GrahamH wrote:Here you go David, try measuring "physical colour" of these green dots:

The above illusion is only possible with a TV screen, you realise. It requires rapidly flashing images.
What makes you think the green dots could not be measured as physical green, even though their subjective colour is very different.
Why do you think that this image (with which I have long been familiar) refutes a word I have been saying?

Graham, the flashing dot illusion is only possible with a TV display, such powerful hue illusions do not occur without technology, so our eyes are especially vulnerable, as we did not evolve with TVs. The purple dots are merely colour-inverted after-images from the green dot, which does not last long at any one point, although the after image does.

... Note that the purple subjective colour is related to, but not equal to the green colour of the physical dot. Can anyone produce a differently coloured image, to show how the perceived colour of the after-image is related to the colour of the physical dot?

DavidMcC wrote:

GrahamH wrote:Here you go David, try measuring "physical colour" of these green dots:

The above illusion is only possible with a TV screen, you realise. It requires rapidly flashing images.
What makes you think the green dots could not be measured as physical green, even though their subjective colour is very different.
Why do you think that this image (with which I have long been familiar) refutes a word I have been saying?

WTF? What green dots David? The only "physical colours" there are magenta and grey. Of course this illusion is not specific to "TV screen". The "flashing" is important of course, but you will have to show how anything anout colour in that illusion is specific to "TV screens".

It refutes what you are saying because colour is perceived that is not there in the physical system. Therefore at least this green colour is entirely in your head (as colour).

DavidMcC wrote:

crank wrote:...

'Yellow' and 'red' are in your head, ...

Nobody is arguing against that, crank. However, these colour perceptions only evolved in response to the existence of physical colour in the environment (light spectra), and we would not see colours if there were no such variable spectra.
Colour perception is, indeed, a subjective thing, but the variability is mainly in the shade, not the hue of the colour, as illustrated by the multicoloured cube that is often posted here. I still claim that perceived hue is based on, though not identical to, the physical colour of the light entering the eye. (This allows for optical illusions to change the perception without changing the physical colour of the light.)

Why do you never answer any of the issues raised? After 5 or more times, you haven't come up with an answer to the blind/sonar issue, you just bring up unrelated BS.

crank wrote:

DavidMcC wrote:

crank wrote:...

'Yellow' and 'red' are in your head, ...

Nobody is arguing against that, crank. However, these colour perceptions only evolved in response to the existence of physical colour in the environment (light spectra), and we would not see colours if there were no such variable spectra.
Colour perception is, indeed, a subjective thing, but the variability is mainly in the shade, not the hue of the colour, as illustrated by the multicoloured cube that is often posted here. I still claim that perceived hue is based on, though not identical to, the physical colour of the light entering the eye. (This allows for optical illusions to change the perception without changing the physical colour of the light.)

Why do you never answer any of the issues raised? After 5 or more times, you haven't come up with an answer to the blind/sonar issue, you just bring up unrelated BS.

So you think that's what this thread is supposed to be about??
Wow, you could have fooled me!

Bingo! You have no answer. You might as well be saying 'because god'

crank wrote:Bingo! You have no answer. You might as well be saying 'because god'

No answerr to what? I've answered the point about the coloured spots as persistence of vision (producing complementary colours). What more do you want? Oh, I knowm you just want to annoy me with nonsensical posts, right?

DavidMcC wrote:

crank wrote:Bingo! You have no answer. You might as well be saying 'because god'

No answerr to what? I've answered the point about the coloured spots as persistence of vision (producing complementary colours). What more do you want? Oh, I knowm you just want to annoy me with nonsensical posts, right?

Oh FFS, try addressing what was in the post

crank wrote:

DavidMcC wrote:

crank wrote:Bingo! You have no answer. You might as well be saying 'because god'

No answerr to what? I've answered the point about the coloured spots as persistence of vision (producing complementary colours). What more do you want? Oh, I knowm you just want to annoy me with nonsensical posts, right?

Oh FFS, try addressing what was in the post

As far as I am concerned, that's what I did. Are you just playing games? I have dealt with the green/purple spots issue that someone brought up. What other issue do you want addressed.
You seem to be trying to make me the issue, by pretending that I'm not addressing colour illusions.
Do you accept that I have at least dealt with the green/purple spots illusion that someone brought up? That was Graham butting in, so I suggest that you complain to him, not me.

crank wrote:

DavidMcC wrote:

crank wrote:Bingo! You have no answer. You might as well be saying 'because god'

No answerr to what? I've answered the point about the coloured spots as persistence of vision (producing complementary colours). What more do you want? Oh, I knowm you just want to annoy me with nonsensical posts, right?

Oh FFS, try addressing what was in the post

You see, there are different posts raising different issues, so you have to specify the post.

DavidMcC wrote:

crank wrote:

DavidMcC wrote:

crank wrote:Bingo! You have no answer. You might as well be saying 'because god'

No answerr to what? I've answered the point about the coloured spots as persistence of vision (producing complementary colours). What more do you want? Oh, I knowm you just want to annoy me with nonsensical posts, right?

Oh FFS, try addressing what was in the post

You see, there are different posts raising different issues, so you have to specify the post.

You are unable to thread backwards? I posted this and you haven't addressed anything in it. And you won't answer the blind/sound to color mapping issue.

DavidMcC wrote:Graham, the flashing dot illusion is only possible with a TV display, such powerful hue illusions do not occur without technology, so our eyes are especially vulnerable, as we did not evolve with TVs. The purple dots are merely colour-inverted after-images from the green dot, which does not last long at any one point, although the after image does.

