romansh wrote:...
Also just before you go to sleep in a dark room do you see faint colours?

I don't get that effect myself, and I'm not sure what might cause it. Tell me more - which colours do you see, and are they always the same, irrespective of what you have been looking at before you shut your eyes? Also, are they patterned in any way?

I get all sorts of weird shapes and colors in my left eye when I close it. But that's due to Ischemic Optic Neuropathy, which killed off a bit of the optic nerve and destroyed one quadrant of my vision. It probably would be a good idea to see an ophthalmologist.

laklak wrote:I get all sorts of weird shapes and colors in my left eye when I close it. But that's due to Ischemic Optic Neuropathy, which killed off a bit of the optic nerve and destroyed one quadrant of my vision. It probably would be a good idea to see an ophthalmologist.

You diagnosed yourself with Ischemic Optic Neuropathy without an ophthalmologist? That's impressive!

DavidMcC wrote:
Romansh, why would there have to be any "yellow" photons, when your LW (red) and MW (green) cone cells can be equally stimulated with a spectrum which has only, say red and green photons, or a whole range of mixtures that happen to give the same cone cell response as monochromatic yellow? ...

This is exactly my point the monitor is not emitting any yellow photons ... our experience of yellow is an illusion.

romansh wrote:

DavidMcC wrote:
Romansh, why would there have to be any "yellow" photons, when your LW (red) and MW (green) cone cells can be equally stimulated with a spectrum which has only, say red and green photons, or a whole range of mixtures that happen to give the same cone cell response as monochromatic yellow? ...

This is exactly my point the monitor is not emitting any yellow photons ... our experience of yellow is an illusion.

I wouldn't call it an illusion myself, because it isn't really misleading you, rather, it is the result of the compression of the colour spectrum into just three colour signals, which form a simple spectrometer, which has to simplify any complicated spectra. Illusions only occur when those signals are effectively distorted by various factors, that have been described in the optical illusions thread fromn a couple of years ago.

laklak wrote:I get all sorts of weird shapes and colors in my left eye when I close it. But that's due to Ischemic Optic Neuropathy, which killed off a bit of the optic nerve and destroyed one quadrant of my vision. It probably would be a good idea to see an ophthalmologist.

I was diagnosed with idiopathic optic neuritis back in 2005. The weird shapes have all but gone now. It was like a monochromatic Inuit drawing. I also experienced the shapes on any large plain background (often the sky). I was effectively blind in one eye for a few weeks. Luckily the vision has come back to all intents and purposes.

For those people who do not experience colours in the dark.
https://en.wikipedia.org/wiki/Closed-eye_hallucination

DavidMcC wrote:
I wouldn't call it an illusion myself, because it isn't really misleading you, rather,

I know it is a mixture of three relatively monochromatic colours none of which are yellow.

If you don't call it an illusion, fine.

There are many, many eye conditions:
http://www.allaboutvision.com/conditions/
Sorry to use a .com, but 'this is the best list I could find on the www.

EDIT: OK, some of them aren't really eye conditions, but many are.

DavidMcC wrote:
You diagnosed yourself with Ischemic Optic Neuropathy without an ophthalmologist? That's impressive!

Lol no, I meant if you're seeing weird colors you should probably consult a doctor, I should have been more precise. One tends to seek medical attention when one wakes up partially blinded with no warning or other symptoms.

romansh wrote:
I was diagnosed with idiopathic optic neuritis back in 2005. The weird shapes have all but gone now. It was like a monochromatic Inuit drawing. I also experienced the shapes on any large plain background (often the sky). I was effectively blind in one eye for a few weeks. Luckily the vision has come back to all intents and purposes.

Mine are generally swirly, twisty lines and shapes that almost appear 3 dimensional, usually a yellow-white color, and cloud-like splotches of multiple colors that grow and fade. I can almost see dead Cthulhu, dreaming in R'lyeh. I've regained a bit of vision in that quadrant, not much but I can now detect peripheral motion.

romansh wrote:

DavidMcC wrote:
Romansh, why would there have to be any "yellow" photons, when your LW (red) and MW (green) cone cells can be equally stimulated with a spectrum which has only, say red and green photons, or a whole range of mixtures that happen to give the same cone cell response as monochromatic yellow? ...

This is exactly my point the monitor is not emitting any yellow photons ... our experience of yellow is an illusion.

You are making a mistake by generalizing from, "my photoreceptor can produce illusory outputs" to, "all of the outputs from my photoreceptor are illusory." I agree with the former claim, but not with the latter. The latter claim, your claim, is a non sequitur. Also, the illusion you're referring to doesn't happen in the brain, it happens in the eye. So even though it's an illusion, it has nothing to do with conceiving the color yellow. The conception of yellow happens in the optical cortices in communication with the frontal lobes following a bit of pre-processing in the retinas, magnicellular and parvicellular pathways, and via some feedback loops including- but not limited to- the brain stem and the hypothalamus. Lots of really complicated, completely automatic stuff happens to vision before we get to think about what we're seeing.

laklak wrote:If God didn't want red to be angry he wouldn't have said "nature, red in tooth and claw". Checkmate, atheists.

