ian believes that he creates the world in his mind. We are all figments of his imagination.

Ian has said that the Metamind plays the external world on the senses of the observer. This makes it sound as if the senses are not part of the external world, are not outside-of-observer.

I remain confused.

~~ Paul

That's natural, when you are dealing with Ian..... ;)

[Dog Boots]

This is what convinced me:
http://forums.randi.org/imagehost/59414490fc75975c9.jpg

The wierd thing is that when you use the color grabber on the B square, it still looks much darker.

My living room walls are blue, sort of like the forum buttons blue. When I got my video projector, I installed it on a shelf on the wall, projecting on to the opposite wall. I then proceeded to paint the exact area of the projected image white, to function as a screen, but before I did that, I had no trouble convincing my brain, that the white parts of an image were really, completely white - even though they were really baby blue.

It's also amazing to watch something on there when the room is not darkened, and look how black the black parts of the image looks, but when you look at another part of the wall, which is white just like the screen - it looks white - not black.

Btw. that dragon is just creepy! I also made one myself (at 3:30AM over here) when I discovered it - and it's addictive! Highly recommended!

[El Greco]

An amazing such illusion appears in a BBC documentary about the brain. It's two girls in the same room, but one appears to be twice as big as the other. When they move next to each other you realize they are of the same height. The furniture and the walls in the room have been scaled so as to create that illusion.

[Paul C. Anagnostopoulos]

Why? Because Ian believes that he creates the world in his mind. We are all figments of his imagination.
No, I believe he thinks that the Metamind plays the external world on our senses (or something), so that the external world is a construct of the Metamind.

~~ Paul

[I less than three logic]

Did he deny it even after being shown the truth? Did he try chopping out a bit of square A in a graphics program and dragging it over B? :-D

No, no, no. That’s Cheating. :)

http://forums.randi.org/showthread.php?postid=1506305#post1506305

[ceptimus]

It comes down to whether you think the word 'color' refers to an intrinsic property of an object, or what is perceived by the mind. Ian uses the latter meaning, and his position seems logically consistent to me.

What color is a piece of white paper when there is no light? Ian would say (I think) that it's black - so paper stored in a lightproof box is black, and it only becomes white when you take it out into the daylight. It may seem like a strange way of considering things to most people, but I don't think that makes it wrong necessarily.

Another thing. In the case of the Adelson image, if you say that the image is a representation of a 3D scene, then the original 3D squares are indeed different colors - it is only on the 2D representation that they're the same - as one happens to be in shadow.

In the 2D representation, the 'squares' aren't actually square - so the fact that people refer to them as 'squares' should mean that they are referring to the 3D object represented. If you accept this, then Ian is right.

[Mercutio]

An amazing such illusion appears in a BBC documentary about the brain. It's two girls in the same room, but one appears to be twice as big as the other. When they move next to each other you realize they are of the same height. The furniture and the walls in the room have been scaled so as to create that illusion.
That is the classic Ames room. (http://www.psychologie.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/ames_room.html)

[Tirdun]

It comes down to whether you think the word 'color' refers to an intrinsic property of an object, or what is perceived by the mind. Ian uses the latter meaning, and his position seems logically consistent to me.
The interpretation of color is not the same as the inherent color of an item. A white piece of paper in no light is still white, it is never "black". If I put it under red lights it appears red, but it is still a white piece of paper because it reflects all available visible light in a diffuse pattern equally, which is the definition of white. Color is based on the physics of light, interpretation is based on how our brain works.
In the case of the Adelson image, if you say that the image is a representation of a 3D scene, then the original 3D squares are indeed different colors - it is only on the 2D representation that they're the same - as one happens to be in shadow.
It is a 2D image that we interpret as if it were a 3D scene. The interpretation changes the color in our mind, but nothing changes the fact that the two squares share the same color wavelength. Because it appears to be a 3D scene, our brain makes certain adjustments for the depth of the scene and apparent effect of the cylinder's (or what we perceive to be a cylinder) shadow.
if [...] Ian is right.
I disagree. If you change the visual input, the color interpretation will change, such as by blocking elements of the picture or overlaying a common color. I had to print the picture out to prove it to someone, using a fold. They were mostly convinced, but used the soft copy to check the actual color values in an editing program. Sometimes knowing an illusion is present will ruin the effect, but the cubes are so pervasive that we continue to believe, even if we know otherwise.

Regardless, our interpretation of what color the blocks are doesn't change the fact that they are, by definition, the same color.

[Mercutio]

Regardless, our interpretation of what color the blocks are doesn't change the fact that they are, by definition, the same color.
But that is precisely the point. Your (and most others) define "the same color" by reference to the physical properties. Yet one cannot deny that two different "surrounds" can make the same physically defined color appear to be two quite different colors. If our definition has as its bedrock the appearance of the color, then they are, by definition, not the same color, despite having the same physical properties.

The job of perceptual science (explaining the relationship of external stimulus to internal perception) remains the same; we are simply solving for a different variable. Metaphorically, instead of regressing perception onto stimulus, we are regressing stimulus onto perception. What Ian is doing here solves the same problem Fechner did over a century ago when he invented psychophysics.

Indeed, in some visual perception experiments, the task of the subject is to perform "color matching", in which two different mixes of wavelengths are manipulated until they appear to be the same color. This is perfectly good science, it gives us good data on the relative spectral sensitivities of the cone cells, and it does so by treating the perceived color as the standard.

I am not saying Ian's way is superior, merely that it is logically coherent and useful.

[tkingdoll]

But that is precisely the point. Your (and most others) define "the same color" by reference to the physical properties. Yet one cannot deny that two different "surrounds" can make the same physically defined color appear to be two quite different colors. If our definition has as its bedrock the appearance of the color, then they are, by definition, not the same color, despite having the same physical properties.

The job of perceptual science (explaining the relationship of external stimulus to internal perception) remains the same; we are simply solving for a different variable. Metaphorically, instead of regressing perception onto stimulus, we are regressing stimulus onto perception. What Ian is doing here solves the same problem Fechner did over a century ago when he invented psychophysics.

Indeed, in some visual perception experiments, the task of the subject is to perform "color matching", in which two different mixes of wavelengths are manipulated until they appear to be the same color. This is perfectly good science, it gives us good data on the relative spectral sensitivities of the cone cells, and it does so by treating the perceived color as the standard.

I am not saying Ian's way is superior, merely that it is logically coherent and useful.

My husband had an interesting response to the checkerboard illusion. I showed it to him, and the question underneath says "Are squares A and B the same shade of grey? "

His answer was no. I laughed, thinking he'd fallen for the obvious, and said "actually, they are the same", and showed him in Photoshop.

He replied "that's not what I meant. The question was are the squares the same shade of grey. They are not. In the checkerboard pattern, one is a light square and the other is a dark square. They have the appearance of being the same shade when you put them together because the B square has a shadow cast over it from the green cylinder. It's artificially the same colour as A but in the reality of the board, it is not".

[I less than three logic]

My husband had an interesting response to the checkerboard illusion. I showed it to him, and the question underneath says "Are squares A and B the same shade of grey? "

His answer was no. I laughed, thinking he'd fallen for the obvious, and said "actually, they are the same", and showed him in Photoshop.

He replied "that's not what I meant. The question was are the squares the same shade of grey. They are not. In the checkerboard pattern, one is a light square and the other is a dark square. They have the appearance of being the same shade when you put them together because the B square has a shadow cast over it from the green cylinder. It's artificially the same colour as A but in the reality of the board, it is not".
Yes, but that is the illusion. There never was a real checkerboard, this is not a photograph. It was drawn with the very intention of making square A and square B the exact same shade of gray, and simultaneously fooling the brain into believe they are different colors. You do not need to move the squares to make them appear the same color, only remove the other visual cues your brain is receiving from the picture.

One of the best ways to observer this is to print the picture, then with a separate piece of paper cut out two squares that will allow you to see only square A and B. Place the paper over the picture and the two squares are the same color, remove the paper and they look different again. It is your brain creating the difference in color. The artificial color created is not “a shadow on a light square making it appear as the same color as the dark square”, the artificial color is your brain’s interpretation that “it is a light square within a shadow, and therefore must be a different color from the dark square”. That is the illusion.

[tkingdoll]

Yes, but that is the illusion. There never was a real checkerboard, this is not a photograph. It was drawn with the very intention of making square A and square B the exact same shade of gray, and simultaneously fooling the brain into believe they are different colors. You do not need to move the squares to make them appear the same color, only remove the other visual cues your brain is receiving from the picture.

