Neat optical illusion

[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]

The Sensation of Color

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? 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]

The Castle Illusion uses the afterimage effect

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.

 

[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? 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) 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 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)

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 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]

Sensations for Zombies

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 by Todd C. Moody, from The Journal of Consciousness Studies. Are deniers of sensations and consciousness zombies themsleves? My own father -- a Zombie???? 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 by Todd C. Moody, from The Journal of Consciousness Studies. Are deniers of sensations and consciousness zombies themsleves? My own father -- a Zombie???? 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!