Sure you got that right?

Veida wrote:

DavidMcC wrote:Graham, the flashing dot illusion is only possible with a TV display, such powerful hue illusions do not occur without technology, so our eyes are especially vulnerable, as we did not evolve with TVs. The purple dots are merely colour-inverted after-images from the green dot, which does not last long at any one point, although the after image does.

Sure you got that right?

Indeed he is wrong. The dots are magenta, the green is the "afterimage". Here's the same animation slowed down a lot.

GrahamH wrote:

Veida wrote:

DavidMcC wrote:Graham, the flashing dot illusion is only possible with a TV display, such powerful hue illusions do not occur without technology, so our eyes are especially vulnerable, as we did not evolve with TVs. The purple dots are merely colour-inverted after-images from the green dot, which does not last long at any one point, although the after image does.

Sure you got that right?

Indeed he is wrong. The dots are magenta, the green is the "afterimage".
...

OK, so I got it the wrong way round. Sorry, but colour-inverted after-images are the key to it anyway.

EDIT: Can you run it faster than "normal", please. IIRC, you just see a green dot going in circles, no purple dots. That was the real illusion, right?

... IIRC, the purple dots disappear, and you just see the green after-image. That was the real optical illusion. I forgot the details in the years that have passed since I first saw it. (The illusion being the disappearance of the purple dots, and the appearance of just one, green dot.)

EDIT: In other words, you messed up the illusion, so I messed up too.

I'm not sure why I should believe in subjective colour at all.

Colour is essentially light of a particular wavelength. It is an objective fact whether light is red or blue. If we managed to incorrectly identify red as blue that wouldn't mean there was some blue in our minds at the moment we made the mistaken perception. There was no blue, only red. What there was was a mistaken belief about the colour of the light. We were having the kind of experience that we would more typically have in the presence of blue. But blue isn't an experience, it's a colour.

The complication comes about because our vocabulary for talking about colours is based on our human colour discrimination abilities which is as much concerned with tracking the physical position of objects as correctly measuring actual colour. But fortunately we don't need to rely solely on them anymore, we have the means to measure colour accurately.

Chrisw wrote:I'm not sure why I should believe in subjective colour at all.

Huh? So how do you account for colour illusions.

Colour is essentially light of a particular wavelength.

That's what I have called ""physical colour". You seem to take the opposite view from some of the others here, who deny that physical colour exists - it's all in the brain, you know (and that's subjective colour).

It is an objective fact whether light is red or blue. If we managed to incorrectly identify red as blue that wouldn't mean there was some blue in our minds at the moment we made the mistaken perception. ...

There was no blue, only red. What there was was a mistaken belief about the colour of the light. We were having the kind of experience that we would more typically have in the presence of blue. But blue isn't an experience, it's a colour.
...

A) I suspect that that is a bad choice of colour - it's hard to get those two mixed up.
B) It sn't just a matter of "belief", it's a matter of perception. If it was belief, you could be taught to see the wrong colour, and that doesn't happen, IMO, because colour perception occurs in the VC, but beliefs don't - they occur in the PFC, I suspect, where intellectual decisions are made.

Chrisw wrote:I'm not sure why I should believe in subjective colour at all.

Colour is essentially light of a particular wavelength. It is an objective fact whether light is red or blue. If we managed to incorrectly identify red as blue that wouldn't mean there was some blue in our minds at the moment we made the mistaken perception. There was no blue, only red. What there was was a mistaken belief about the colour of the light. We were having the kind of experience that we would more typically have in the presence of blue. But blue isn't an experience, it's a colour.

The complication comes about because our vocabulary for talking about colours is based on our human colour discrimination abilities which is as much concerned with tracking the physical position of objects as correctly measuring actual colour. But fortunately we don't need to rely solely on them anymore, we have the means to measure colour accurately.

It I highly ambiguous to call wavelength "colour". We have colour vision. Colour is what we see. We see green dots when there is not a green spectrum of light. We can for many colours we can make them from wildly differing spectra because all that makes it a colour we can see is the balance of cone stimulation, scene context and expectation. You simply can't ignore some of these factors and assert that what's left (e.g. wavelength) "is colour".

I'd much rather use a different word than colour for light spectra in a discussion such as this.

GrahamH wrote:

Chrisw wrote:I'm not sure why I should believe in subjective colour at all.

Colour is essentially light of a particular wavelength. It is an objective fact whether light is red or blue. If we managed to incorrectly identify red as blue that wouldn't mean there was some blue in our minds at the moment we made the mistaken perception. There was no blue, only red. What there was was a mistaken belief about the colour of the light. We were having the kind of experience that we would more typically have in the presence of blue. But blue isn't an experience, it's a colour.

The complication comes about because our vocabulary for talking about colours is based on our human colour discrimination abilities which is as much concerned with tracking the physical position of objects as correctly measuring actual colour. But fortunately we don't need to rely solely on them anymore, we have the means to measure colour accurately.

It I highly ambiguous to call wavelength "colour". We have colour vision. Colour is what we see. We see green dots when there is not a green spectrum of light. We can for many colours we can make them from wildly differing spectra because all that makes it a colour we can see is the balance of cone stimulation, scene context and expectation. You simply can't ignore some of these factors and assert that what's left (e.g. wavelength) "is colour".

I'd much rather use a different word than colour for light spectra in a discussion such as this.

You can ignore physical colour if you like, Graham, but the stripes of the rainbow of monochromatic colours make "colour" a suitable word for them, IMOk provided the qualifier is either present or implied.