One of the best ways to observer this is to print the picture, then with a separate piece of paper cut out two squares that will allow you to see only square A and B. Place the paper over the picture and the two squares are the same color, remove the paper and they look different again. It is your brain creating the difference in color. The artificial color created is not “a shadow on a light square making it appear as the same color as the dark square”, the artificial color is your brain’s interpretation that “it is a light square within a shadow, and therefore must be a different color from the dark square”. That is the illusion.

Well, not necessarily. As I stated, I showed him the two squares together (I used Photoshop, see my link in an earlier post), but his point was that your brain identifies them as different because of your expection of the pattern of a checkerboard, so the 'reality' of the board is relevant.

What we don't know (yet, it's pretty easy to find out) is what colour square B is without the shadow. If it's the same as the light squares surrounding square A, then his point is valid.

[CFLarsen]

Deleted.

[Meffy]

[edit] Comments struck to avoid further Ianization of thread.

[Upchurch]

Did he deny it even after being shown the truth? Did he try chopping out a bit of square A in a graphics program and dragging it over B? :-D

I find the people who most vehemently defend indefensible positions are usually those least willing to try simple experiments for themselves -- experiments that would quickly demonstrate what's going on.
Some history (http://forums.randi.org/showthread.php?p=310465&highlight=Adelson#post310465)

[Meffy]

Thanks... *reads* *chokes* Just 52 pages? S'arright, I'll take the sampling as reprsentative and hope for the best.

[alfaniner]

Here's an interesting site on color perception. (Requires Java)
Color perception link (http://www.tsi.enst.fr/~brettel/DaltonDemo/DD08.html)

Normal sighted people are always surprised that the "Normal" and "Deutan" views are virtually identical to me, except perhaps for some shifts in contrast.

[roger]

Thanks... *reads* *chokes* Just 52 pages? S'arright, I'll take the sampling as reprsentative and hope for the best.His final position was reasonable - that they look different, but measure the same, and that when he uses the word color he is referring to the former.

The problem was that it went about 20 pages of people saying "yes, they look different, but if you obscure the surrounding image you see they are the same" with Ian responding "you rule8 idiot, they are the same color, I don't need to bother to obscure anything, I can see they are the same. Everyone around me is stupid". Typical bluster.

[Meffy]

:-D Seems a long way to go to reach "Well, they look different to me."

Did he have a take on illusions such as "Magic Zoomster" at the URL below -- do the segmented rings really rotate just because they seem to rotate? In this illusion there's no color perception to muddy the waters. I suspect this could even be built of solid materials. Would the perception of motion cause glued-down blocks of wood to shift?

Worse still, what if two people look at the screen together, one holding her head still while the other moves his head to and fro. She sees no rotation, he sees them whirling 'round, full o' fire. Whose reality prevails? Are the rings "really" moving or not? Is reality relative at this level? Has Will Rogers ever Metamind he didn't like? =O.o=

http://www.skytopia.com/project/illusion/illusion.html (about halfway down)

[Paul C. Anagnostopoulos]

Would the perception of motion cause glued-down blocks of wood to shift?
Motion is in the beholder, not in the "external object," just like with color.


Whose reality prevails?
The Metamind plays two different "realities" on the senses of the two beholders.

I have no idea. I'm just trying to grok Ian's metaphysic. If only I knew whether the senses are self or not-self.

~~ Paul

[Meffy]

Golly.

Ohhhhh... kay. :-} Thank you.

P.S.: Now I wonder whether the Metamind plays knick-knacks on my knee. But that's enough digression, for which again I must apologize.

[Mercutio]

Hmph. The dragon illusion won't print for me. Just a small segment of it.

hmph.

[Cabbage]

This link has jpegs of the dragon in three different colors; maybe this will print out for you:

http://www.pontomidia.com.br/ricardo/greatweb/gathering_for_gardner_paper_dragon.html

[Mercutio]

Cool! Thanks, Cabbage! Can't try it right now, but those look great!

[Angus McPresley]

This has been my favorite for a long time:

http://dogfeathers.com/java/spirals.html


For a fun time, look at the rotating spiral for 30 seconds, and then look at your palm.

Who needs drugs?

[Walter Wayne]

http://www.weizmann.ac.il/home/masagi/MIB/mib.html

Motion induced blindness, read the intructions and see the basic affect link. Other .gifs I've seen of this had a center dot to fixate on in order to help focus attention.

Basically, focusing near the center of the picture and watching the motion without moving your eyes, will cause the stationary dots to disappear once and a while.

I find this one interesting, since it doesn't deal with using perspective, or doing a trick of interpreting colour based on shadow and the like. It appears that eventually your brain decides the stationary dots are usless info, and the covers them over.

Perhaps that is how we deal with new blindspots in the middle of our field of view. Just interpret over them, like it does with you permanent blindspots. Sure there is a paper on it somewhere since motion induced blindness brings up many hits on google.

[CFLarsen]

Hmph. The dragon illusion won't print for me. Just a small segment of it.

hmph.
It's an illusion. Whaddaya expect?

[Gromit]

Both centre crosses in these objects are the same colour.
In honesty, JPG artifacting probably makes them slightly different, but I can at least say they are FAR similar than they appear in the image.

[Starthinker]

Pretty good, reminds me of the reverse-color US flag projection trick. :-)

Here's the most jawdropping animated GIF I've ever seen.

http://vygotsky.sfasu.edu/Courses/psy133/rotate_circles.jpg

The amazing part is that it's not animated. Let your gaze wander around the pattern and see the "snakes" slowly turn while not moving at all. I can't resist seeing motion even while knowing perfectly well that it's static. Can you?

[edit] Here's the parent page: http://vygotsky.sfasu.edu/Courses/psy133/illusions.html

I drive a VW Beetle (the old kind) and tried various ways to paint this on my car to get the illusion from a few car lengths away but it's not transferring well to actual paint on a larger scale. It will be cool when I get it right, though.

[American]

To me the castle feels just like when I'm not sure whether I'm dreaming or awake (I mean when you move the mouse and it looks like color).

I keep having more realistic dreams all the time. I fear when I get old and senile, I will truly be unable to distinguish my waking hours from sleeping dreams.

[Bradk3]

Both centre crosses in these objects are the same colour.
In honesty, JPG artifacting probably makes them slightly different, but I can at least say they are FAR similar than they appear in the image.

Okay, that one's as good as the checkerboard illusion! I had to open the picture up in MS Paint to verify that they are the same.

It's true!

[Rat]

Here's an interesting site on color perception. (Requires Java)
Color perception link (http://www.tsi.enst.fr/%7Ebrettel/DaltonDemo/DD08.html)

Normal sighted people are always surprised that the "Normal" and "Deutan" views are virtually identical to me, except perhaps for some shifts in contrast.
It's nice to see those splatter images (the ones that normally test for colour-blindness) in single-channel colour, just so I can see what it is that others are seeing. I still can't pick it out once I go back to full colour, but I guess that's kind of the point.

Cheers,
Rat.

[Mr. Scott]

Both centre crosses in these objects are the same colour.
In honesty, JPG artifacting probably makes them slightly different, but I can at least say they are FAR similar than they appear in the image.

That illusion is portrayed on a web site with other color illusions (http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html) that I shared with Renee Rynn a while back to try and convince her that colors didn't have the properties she believed they had.

All optical illusions make the same point: don't trust your perceptions.

I published an article on color reproduction that was actually used in high school science classes. It seems like we get stuck on semantic aguments -- are we talking about what colors are in the world or how colors appear to observers?

I made the point in my article:

There really is no such physical thing as "color." Color is an illusion our minds create when our eyes pick up various combinations of wavelengths of light in various contexts (the optical illusions demonstrate this).

A good example is the color yellow. An object in nature can look yellow if it actually reflects one wavelength of light that we see as yellow.

However...

...an object in nature can reflect the wavelength of red AND the wavelength of green and NONE of the wavelengths of yellow, and we will still see yellow.

Therefore...

...the color seen as "yellow" is an illusion, since we will see yellow when there is no yellow light at all. Look closely through a magnifier at a yellow area of a video screen, and you will see no yellow at all -- only red and green areas.