On a slightly different note, why do women paint their nails (or maybe "talons"?) the color of blood? Are they trying to tell us something? What's it mean?

Blame it on Rita and Revlon.

DavidMcC wrote:
EDIT: We do not need any words to be able to perceive colour, only to be able to talk about it.

There is actually evidence that shows that language has significant influence on what colors we perceive. The experiment with Himba tribe's people in the linked video is pretty telling.

http://www.boreme.com/posting.php?id=30 ... tCveZwrJhE

Your cultural language of color can make the difference between what colors are perceived as as different from other colors. What I might recognize as Blue-Green, another culture may only perceptive as Blue and no different from what I see as Blue.

So perceiving distinct colors is a learned behavior driven by our language of color.

CdesignProponentsist wrote:

DavidMcC wrote:
EDIT: We do not need any words to be able to perceive colour, only to be able to talk about it.

There is actually evidence that shows that language has significant influence on what colors we perceive. The experiment with Himba tribe's people in the linked video is pretty telling.

http://www.boreme.com/posting.php?id=30 ... tCveZwrJhE

Your cultural language of color can make the difference between what colors are perceived as as different from other colors. What I might recognize as Blue-Green, another culture may only perceptive as Blue and no different from what I see as Blue.

So perceiving distinct colors is a learned behavior driven by our language of color.

I regard this as bad scence, CdP, because why would only the Himba be able to "learn" not to see blue? More likely, it is as I described in an old thread of mine on the Himba's colour vision. Before intermarraige with the Herero tribe, they were likely all tritanopes, (insensitive to blue light, because the refractive index of the human lens starts to change in the blue, and this would slightly blur their distance vision - an important issue for a tribe that has to spot tiny dots on the (blue) horizon. I wrote a thread on this a few years ago. It's mainly biology, not learning, that affects their vision.

romansh wrote:Pragmatically London double decker buses can be considered as red, because we each have our own individual experience which may or may not be similar that we define as red. No one I think is arguing against this. The physics and biochemistry is not on the side of these buses actually being red.

...

Please explain the biochemistry and physics of why you think that red buses aren't actually red.

romansh wrote:

DavidMcC wrote:
I wouldn't call it an illusion myself, because it isn't really misleading you, rather,

I know it is a mixture of three relatively monochromatic colours none of which are yellow.

If you don't call it an illusion, fine.

Perhaps you missed the bit where I explained why seeing yellow without any monochromatic yellow being present is not a true illusion, unless you think that seeing almost any non-monochromatic colour, that involves significant excitation of more than one cone type is an "illusion". Rather, it isthe visual system limitting the number of different perceived colours, probably to limit the size of the visual cortex. If yellow is defined as any wavelength spectrum that leads to approximately equal firing rates of MW and LW cone cells, then seeing yellow without any photons that are at or near the monochromatic yellow wavelength is not an illusion, rather, it is just space-saving in the VC. If you see yellow under different conditions than this, THEN it is a colour optical illusion.

Don't for a minute hope that I haven't noticed this thread.

DavidMcC wrote:
Perhaps you missed the bit where I explained why seeing yellow without any monochromatic yellow being present is not a true illusion, unless you think that seeing almost any non-monochromatic colour, that involves significant excitation of more than one cone type is an "illusion". Rather, it isthe visual system limitting the number of different perceived colours, probably to limit the size of the visual cortex. If yellow is defined as any wavelength spectrum that leads to approximately equal firing rates of MW and LW cone cells, then seeing yellow without any photons that are at or near the monochromatic yellow wavelength is not an illusion, rather, it is just space-saving in the VC. If you see yellow under different conditions than this, THEN it is a colour optical illusion.

is not wrong. It looks like visual processing is an area in which I would not choose to tussle with DavidMcC. Not even for old times sake.

My understanding, courtesy of the relevant scientific research, is that colour perception depends upon a multiplicity of factors. First, it depends upon the wavelength of the light reflected from objects, that enters the eye, and which then triggers the requisite photoreceptor molecules. Second, it depends upon which photoreceptor molecules are present to be triggered.

However, even if we work with what might be termed a "standard" set of photoreceptors, colour perception is rather more involved than simple triggering of those photoreceptors by relevant wavelengths. This is illustrated by both the behaviour of colour photographic film, and the behaviour of early television cameras.

If you take a photograph of a scene in natural daylight, using a particular sample of film manufactured to reproduce colours faithfully under natural daylight, and then take a photograph of another scene, this time illuminated by a tungsten filament bulb, using that same film, you will notice a difference between the photographs after the film has been developed, and the positive prints produced. The scene photographed under tungsten illumination will feature an orange cast over areas of white. Likewise, using a film manufactured to reproduce colours faithfully under tungsten illumination, will result in natural daylight scenes having a blue cast over areas of white.