The castle illusion also demonstrates this. Here's its biophysics:

Brightly lit scenes are picked up by the "cones" in our retinas. We have three types: red, green, and blue. If we stare unmoving at a scene, the various colors exhaust the particular cones that are picking up the colors and transmitting their signals to the brain. When the image changes, the un-exhausted cones dominate and the exhausted ones fail to register their assigned colors until they recover their sensitivity.

For example...

...in the castle photo the original blue sky is represented in the chroma isolated negative as yellow -- more specifically the red and green wavelengths from your computer monitor. By staring at the picture without moving the eyes, the red and green cones of your eyes become exhausted but the blue cones become more sensitive from being unstimulated. When the cursor moves over the picture, the B&W representation appears. Keep in mind that the B&W picture on your computer monitor is actually not quite B&W but rather the sum of red, green, and blue light specifically (no yellow light). Now the blue cones in your eyes see the gray sky, but having become extra sensitive from a few seconds of deprivation, send a strong blue signal to the brain. The red and green cones, desensitized, fail to pick up much of their colors. The result is the gray looks blue -- the opposite color of the first image.

So that we don't get lost in a semantic argument, may I suggest that we be specific about the difference between the colors in the physical world (wavelengths of light in combination), and the colors in our perception? It seems that would keep away the goofy Uninteresting Ian interpretations.

[Dogdoctor]

The illusion works well for me but not at all for my wife for some reason.

[Mercutio]

[snip]The castle illusion also demonstrates this. Here's its biophysics:

Brightly lit scenes are picked up by the "cones" in our retinas. We have three types: red, green, and blue.
[snip]
If you had posted something wildly inaccurate, I'd have let this go. But as it is, your post was very good, so I have to correct you on this.

Color Vision researchers (I count at least 3 among my friends) absolutely loathe it when people refer to the cones as "red, green, and blue". This chart (http://www.ryobi-sol.co.jp/visolve/en/figs/coneFund.png) has them labeled L, M, and S (for long, medium, and short), but even that is misleading, considering the overlap--especially between the L and M pigments. The purists in our department refer to them as the alpha, beta, and gamma photopigments, which does not tempt one to think of them as "absorbing light of X color".

Note that the "red" cones are maximally sensitive to a slightly greenish yellow, but respond to light along the entire continuum of the visual spectrum. The relative combinations of the bleaching photopigments are what are interpreted (through the opponent-process system) as color, as you say.

Oh...and it is not our "minds" which create the illusion of color. But that debate will have to wait...

[Bodhi Dharma Zen]

It takes a great deal of effort to understand Ian, but I find it quite worth it.

I have been out of the forum for a while... but this is outrageous. Difficult to understand????? in which world? His thinking is transparent, and very obvious. Of course I would not take this out of context, but reading your last posts seems that you agree with him?? so... there are immaterial souls that survive the body?

Please tell me that you just find the interpretations (Ian btw just reads them and believe in them because they appear to let his souls survive, but such interpretations are not product of his mind) appealing, and that you dont buy all his paraphernalia.

[Mercutio]

I have been out of the forum for a while... but this is outrageous. Difficult to understand????? in which world? His thinking is transparent, and very obvious. Of course I would not take this out of context, but reading your last posts seems that you agree with him?? so... there are immaterial souls that survive the body?

Please tell me that you just find the interpretations (Ian btw just reads them and believe in them because they appear to let his souls survive, but such interpretations are not product of his mind) appealing, and that you dont buy all his paraphernalia.
BDZ, I do not dismiss what Ian says about science and perception simply because I disagree with him about survival of consciousness.

In my opinion, Ian is quite wrong about some things. In my opinion, many people (perhaps including yourself) dismiss what he says simply because it is Ian saying it, and not on the merits of what he says. There have been several threads here where Ian has said something perfectly defendable, following which he was bombarded by people who wished to practice "illogic by association".

Ian says X. X is quite clearly wrong. People go nuts pointing this out.
Ian says Y. Y is independent of X. People go nuts complaining about X.
Ian gets mad at people complaining about X when he said Y. People go nuts complaining about Ian getting mad.

I am speaking of the Y topics here. It matters not a whit to me whether the X topics comprise 10% or 90% of what Ian says.

It makes life much easier to pretend that all Ian posts are X. It allows us to dismiss him without effort or thought. In truth, though, some Ian posts are Y, and are worthwhile.

In passing, I also find it helps to try not to engage in speculation about Ian's motivation. You say you have already decided why he posts X and Y, and what he believes. Be careful; such attributions allow you to see Y as X. When you complain about an Ian you have defined for yourself, you shouldn't be surprised when A) he acts like you expect him to, while B) claiming he is not.

[Paul C. Anagnostopoulos]

This chart has them labeled L, M, and S (for long, medium, and short), but even that is misleading, considering the overlap--especially between the L and M pigments.
Thanks for that chart, Merc. I did not realize there is so much overlap in sensitivity.

~~ Paul

[Paul C. Anagnostopoulos]

Ian says X. X is quite clearly wrong. People go nuts pointing this out.
Ian says Y. Y is independent of X. People go nuts complaining about X.
Ian gets mad at people complaining about X when he said Y. People go nuts complaining about Ian getting mad.
Part of the problem, just as one would expect, is that Ian also does this. He's pounding strawmen materialisms all the time.

We spend a lot of time comparing incomplete -isms here. People put forth half-baked proposals for idealism, materialism, neutral monism, etc. that do not explain everything we see in the world. Then we argue which proposal is better. Sometimes we even invoke Occam. But the proposals do not explain everything, so there is really no point in comparing them. Some examples:

idealism: Why does the world appear consistent to all minds (and how would you test your conjecture)?

neutral monism: What is this 1 + -1 = 0 thing, anyway (and how would you test the math)?

materialism: (okay, I'm working hard here ... come on ...) How can the feeling of subjective experience arise from brain processes?

I suggest that when all the details are worked out, these -isms will be identical. After all, they are explaining the same world.

~~ Paul

[tsg]

BDZ, I do not dismiss what Ian says about science and perception simply because I disagree with him about survival of consciousness.

In my opinion, Ian is quite wrong about some things. In my opinion, many people (perhaps including yourself) dismiss what he says simply because it is Ian saying it, and not on the merits of what he says. There have been several threads here where Ian has said something perfectly defendable, following which he was bombarded by people who wished to practice "illogic by association".

Ian says X. X is quite clearly wrong. People go nuts pointing this out.
Ian says Y. Y is independent of X. People go nuts complaining about X.
Ian gets mad at people complaining about X when he said Y. People go nuts complaining about Ian getting mad.

I am speaking of the Y topics here. It matters not a whit to me whether the X topics comprise 10% or 90% of what Ian says.

It makes life much easier to pretend that all Ian posts are X. It allows us to dismiss him without effort or thought. In truth, though, some Ian posts are Y, and are worthwhile.

In passing, I also find it helps to try not to engage in speculation about Ian's motivation. You say you have already decided why he posts X and Y, and what he believes. Be careful; such attributions allow you to see Y as X. When you complain about an Ian you have defined for yourself, you shouldn't be surprised when A) he acts like you expect him to, while B) claiming he is not.

Ian brings this on himself. I can't take anything he says seriously because of his arguments where he makes completely ridiculous claims, refuses to support them, and then calls whoever doesn't just take his word for it "stupid skeptics". I don't have the time or the desire to dig through all the horsecrap to find the gem. Is this a case of poisoning the well? Sure, but it's Ian who poisoned it. Act like an ass and you'll get treated like an ass, even if you happen to be right.

[Mr. Scott]

Color Vision researchers (I count at least 3 among my friends) absolutely loathe it when people refer to the cones as "red, green, and blue".

Thanks for being generally complimentary and correcting me on a fine point. What if I defined the red cone as the cone type which, when stimulated alone while the other two types are not stimulated, produce the sensation of light primary red? Would that be accurate even though momentarily neglecting the overlap and the exact graph of sensitivity of the "L" cone's pigment? Ditto for the other two.

The overlap is of course essential to seeing the full rainbow of colors. Otherwise, a pure yellow light would look black if it fell between non-overlapping long and medium receptors.

Oh...and it is not our "minds" which create the illusion of color. But that debate will have to wait...

Minds -- brains -- a semantic disagreement? When you close your eyes and press them with your fingers and see bright colors, what object is emitting or reflecting those colors? Or if we dream in color, what wavelengths of light are reaching our eyes? The sensation of color is created by the brain. The physics of color is just about wavelengths of light which may or may not correlate to perception, as the castle illusion amply demonstrates.

One more -- what color is my car if illuminated at night by sodium vapor street lamps and it looks white even though it is red in the daylight -- so different in appearance that I can't recognize my own car? Is that white color in the physical world? Or only in my mind?

[Mr. Scott]

Normal sighted people are always surprised that the "Normal" and "Deutan" views are virtually identical to me, except perhaps for some shifts in contrast.

I had a friend who was red/green color blind and I was able to study his affliction until it made him too upset. He had a number of delusions which may have been hallucinations he'd developed to adapt to living with full-sighted people:

1) If he saw a red or green object with no context to give him clues, like a red neon light, he described it as a "nondescript color." I'd never call any color "nondescript," but that was the word he used to describe red or green out of context.

2) He could see in a color photograph that a red flower was against green leaves, but if I cut a hole in a card and showed him only a leaf part or only a flower part, he couldn't tell which was which. The "redness" he perceived in the flower and the "greenness" he perceived (hallucinated) in the leaves vanished. This was the test that really injured his ego.

3) He believed he could see colors on black and white television. He might say "wow, what a bright red dress she is wearing" and full sighted people say, "What? Huh?" He couldn't understand why others couldn't see the colors he thought he could see in B&W pictures.

I was asked if, when he thought someone was wearing a red dress on B&W television, the dress really was red and he had perceptive skills above and beyond us with normal vision. A woo hypothesis.

[Mr. Scott]

The illusion works well for me but not at all for my wife for some reason.

She undoubtedly doesn't have enough eyeball control to keep her focus stationary for long. Can she see the hidden pictures in stereograms?

[Grundar]

It's nice to see those splatter images (the ones that normally test for colour-blindness) in single-channel colour, just so I can see what it is that others are seeing. I still can't pick it out once I go back to full colour, but I guess that's kind of the point.

Cheers,
Rat.

That was what i really enjoyed about that link too. Nice to know I'm not the only one.

/Hans

[Bodhi Dharma Zen]

some Ian posts are Y, and are worthwhile.

Well, of course. But this is not the point, you react against those who trash everything Ian says just because he is the one saying it, but at the same time it appears that you believe his thinking is correct. It is not. If he utters some coherent things its because he has read some arguments and hand picked them when they appear to support his claims.

And his claims are simply wrong, and are illogical.

So, if he uses certain argument to support them, one cannot see the argument as an isolated event, its part of his thinking, and because of that, even if the argument is not wrong per se, is still wrongly used.

I hope you can see my point. It is not my interest to "bash Ian" but to correctly see his arguments in context of his thinking.

[Bodhi Dharma Zen]

We spend a lot of time comparing incomplete -isms here. People put forth half-baked proposals for idealism, materialism, neutral monism, etc. that do not explain everything we see in the world. Then we argue which proposal is better. Sometimes we even invoke Occam. But the proposals do not explain everything, so there is really no point in comparing them.

Cant agree more. Most of the discussions in here are absurd in that sense. Still, they are fun, and one can learn from them. Those are the only reasons we have (I think) to participate. We are not solving anything.

[Mercutio]

Well, of course. But this is not the point, you react against those who trash everything Ian says just because he is the one saying it, but at the same time it appears that you believe his thinking is correct. It is not. If he utters some coherent things its because he has read some arguments and hand picked them when they appear to support his claims.
Um...I have argued against Ian at length about some things. I don't know how you can think that I accept everything he says. Within my first week here, Ian called something I said ... a name I can't repeat.

I do not agree with you that he only believes the things he does in order to justify this one uber-belief. (And you know, from reading my arguments against Iacchus, that I am not opposed to saying that this is the case when I believe that it is.)

[Bodhi Dharma Zen]

I see. One thing is true, and I have to recon it. You are capable of separating the person from his arguments. Well done. I think I do get carried away with the person sometimes, specially when they start to talk with their guts and not their brains.

Kudos for that!

[Mercutio]

Thanks for being generally complimentary and correcting me on a fine point. What if I defined the red cone as the cone type which, when stimulated alone while the other two types are not stimulated, produce the sensation of light primary red? Would that be accurate even though momentarily neglecting the overlap and the exact graph of sensitivity of the "L" cone's pigment? Ditto for the other two.
Well...I'd probably politely suggest you should have stopped while you were ahead. It doesn't work that way. Hurvich & Jameson found the connection between the trichromatic signals at the retinal layer and the opponent processing signals, as illustrated here. (http://www.physics.utoledo.edu/~lsa/_color/24_rchan.gif) It is a combination of excitatory and inhibitory signalling from the cones that gives rise to a system that initially seemed wholly incompatible with trichromacy (seriously, red-green, yellow-blue, and black-white opponent process systems, coming from 3 overlapping pigments?)

As for the "cone type that produces a primary red", note that red is an interesting case, seeing as there is "redness" on both ends of the spectrum, on the violet end as well as the red end. (http://www.physics.utoledo.edu/~lsa/_color/24_hueCancel.jpg) Unless I am mistaken (quite possible, actually), there actually is no single wavelength that is perceived as "unique red" (red without any blue or yellow in it), and we must mix wavelengths in order to produce a "pure" red. (In contrast, there are single wavelengths for unique yellow, green, and blue.)

The overlap is of course essential to seeing the full rainbow of colors. Otherwise, a pure yellow light would look black if it fell between non-overlapping long and medium receptors.
More complex, again. If we only had 2 photopigments, we would be able to match any perceived color with only two lights (at appropriate intensities), and any place where the ratios were about the same (vast areas under our overlapping pigments) would be impossible to discriminate among. As is, our trichromatic vision can be fooled, as your computer or televisions demonstrate quite well, with only three lights. (There is some evidence of quadrachromats, for whom televisions and computer monitors do not look like accurate pictures of the real world.)

Minds -- brains -- a semantic disagreement? When you close your eyes and press them with your fingers and see bright colors, what object is emitting or reflecting those colors? Or if we dream in color, what wavelengths of light are reaching our eyes? The sensation of color is created by the brain. The physics of color is just about wavelengths of light which may or may not correlate to perception, as the castle illusion amply demonstrates.
The doctrine of Specific Nerve Energies (Muller) recognizes that stimulation of any sort of a visual nerve will result in visual sensation; any auditory nerve stimulation in auditory sensation, etc. It matters not what the stimulation is--light, pressure, whatever. When the visual cortex is stimulated (whether by light in the retina, or through brainstem activity, or through classical conditioning), what would you expect it to do besides "see"? When we dream, there is no wavelength reaching our retina; no explanation of vision would suggest it, so it is no surprise and no argument against any physical interpretation.

One more -- what color is my car if illuminated at night by sodium vapor street lamps and it looks white even though it is red in the daylight -- so different in appearance that I can't recognize my own car? Is that white color in the physical world? Or only in my mind?Color constancy is among the topics vision researchers have studied for decades. Receptive fields (with excitatory/inhibitory center/surround fields) are part of the explanation, but not the whole. My favorite (partial) explanation is simply that what we think happens does not happen; that is, our visual perception is nowhere near as accurate or as sensitive (or as constant) as we believe it is. "Change blindness" experiments are a stunning demonstration of this.

[sadluxation]

Who's ian?

My Beever's more impressive.

http://forums.randi.org/imagehost/9184498603321b4e.jpg

[Bodhi Dharma Zen]

The doctrine of Specific Nerve Energies (Muller) recognizes that stimulation of any sort of a visual nerve will result in visual sensation; any auditory nerve stimulation in auditory sensation, etc. It matters not what the stimulation is--light, pressure, whatever...

... My favorite (partial) explanation is simply that what we think happens does not happen; that is, our visual perception is nowhere near as accurate or as sensitive (or as constant) as we believe it is. "Change blindness" experiments are a stunning demonstration of this.

To me its even more interesting to realize that sometimes, even when the cognition happens, the individual doesn't experience anything. "Innatentional Blindness" by Mack & Rock depict such instances.

[This Guy]

To me its even more interesting to realize that sometimes, even when the cognition happens, the individual doesn't experience anything. "Innatentional Blindness" by Mack & Rock depict such instances.