The same phenomenon affects early television cameras. Set up the camera to reproduce colours faithfully under one set of lighting conditions, and the moment that camera is moved to different lighting conditions, it will cease to reproduce colours with the same fidelity. The colours displayed on the television screen connected to that camera, will change constantly as the lighting conditions change when the camera is moved from point to point.

This is Part 1 of the requisite Horizon documentary covering this:



Parts 2, 3 & 4 are provided below:







Basically, what influences colour vision, is a combination of the spectral distribution of ambient light, and how much of that spectral distribution is reflected to our eyes by objects in our field of view. The relative proportions of red, green and blue light reflected remain constant across a wide range of spectral distributions, and these are integrated by the brain to produce colour constancy within those varying spectral distributions. Even spectral distributions that have some gaps in them, such as those generated by older fluorescent lighting, don't appear to fool the brain because of this integrative process, but they do impact heavily upon film - special fluorescent filters are needed to prevent weird colour casts appearing on daylight balanced film in an environment involving 1970s/1980s vintage flourescent lights. Only under extreme spectral distributions does the colour intergration system break down, such as monochromatic spectral distributions (which were useful in, for example, the Ole Seehausen experiments on sexual selection via colour in Lake Victoria Cichlid fishes).

The paper produced by Edwin Land (inventor of, amongst other things, the Polaroid camera), that presented the full details of the integrative process is this one:

Lightness And Retinex Theory by Edwin H. Land & John J. McCann, Journal of the Optical Society of America, 61(1): 1-11 (1971) [Full paper downloadable from here]

Land & McCann, 1971 wrote:Sensations of color show a strong correlation with reflectance, even though the amount of visible light reaching the eye depends on the product of reflectance and illumination. The visual system must achieve this remarkable result by a scheme that does not measure flux. Such a scheme is described as the basis of retinex theory. This theory assumes that there are three independent cone systems, each starting with a set of receptors peaking, respectively, in the long-, middle-, and short-wavelength regions of the visible spectrum. Each system forms a separate image of the world in terms of lightness that shows a strong correlation with reflectance within its particular band of wavelengths. These images are not mixed, but rather are compared to generate color sensations. The problem then becomes how the lightness of areas in these separate images can be independent of flux. This article describes the mathematics of a lightness scheme that generates lightness numbers, the biologic correlate of reflectance, independent of the flux from objects.

And the proof of the pudding from this paper, is that it has been applied to the business of automatic white balancing in cameras, and it works. Every digital camera in existence, still or video, uses this process to perform automatic white balancing.

So, colour as we perceive it, is actually an integrative phenomenon, relying upon a considerable amount of post-processing of the data by the brain. Although we can assign colours to wavelengths, on the basis that shining a light of a particular wavelength upon a white screen will produce the colour in question, our actual handling of colour in a xomplex environment is very much the product of our brains, and is aimed at ensuring colour constancy under a wide range of ambient spectral distributions - constancy that would be absent if we simply relied upon the raw signal data without the post-processing.

Which demonstrates that it pays to be rigorous when covering these topics.

DavidMcC wrote:

romansh wrote:

DavidMcC wrote:
I wouldn't call it an illusion myself, because it isn't really misleading you, rather,

I know it is a mixture of three relatively monochromatic colours none of which are yellow.

If you don't call it an illusion, fine.

Perhaps you missed the bit where I explained why seeing yellow without any monochromatic yellow being present is not a true illusion, unless you think that seeing almost any non-monochromatic colour, that involves significant excitation of more than one cone type is an "illusion". Rather, it isthe visual system limitting the number of different perceived colours, probably to limit the size of the visual cortex. If yellow is defined as any wavelength spectrum that leads to approximately equal firing rates of MW and LW cone cells, then seeing yellow without any photons that are at or near the monochromatic yellow wavelength is not an illusion, rather, it is just space-saving in the VC. If you see yellow under different conditions than this, THEN it is a colour optical illusion.

You are not addressing my question here.
I understand the process more or less.

Is a double-decker London bus red, or is it what we call the perception of the photochemical reactions and transfer of charge down the optic nerves that has been processed in the brain "red"?

The photons themselves are not red!

DavidMcC wrote:
I regard this as bad scence, CdP, because why would only the Himba be able to "learn" not to see blue?

Their language. That's the point. Did you watch the video?

Also it isn't that they can't see blue, its that they have lumped blue into the same part of the spectrum as green with one word to describe both. So to them the difference between blue and green is very subtle. To us it is dramatic because we have a word for Blue and a word for Green. They have a different categorization of the spectrum.

More likely, it is as I described in an old thread of mine on the Himba's colour vision. Before intermarraige with the Herero tribe, they were likely all tritanopes, (insensitive to blue light, because the refractive index of the human lens starts to change in the blue, and this would slightly blur their distance vision - an important issue for a tribe that has to spot tiny dots on the (blue) horizon. I wrote a thread on this a few years ago. It's mainly biology, not learning, that affects their vision.

I've searched for Himba and tritanopia and all I get is your thread. Do you have a source?

Also this wouldn't explain their ability to perceive the very subtle differences in shades of green other populations have difficulty with. Shades of green for which they have very specific primary names for.