I think there is a similar effect that relates to the hearing on the part of teenagers ;)

[Meffy]

I think there is a similar effect that relates to the hearing on the part of teenagers ;)
Part of it is religious. See http://forums.randi.org/showthread.php?p=1706471#post1706471

[This Guy]

Part of it is religious. See http://forums.randi.org/showthread.php?p=1706471#post1706471

LOL

[Mercutio]

To me its even more interesting to realize that sometimes, even when the cognition happens, the individual doesn't experience anything. "Innatentional Blindness" by Mack & Rock depict such instances.
Define "even when the cognition happens" and "experience". Separately. Tell me how you know the first occurred but the second did not.

Nah, it's not you...it's "cognition". There's a reason behaviorists don't use the term.

[Mr. Scott]

Well...I'd probably politely suggest you should have stopped while you were ahead.

I'll politely point out that was an obnoxious remark for a moderator to make.

My description was sufficiently simplified to explain the principle of the castle illusion to newcomers to color theory.

Hurvich & Jameson found the connection between the trichromatic signals at the retinal layer and the opponent processing signals, as illustrated here. It is a combination of excitatory and inhibitory signalling from the cones that gives rise to a system that initially seemed wholly incompatible with trichromacy (seriously, red-green, yellow-blue, and black-white opponent process systems, coming from 3 overlapping pigments?)

Yes, I know all about that, but it's irrelevant to the castle illusion. Most people don't even understand the additive color system, so it wasn't a good idea to burden them with such irrelevancies.

Now that this debate has become more about egos than about vision and optical illusions, I'm bailing.

[Mercutio]

I'll politely point out that was an obnoxious remark for a moderator to make.
It was not made as a moderator. We are human beings, you know. When we speak as moderators, we have little boxy deallies that emphasize that.

eta: my comment was intended as a humorous, direct answer to your "what if" question. Nothing more.

My description was sufficiently simplified to explain the principle of the castle illusion to newcomers to color theory.
I agree completely. As I said, I would not have said anything at all if you had not posted such an excellent explanation in the first place. I had hoped that comment would have alerted any newcomers that the following discussion was hairsplitting.
Yes, I know all about that, but it's irrelevant to the castle illusion. Most people don't even understand the additive color system, so it wasn't a good idea to burden them with such irrelevancies.
Again, you are quite right. My post was not addressed to "most people", but to someone who had demonstrated superior understanding. I could not know whether you knew even more, but were condensing for understanding, or whether your post reflected a misunderstanding of your own. Again, it was addressed specifically to one who had already demonstrated understanding. And the followup was an answer to the specific question you asked: "what if I defined...." At that point, it was no longer a general-knowledge question.

Now that this debate has become more about egos than about vision and optical illusions, I'm bailing.I am very sorry if you think this is about egos. I do not agree; it is about details. Neither of us can know anything more about what the other posts than what we post. I address what you have written, nothing more. Feel free to correct my own misstatements; I look forward to it.

I agree, it is tricky to walk the line between explanation and oversimplification; I think you did an excellent job. If you are offended that I took it a step further, I am very sorry. We do have people here who are, in my opinion, quite ready for that next step; I do not intend to invalidate what you have said, but rather to expand on it. If something in how I said it was what offended you, I again apologize. Even better, if you can take what I said and show how it can be improved upon, I welcome it.

[Mr. Scott]

eta: my comment was intended as a humorous, direct answer to your "what if" question.
If I fell victim to the Internet Effect of misreading emotional content in a posting because it's merely ASCII text, then I apologize.
it is tricky to walk the line between explanation and oversimplification; I think you did an excellent job.
Again appreciate the compliment. Perhaps I should start such a posting with something like: "the following is a simplification intended to clarify the principles for the newcomer to the subject."

Back to colors...

What's responsible for the sensation of yellowness in the mind if that sensation can be produced by pressing your eyes or dreaming of yellow, or looking at a gray spot surrounded by a scene apparently lit by blueish light, like the crosses illusion (http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html)? Certainly not the wavelength of yellow light. Isn't color therefore a non-Ian-style figment of the mind/brain/whatever?

[tkingdoll]

As an aside, Mr Scott, I was extremely grateful for your post, as I had been looking for an explanation for the effect and yours was perfect (by which I mean, I understood it all). Thanks.

[Bodhi Dharma Zen]

Define "even when the cognition happens" and "experience". Separately. Tell me how you know the first occurred but the second did not.

Nah, it's not you...it's "cognition". There's a reason behaviorists don't use the term.

Yes. Im aware of that. In fact, I believe the confusion comes from the still predominant dualist point of view, even when it is just implicit and not explicit. Our very language is, somehow, designed to create this dualist approach.

Maybe it would be better to say that there are unattended experiences, because the subjective focus of attention lies elsewhere. Bah, words are sometimes more an obstacle than a tool.

[Mr. Scott]

As an aside, Mr Scott, I was extremely grateful for your post, as I had been looking for an explanation for the effect and yours was perfect (by which I mean, I understood it all). Thanks.

tkingdoll, if I could jump into my computer screen, ride the fiber optic cable under the Atlantic to the UK, jump out of your computer screen and give you a warm hug, I'd demonstrate it to Randi and win the million.

The Castle Illusion is a fascinating new (to me) application of the well-known afterimage effect. I created the example below for you based on the one I'd known all my life. Stare at the black dot in the middle of the flag without moving your eyes for about 20 seconds, then look at a blank white surface again holding your eyes still, and you'll see the flag in correct color. In the Castle Illusion, the chrominance picture on your retina's afterimage is added to the luminance (B&W) picture on your computer screen and the brain gets the sum -- a full color picture.

http://forums.randi.org/imagehost/67364499485d260b2.jpg

[Mercutio]

Back to colors...

What's responsible for the sensation of yellowness in the mind if that sensation can be produced by pressing your eyes or dreaming of yellow, or looking at a gray spot surrounded by a scene apparently lit by blueish light, like the crosses illusion (http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html)? Certainly not the wavelength of yellow light.I have two separate responses to this--first, the "yellowness of the mind" phrasing of the question presupposes a dualistic view that, in my opinion, is not helpful in exploring the question. It is not your fault, of course; it is the way our language community has spoken about perception since, oh, Descartes, or maybe even Plato. I see, on the table near me, a yellow banana. I do not perceive a sensation of yellowness, I see a yellow thing. Exploring how it is that we see things is liable to be much more useful than exploring how a "sensation of yellowness" arises in one's mind. (This comment is not directed mainly at you--I have had more than a few conversations, here and elsewhere, in which a thorough explanation of the visual system as we currently understand it is derailed by "but what gives rise to the sensation?", as if it were somehow separate from the process of seeing a given object. It is the assumption of dualism that gives rise to that question, and it is purely an assumption, not anything founded in experience.)

The second thing...What is responsible? In both cases, there is a clear physical stimulus. In the first, a physical pressure; in the second, a complex visual stimulus. In neither case is there reason to suspect that an explanation requires more than examination of the retinal and cortical visual pathways. In the first case, there is essentially a counterfeit stimulus--you are seeing yellow (or red, or blue, or whatever) because the nerves stimulated by pressure are the ones that feed into the yellow-blue opponent process system. The second...which is a great illusion... is an example of an area of exploration which has seen quite a bit of theory and experiment. Land's "retinex" theory (utilizing "mondrian" stimuli to explore different phenomena) proposed an interaction (which he described in mathematical terms) between the color receptors of the eye, dependent on not just a given center color, but all the colors surrounding it, and the light that is illuminating the scene. Land thought that all the processing took place at the retinal level; we no longer think this.

To the best of my knowledge (I will ask my color-vision researcher friends, though), the best current explanations have to do with receptor fields, and the excitatory/inhibitory signals sent to the opponent process channels via these fields. The same process which, in the monochromatic black/white channel, is responsible for the Hermann Grid illusion (here's one) (http://dragon.uml.edu/psych/hgrid.html) and Mach Bands, may be responsible for center/surround color illusions.
Isn't color therefore a non-Ian-style figment of the mind/brain/whatever?I don't see why. Besides which, what sort of an explanation is this? "It is something the mind does." Ok...how? We have the same problem we had before, but now we call it a "figment of the mind" and treat it as if it was no longer a function of the visual pathways. This isn't science, it is giving up.

[Mr. Scott]

"It is something the mind does." Ok...how? We have the same problem we had before, but now we call it a "figment of the mind" and treat it as if it was no longer a function of the visual pathways. This isn't science, it is giving up.

Well, I've been asking this question for decades and no one has been able to supply an answer. I'd hardly call that giving up. Sure, I'd like to know how the mind produces the sensation of color. Since I can experience that sensation in a dream, it obviously has nothing to do with wavelengths of light or the neural networks of the retina. I still remember asking my dad this question when I was just eleven years old (a very long time ago). Being a PhD., he had the affliction of not being able to say "I don't know" and talked in circles (see Randi's Princeton lecture (http://video.google.com/videoplay?docid=4665376168764022836&q=randi) for this reference).

How does the mind produce sensations? I don't know, but I'd like to some day. For now, it's in the box of questions that also holds "What was there before the big bang?"

[Bodhi Dharma Zen]

At some point, all the arguments regarding this become circular. Interesting... isnt it?

[Bronze Dog]

At some point, all the arguments regarding this become circular. Interesting... isnt it?
Godel would love to tell you all about that.

[Mercutio]

Well, I've been asking this question for decades and no one has been able to supply an answer. I'd hardly call that giving up. Given the progress over the past century in understanding visual perception, I am tempted to suggest that it is the question, or perhaps the tacit assumptions inherent in the question as phrased, that stands in the way.
Sure, I'd like to know how the mind produces the sensation of color. I'd like to know the location of the fountain of youth. Both of us are assuming something exists, and are asking about it, before allowing the evidence to guide what the real questions should be.
Since I can experience that sensation in a dream, it obviously has nothing to do with wavelengths of light or the neural networks of the retina. Your conclusion does not follow from your premise. One suggested explanation for visual experiences is Classical Conditioning; by that explanation, your dreams are visual because you have had plenty of experience with waking visual stimuli. This clearly has something to do with light and retinal stimulation. With the exception of the metaphorical usage of "vision", congenitally blind individuals do not experience visual imagery in dreams, and only rarely do individuals who have lost sight by the age of five. One study. (there are more) (http://psych.ucsc.edu/dreams/Library/hurovitz_1999a.html)
I still remember asking my dad this question when I was just eleven years old (a very long time ago). Being a PhD., he had the affliction of not being able to say "I don't know" and talked in circles (see Randi's Princeton lecture (http://video.google.com/videoplay?docid=4665376168764022836&q=randi) for this reference).
What is his Ph.D. in? Was it an appropriate area to address the question? (For the record, my students are shocked that I am perfectly willing to say "I don't know". Usually, though, that is followed by "let's see if there is anyone who does know!", a literature search, and the humbling discovery that there is a huge literature in an area of my own total ignorance.)

How does the mind produce sensations?And what does it mean to ask that? Is it the right question to ask?
I don't know, but I'd like to some day. For now, it's in the box of questions that also holds "What was there before the big bang?"
If you mean "unanswerable", I would agree. In both questions, the question itself assumes things that are not immediately obvious as assumptions, and which shape our expectations as to what an appropriate answer must be. Our implicit assumptions can act as blinders, keeping us from seeing answers that are perfectly adequate, but not in line with our preconceived notions.

[69dodge]

Your conclusion does not follow from your premise. One suggested explanation for visual experiences is Classical Conditioning; by that explanation, your dreams are visual because you have had plenty of experience with waking visual stimuli. This clearly has something to do with light and retinal stimulation.Aren't you taking the phrase "has something to do with" too literally? I assume Mr. Scott meant that, at the time he's dreaming, no light is stimulating his retina.

[Mr. Scott]

I'd like to know the location of the fountain of youth. Both of us are assuming something exists, and are asking about it, before allowing the evidence to guide what the real questions should be..

I know the sensation of color exists because I experience it. This has at times led me to wonder if those who deny sensation are not experiencing what I am experiencing.

If you mean "unanswerable", I would agree. In both questions, the question itself assumes things that are not immediately obvious as assumptions, and which shape our expectations as to what an appropriate answer must be. Our implicit assumptions can act as blinders, keeping us from seeing answers that are perfectly adequate, but not in line with our preconceived notions.

You refer to implicit assumptions without specifying them. As long as they defy specification, I'll assume their aren't any (Occam) ;) .

It's nice to know about wavelengths of light and pre-processing in the retina and the visual cortex, but I'd really like to know what's happening between there and the anterior cingulate (Penrose's choice) or whatever really is the seat of consciousness.

Here's an interesting take on what to me is a related issue: Conversations with Zombies (http://www.imprint.co.uk/Moody_zombies.html) by Todd C. Moody, from The Journal of Consciousness Studies. Are deniers of sensations and consciousness zombies themsleves? My own father -- a Zombie???? :D I only ask.

[Mr. Scott]

I assume Mr. Scott meant that, at the time he's dreaming, no light is stimulating his retina.

Exactly.

I stand by my assertion that colors are in the mind/brain and not in wavelengths of light, because the same wavelength can trigger any number of perceived colors. Even no-wavelength, photon-free color sensations (dreams, synesthesia).

IIRC, the right kind of stimulation to the brains of born-blind people will indeed cause photon-free sensations of color they have not had previously.

[Mercutio]

Aren't you taking the phrase "has something to do with" too literally? I assume Mr. Scott meant that, at the time he's dreaming, no light is stimulating his retina.
But of course no current theory of vision makes the requirement that light be stimulating your retina currently in order for you to have a visual sensation. As I mentioned, simple classical conditioning is sufficient to give rise to visual sensation with eyes closed or in complete darkness (as is physical pressure on the eye, as is brainstem-initiated cortical nerve activity). The simple fact of "no light on retina" is only a very small part of the picture.

The key is (and thus, the "has something to do with"), these sorts of visual sensations do appear to be dependent on prior visual stimulation of the "light on retina" sort. Kerr & Domhoff (2004, Dreaming) review and critique 40 years of research, confirming that congenitally blind individuals (and the vast majority of those blinded by age 5) have no visual imagery in their dreams.

(more in next post)

[Mercutio]

Exactly.

I stand by my assertion that colors are in the mind/brain and not in wavelengths of light, because the same wavelength can trigger any number of perceived colors. Even no-wavelength, photon-free color sensations (dreams, synesthesia).
Your examples are incomplete. The same wavelength can trigger many perceived colors, certainly; this is not nearly as remarkable when you recall that even retinal processing (let alone cortical) of light stimulation at a given point is dependent on the light hitting other points. Again, the center/surround perceptual fields demonstrated by Hubel & Wiesel show one way by which this is accomplished.

And my claim is not that "colors are in wavelengths of light". Rather, by understanding the visual apparatus and light stimuli, the phenomena of color vision are explained without the need for dualistic notions of mental "sensations" somehow being generated by mind or brain. The questions about "sensations" that treat them as somehow separate from the process, are asking questions which presuppose a particular type of answer. When a complete answer does not fit that type, it is assumed to be incomplete.

IIRC, the right kind of stimulation to the brains of born-blind people will indeed cause photon-free sensations of color they have not had previously.I'd love to see a study on it. Raz, Amedi, & Zohary (2005, Cerebral Cortex) found that activation of occipital cortex (visual cortex in sighted people) of congenitally blind humans was associated with verbal memory. Neural plasticity doing what it does, the cortex not being used for vision was taken over by other tasks. (other papers suggest that there is some common processing of visual and tactile spatial relations, but I have found no evidence of color sensation in congenitally blind. (besides... how would they know? How would they know to label this thing they have never before experienced as "red"?)

[Mercutio]

I know the sensation of color exists because I experience it. This has at times led me to wonder if those who deny sensation are not experiencing what I am experiencing.
What is the difference between "seeing a red thing" and "experiencing the sensation of red when looking at a thing"? The language you use is consistent with the second, and includes reification of "sensation" as a (IMO, superfluous) step in the seeing of a thing. If you see no difference between the two phrases, then ...
You refer to implicit assumptions without specifying them. As long as they defy specification, I'll assume their aren't any (Occam) ;) .
...then those are the implicit assumptions you are unaware of. Any time we are using phrases like "gives rise to conscious experience" or "creates the experience of a color", we are adding an extra step. If we are asking for an explanation of that process before actually verifying that such a process occurs, we are looking for that fountain of youth I spoke of in my earlier post.

It's nice to know about wavelengths of light and pre-processing in the retina and the visual cortex, but I'd really like to know what's happening between there and the anterior cingulate (Penrose's choice) or whatever really is the seat of consciousness.
I don't know if you are using it this way, but too many others use this as a foot-in-the-door to a Cartesian Theatre. "Seat of consciousness" is another of those phrases that comes loaded with implicit assumptions of dualism.

Here's an interesting take on what to me is a related issue: Conversations with Zombies (http://www.imprint.co.uk/Moody_zombies.html) by Todd C. Moody, from The Journal of Consciousness Studies. Are deniers of sensations and consciousness zombies themsleves? My own father -- a Zombie???? :D I only ask.I'll take a look--thanks! (if you search this forum for Zombie, p-zombie, or m-zombie, you will see that there are many of us here who are perfectly comfortable with the possibility that we are zombies. Rather than "denying consciousness", one may turn the same thing on its head and say "refusing to make up something that is not there."

[alfaniner]

...

1) If he saw a red or green object with no context to give him clues, like a red neon light, he described it as a "nondescript color." I'd never call any color "nondescript," but that was the word he used to describe red or green out of context.


I can second that. Quite often I can see that there is a color "there", but can not give it a name, although I can name several colors that it is "not". Mostly the problem is with printed pastel colors, but little LED's (like on computers) give me a lot of trouble also. I once had trouble with computer support because they asked me what color the indicator lights were on the back. Most of the time they are either red, yellow, or green (never blue -- I can tell that!!) and look virtually identical, just bright.


2) He could see in a color photograph that a red flower was against green leaves, but if I cut a hole in a card and showed him only a leaf part or only a flower part, he couldn't tell which was which. The "redness" he perceived in the flower and the "greenness" he perceived (hallucinated) in the leaves vanished. This was the test that really injured his ego.


For me, context also plays an important part.


3) He believed he could see colors on black and white television. He might say "wow, what a bright red dress she is wearing" and full sighted people say, "What? Huh?" He couldn't understand why others couldn't see the colors he thought he could see in B&W pictures.


Sometimes I read a light gray as pink, even though I can rarely see true pink.

[Rat]

For me, context also plays an important part.I can't pick strawberries very well. If I look at one, I can see that it's red. And I can see that the leaves are green. But I can't very well see the strawberries among the leaves, so it's hard to say how much of my perception of the colours is down to context.

Cheers,
Rat.

[Mercutio]

A diagnosis of colorblindness is made based on specific tests. Many people who are technically colorblind are really "wide-field trichromats"--that is, they have some, but not the normal amount, of the third photopigment (or the spectral sensitivity curve of one pigment is shifted, as in anomalous trichromats like me), the upshot being that they can see color perfectly well in some situations, and not at all in others. I am most familiar with the studies on the effect of visual angle on this (larger stimuli may be perceived in proper color, but smaller ones not), but it may be that there are effects of brightness, or of surrounding color, I don't know. It is an interesting question, though.

[Niki]

These are awesome. I have always enjoyed optical illusions and these are wonderful!

[Touched]

I agree, very nice illusions posted here! It reminds me of trips to the Exploratorium in San Francisco -- so many hands-on experiments in human perception.

[Dark Jaguar]

I can't pick strawberries very well. If I look at one, I can see that it's red. And I can see that the leaves are green. But I can't very well see the strawberries among the leaves, so it's hard to say how much of my perception of the colours is down to context.

Cheers,
Rat.

Wow, that's totally alien to me. Are you sure you aren't seeing another shade of green or something and thinking that you are seeing a distinct other color? I have had the experience of seeing a lot of darker and lighter shades of green, or mostly green with some blue, and been able to distinguish each as a distinct color in the same way you would distinguish different shades of grey as their own color, but if suddenly a red thing is tossed in there, bam, that is far more distinctly a different color.

Blue and green seem somehow "closer" to each other than red is to either one though. I wonder if that's the normal look of them? I've never confused "true blue" with "true green" and those two do look distinct, just not AS distinct. Yellow, which I realize now is pretty much just an illusory color, seems far more of a completely distinct color from any of the others than blue and green do from each other. Yellow is like red in it's distinctness, though ligher shades are like THIS close to being plain ol' white.

At any rate, strawberries look completely different than the leaves they are intermingled with.

[Mr. Scott]

Rather than "denying consciousness", one may turn the same thing on its head and say "refusing to make up something that is not there."

Another hypothesis relates to our malady du jour Asperger's Syndrome. It's a mild form of Autism that makes many otherwise-brilliant people rather zombie-like. A famous Asperger's person is Temple Grandin, an author recently brought up in the "Do animals feel? (http://forums.randi.org/showthread.php?t=57095&highlight=animals)" thread. Could consciousness deniers, including those in the Artificial Intelligence field, be missing a good copy of a gene that endows us with conscious sensations? This would be like a color blind person saying people who see red and green are making something up that isn't there.

I have a friend who was once very close to an Asperger's sufferer who was brilliant but pretty much a zombie. So clever, in fact, that he learned how to fake emotions to get along with people, and could readily admit to faking them. They walk among us! :D (Could they pass the Turing Test?)

I can imagine how listening too closely to an Asperger sufferer's theories about consciousness could lead one astray.

[Mr. Scott]

I agree, very nice illusions posted here! It reminds me of trips to the Exploratorium in San Francisco -- so many hands-on experiments in human perception.

The optical Illusion Benham's Disk (http://www.michaelbach.de/ot/col_benham/index.html) should be mentioned here. You spin a wheel made up of nothing but Black and White markings, and colors appear. Interesting references there for articles on "subjective colors." I'd like to know if color blind people see colors in it they've never seen before.

[Mr. Scott]

I'd love to see a study on it [born-blind people seeing colors through direct brain stimulation]

I can't recall the actual study and that may be a false memory, but I'm pretty sure I learned that deaf people (maybe only young ones) could hear for the first time through direct cochlear nerve stimulation.

Then again, spontaneous atrophy being what it is, I'd not be suprised to learn that born-blind people, by adulthood, have had their visual systems rendered inoperative or reassigned and are therefore unrecoverable. I'll backpedal on that point.

[Rat]

...At any rate, strawberries look completely different than the leaves they are intermingled with.
Yes, they do to me as well, when I look at them individually. It's kind of impossible to explain, or, I guess, to imagine. Red and green (I am, of course, red/green colour-blind) look very different to me. I certainly perceive them as two separate and very different colours. But the strawberries just don't stand out for me.

I also perceive green as closer to blue. I don't know if there's a clue in your allusion to shades of grey. If, in good light and minimal shadows, you take a greyscale picture of a strawberry field, I suspect that the strawberries and the accompanying leaves would come out a similar shade of grey to each other. I further suspect that this would not be the case if the strawberries were yellow. And indeed, I can pick out unripe (yellow) strawberries with no problem. But when I've tried to explain it that way before, people come to the conclusion that I must see in black and white, which is patently not true.

And it can't be that I can tell the colour of each individually only because I know already what colour they are, because if you held up cards of red and green, I could get them right every time. If, however, you arranged the cards (assuming there were a lot of them) in a pattern so that the red cards made an image among the green ones, I would have difficulty picking that pattern out. This is a simplified version of how the splatter pattern tests work, of course.

On the other hand, I do have real difficulty telling green and brown apart. If you don't have blue eyes, I'm unlikely to be able to tell you what colour your eyes are. Unless you're albino. Truth be told, I don't know what colour my own eyes are, but I think I remember them as brown. Unless it's a very vivid green, or a very muddy brown, I think this is were I really do rely on knowing beforehand what colour something is. I know that wood is brown and (living) leaves are green. But if you're wearing an item of clothing (say, a t-shirt) that could be either, it's unlikely I could tell, again, unless it was were vivid-green/muddy-brown.

It makes for some interesting moments, but unless you have a career planned as a train driver or electrical engineer (both of which are barred to me), it's hardly an affliction. And I'm told it does have some advantages, which may explain why it continues to exist, in other apes as well as humans. There is a story (I don't know if it's true) that bomber crews used to like to take a colour blind crew member on board, because while they miss certain things, there are other things that they see rather vividly, and thus can pick out camouflaged targets. This may also apply to gathering fruit for apes. Certainly if I see gold against brown, the contrast is almost painful to me, with a shimmering line between the two, and I'm told that others (even some colour-blind people) don't get this effect, though I have heard it from some other colour-blind people.

Cheers,
Rat.

[Mercutio]

Yes, they do to me as well, when I look at them individually. It's kind of impossible to explain, or, I guess, to imagine. [big snip]
Cheers,
Rat.
If memory serves, a very very small number of people are congenitally colorblind in just one eye, with normal vision in the other. It is the testimony of people like this that gives researchers their picture of "what color-blindness looks like".

[Mercutio]

The optical Illusion Benham's Disk (http://www.michaelbach.de/ot/col_benham/index.html) should be mentioned here. You spin a wheel made up of nothing but Black and White markings, and colors appear. Interesting references there for articles on "subjective colors." I'd like to know if color blind people see colors in it they've never seen before.
What a great question! I would predict, based on a behavioral view of language learning, that color blind individuals would see the same colors they do in response to other stimuli. But it is a falsifiable prediction, which is the great thing about empiricism. It would be a simple test, too! We could do it with only the color-blind people who have posted to this thread, and a couple of print-out disks.

(Grunfeld & Spitzer (1995, Vision Research) take a look at Benham's Disk...from their abstract: "... a general spatiotemporal model for the subjective color phenomenon of Benham's disk based on general cell response to inhibitory stimulation and differences among 3 color pathways. The model takes into account known spatial and temporal properties of the color-coded ganglion cells, including specific nonlinearity (the rebound response) which is suggested to initiate the effect.")

[Mercutio]

I can't recall the actual study and that may be a false memory, but I'm pretty sure I learned that deaf people (maybe only young ones) could hear for the first time through direct cochlear nerve stimulation.
A quick and cursory EBSCOHOST search suggests that there are critical periods. Looks like after people have learned to recognise speech, they can lose hearing for decades (and have auditory cortex taken over by other processing) and still regain it (and retake that cortex. Very cool...), but if hearing is lost early, the longer the wait before a cochlear implant, the more difficult it is to gain hearing. Hearing loss at a younger age makes speech recognintion more difficult, although tone recognition may be possible.

Did not see anything about congenitally deaf with cochlear implants in adulthood. Kids, yes. Cats, yes. But it was a quick and cursory search.

[Jeff Corey]

If memory serves, a very very small number of people are congenitally colorblind in just one eye, with normal vision in the other. It is the testimony of people like this that gives researchers their picture of "what color-blindness looks like".
Memory serves and aces, Merc. John Dalton, 18th century English chemist first described this condition that he had. Red-green colorblindness(protanopia) is still called Daltonism, at least in French,

[Mercutio]

It makes for some interesting moments, but unless you have a career planned as a train driver or electrical engineer (both of which are barred to me), it's hardly an affliction. And I'm told it does have some advantages, which may explain why it continues to exist, in other apes as well as humans. There is a story (I don't know if it's true) that bomber crews used to like to take a colour blind crew member on board, because while they miss certain things, there are other things that they see rather vividly, and thus can pick out camouflaged targets. This may also apply to gathering fruit for apes. Certainly if I see gold against brown, the contrast is almost painful to me, with a shimmering line between the two, and I'm told that others (even some colour-blind people) don't get this effect, though I have heard it from some other colour-blind people.

Cheers,
Rat.I have heard also the stories about the bomber crews.

The perception of a given color, from a given stimulus, depends on both the wavelengths coming from the stimulus ("stimulus" broadly defined, including information both at and surrounding the target), and the sensitivity of the retinal cells to those particular wavelengths. Paints (including camouflage colors) that are blended to reflect a particular spectrum, may come up with, say, a particular green with several different combinations of pigments. That green may be the result of essentially a single wavelength of light, or a combination of two, three, or many wavelengths, each combination resulting in the same combination of signals from the three photopigments. If, however, you change either the sensitivity of the retinal photopigments (as with Rat's colorblindness) or the light illuminating the paint, colors that looked identical now can look terribly different.

Anyone can see this--it does not require getting rid of a set of cones--by visiting your local paint store. Most have learned that they must have a display that allows customers to see how different paint colors look when combined (walls & trim, for instance), and will have 3 or 4 different light sources to use for this purpose. Natural sunlight, incandescent light, fluorescent light, and perhaps one or two others I can't think of right now, each give a very different spectrum to reflect off of the paint samples. (Greens are particularly difficult to match under both incandescent and fluorescent light.) The spectral curves of the light sources are very different--the full spectrum of sunlight, the "redder" incandescent light, the discrete peaks of the fluorescent spectrum. Paints which look like a good match in sunlight can look horrible in fluorescent light (similar effect--take photos of someone's face, with no camera flash, by sunlight, incandescent, fluorescent, candlelight, and compare them).

Dang, I am wordy. Bottom line is, what looks like a match to a trichromat may stand out brightly to a dichromat.

[alfaniner]

The optical Illusion Benham's Disk (http://www.michaelbach.de/ot/col_benham/index.html) should be mentioned here. You spin a wheel made up of nothing but Black and White markings, and colors appear. Interesting references there for articles on "subjective colors." I'd like to know if color blind people see colors in it they've never seen before.

Nope -- nuthin' but black & white circles.

[gumboot]

An amazing such illusion appears in a BBC documentary about the brain. It's two girls in the same room, but one appears to be twice as big as the other. When they move next to each other you realize they are of the same height. The furniture and the walls in the room have been scaled so as to create that illusion.


You get some really trippy effects like that in film using foreshortening (using a lens with a long focal length which reduces depth perception and "Squashes" the image).

Like in the film Lord of the Rings...

When Frodo and Gandalf are riding on the cart they're actually about 14 feet apart. Similar in the scene where Gandalf and Bilbo are having tea at Bilbo's house.

Completely weird on set to see these actors performing scenes at opposite ends of a room....

Just had to trust PJ knew what he was doing!

-Andrew

[Beerina]

Also, if you've stared adequately long at the dot and then look at a different part of the image then the colours do disappear; but looking back at the dot makes the colours fade back in. It's very strange, I love it!

I notice a similar issue with the ring of pink dots. If you try to follow the green dot, it disappears. This seems to indicate that this is a physiological "burn in" issue rather than some mental trick of the brain. Like smell receptors, perhaps the rods and/or cones need a few seconds to relax without stimulation in order to feed the purest signal again, rather than a corrupt negative signal?

[Deetee]

Here (http://www.metacafe.com/watch/20665/ambulance_illusion/) is another illusion like the Gardner dragon.

[Touched]

Anywhere else the ambulance video can be seen? That bloody site just shows me a commercial, and then displays nothing.

[Odin]

http://forums.randi.org/imagehost/427844a04538ac223.gif

Its a variation on the afterimage illusions. As far as I can tell it works by the afterimage removing the smaller areas of the opposite colour.

[Almo]

She undoubtedly doesn't have enough eyeball control to keep her focus stationary for long. Can she see the hidden pictures in stereograms?

I have loads of eyeball control, and it took me years to see stereograms. My problem is there are two ways to set them up: 1) crossed eyes see it correctly 2) eyes drifted apart see it correctly. It was determined by someone that the best way was method 2). I can't drift my eyes apart, but I can easily cross them and hold them there. It ocurred to me that crossing should work once I saw some stereograms that were made of visible patterns instead of dots. Then I could see them easily, though the 3D was backward. :) BTW... I've played the StereoQuake mod, which displays two side-by-side views. Cross your eyes quite a lot, and you get full 3D quake. Was great for about 15 min when the headache set in. :D

[MetalPig]

I can't drift my eyes apart, but I can easily cross them and hold them there.
I can cross, but then I can't focus. Fortunately the drifting works for me, although sometimes I need to remove my glasses (and get real close to the picture :D ).

[GreedyAlgorithm]

Long lasting illusion (http://research.lumeta.com/ches/me/)

Cribbed from boingboing. It's been going strong for 10 minutes now, and the claim is that it will last for at least several hours.

[Bradk3]

Long lasting illusion (http://research.lumeta.com/ches/me/)

Cribbed from boingboing. It's been going strong for 10 minutes now, and the claim is that it will last for at least several hours.
The bars in my cell are all green now...

[Badly Shaved Monkey]

This is what convinced me:
http://forums.randi.org/imagehost/59414490fc75975c9.jpg

The wierd thing is that when you use the color grabber on the B square, it still looks much darker.

Do other people get this effect?

When I first looked at this image with the 'bridge', I still saw A darker than B and the bridge's darkness graded as it past through the 'shadow' of the cylinder. But, then I could feel my eyes doing something like what they do with those 'magic eye' 3-D images and A, B and the bridge suddenly became all the same shade but now they were somehow disconnected from the underlying board, seeming to float slightly above it.

[69dodge]

Long lasting illusion (http://research.lumeta.com/ches/me/)

Cribbed from boingboing. It's been going strong for 10 minutes now, and the claim is that it will last for at least several hours.That's just nuts. I looked at it yesterday, and I still get the illusion now, over 20 hours later.