COLOURLESS LIGHT: SKY BLUE AND OTHER COLOURS ARE ALL IN THE MIND

THE ILLUSION OF COLOUR: AN EXAMPLE OF DISSOCIATIONIST PERCEPTION IN SCIENCE.

©2013 Federico I. Talens-Alesson

FOREWORD

This document supports the idea of colour fictionalism, elaborating on the question of why the colour of the sky is blue and the proposition that colours are created in the human mind. It is adduced as evidence of this being so that people who have consumed LSD perceive colours, sounds and smells that do not exist outside them, and on the nature of altered colour perceptions, and in particular of tritanopia. While amongst philosophers colour fictionalism has a following, this is not generally the case, and perusing physics and physiology tracts it is evident that the basic position is that colour exists.

REFUTATION OF THE CLASSIC EXPLANATION ON THE COLOUR OF THE SKY

The Classic view on why the sky is blue

The argument is based on a known physical phenomenon: Tyndall Effect. Simplifying, higher energy photons crossing a fluid medium, even a gas, have a higher probability of being deflected from their original trajectory. The deflection may also be by a larger angle. According to this, when light comes to us sideways and not from the direction of the sun, then the chances are that bluish-greenish photons would be more abundant than reddish-yellowish photons. This is also given as an argument for the prevailing green-blue colour of the earth from space, which is also attributed to Tyndall Effect.

Objections to the theory (I): Subliminality

While photons descending through the atmosphere travel some scores of km, photons coming sideways may have travelled hundreds of kilometres: that our focal distance prevents us from seeing far away objects does not mean that individual photons which have come from far away cannot be detected by our eyes. So the question is why should not those more frequent bluish photons be further deflected before they reach our eyes, while the less frequent yellowish photons manage to make it over longer distances. This should somehow balance photon distribution.

Also, we have to consider that air, not being a continuous fluid (molecules of gas are separated from each other, unlike in liquids) provides an uneven and changing pattern for the positions of those molecules that are a) deflecting a photon; b) deflecting it in the direction of the beholder's eye and c) deflecting it so that it arrives simultaneously with the other photons of a given “image”.

Therefore, we are seeing a series of differently positioned sets of points of different “colours” against a background of “no light”. It should be obvious that no individual image will “last” enough to be perceived: all off them will be subliminal images. Therefore, we should not be seeing any of them.

Although each image should be a series of colour points on a black background, the perception of light works in such way that the brain decides to see “white light” if a threshold of incoming radiation has been reached. Beyond that point, another threshold is reached where we see colours Therefore, we should be aware of the incoming of enough photons to generate the idea that there is light, but not the presence of specific colours because of subliminality, even if there is a predominant colour amongst them.

Figure 1. Top: More easily deflected photons coming from further away again have a higher probability of being further deflected.  Bottom: photons coming into the eye at a given time do not need to have the same colour distribution over the vision area. Neither any of the "images" can last enough to be consciously observed.

Objections to the theory (II): Tritanopia and LSD as proofs of subjective assignment of colour to light wavelengths.

Tritanopia is a case of altered colour perception. Unlike the forms of Daltonism, it is not hereditary, and affects both women and men, with a frequency of about 1 in 10,000. The particular characteristic of tritanopia is that the persons affected perceive substantial amounts of blue colour in the region they also perceive yellow. And they have a weak perception of blue when normally sighted people would see this colour This leads to yellow being perceived as white, red and orange being purplish and rosey-purplish, and green being bluish green. Blue is also a bluish green hue, and violet is again purplish. See Figure 2.

Figure 2 Top left: tritanopia “rainbow”. Top right: result of removing blue from tritanopic spectrum. Bottom right: Normal sighted. Bottom left: result of adding blue to normal sighted. It can be seen that tritanopic and blue-loaded “normal” differ in the three bottom colours. On the other hand, removing blue from tritanopic spectrum leaves the four top colours equal from normal sighted. The difference between tritanopics and normally sighted is then that tritanopics perceive substantial blue over the four top colours and less than normal for the two bottom colours.

Colour is detected by cone cells in the eye, which change their electrical properties due to state transitions in specific molecules present in them. The brain receives the result of these conductivity alterations and then makes its on decisions on what colour to flag as “seen”. Notice that the photon does not “travel” through the optic nerve: the only evidence the brain has of a incoming light event is that conductivity in the cells involved in detecting it has changed.

Tritanopia is regarded as the consequence of an absence of S cones. But the fact is that a tritanopic spectre is composed of a region where blue is not seen sufficiently (the blue-violet range) and a region where it is seen and should not (the red-green range). There would be an explanation (Figure 3): the neurons which should be processing S cone signals are now processing M or L cone signals, which causes them to respond to a long wavelength detection input by producing blue colour. That is, the colour created by the brain is consequence of an input which has nothing to do with the wavelength.

Figure 3. Spectra for normal colour perception and several partial colour blindness  It can be seen that they all could be explained by brain cells being connected to the wrong kind of cone cells in the absence of one of the kinds. (From http://jfly.iam.u-tokyo.ac.jp/color/)

Protanopia and deuteranopia, respectively the absence of L and M cone cells would also lead to the same “wrong wiring” problem, in which M cells would be wired to the brain as L or even S cones and vice versa.: L cones would be wired as M or S cones.

Therefore, colours do not depend on the actual energy of the light detected, but on what sensors are available and how they are wired to the brain. Tritanopia and Daltonism show that the connection between light and colour is not direct, but subjective. This is reinforced by evidence from people who have experimented with LSD: they perceive colours, sounds and even smells which are “not there”. Stimuli sent by means of a variety of stimuli lead to the occurrence of colour in the mind.

Tritanopia is the condition on which I have focused because it relates to the “right” colour: blue. There is no obvious reason to reject the idea that, by default, normally sighted people are affected by an altered perception of colour themselves. In particular, the perception by default of a small amount of blue colour in the absence of actual colour perception. To begin with, in conditions of twilight, it would be hard to see how to differentiate between black and white vision (as it is assumed to happen) and black and pale blue vision. I discuss this in the next section.

Objections to the Theory(III): Colours do not add up.

Let us go back to the idea that the Tyndall effect is behind the colour of the sky and also the planet. The theory is that the Sun emits white light, some of it is scattered (blue/green) and that gives the colour of Earth from space.

There is a problem: if some blue-green light is bounced back into space, then the light within Earth's atmosphere should be yellower-redder (Figure 4). This means that the light coming straight down would be even redder, because some additional blue light would be deflected at least sideways. Nevertheless, at any point of the atmosphere, the composition of the radiations crossing there from any directions will be still yellower-redder than the original sun light, and conform to the resultant of white light minus of outbound lost blue-green. Which means we ought to see the clouds (which are scatterers of light) yellowish.

Figure 4. Top: the white light of the Sun. Middle: Upwards scattering causes the light to become yellower. Clouds, by interception downfalling light and laterally scattered light  should themselves scatter an averaged yellowish light. As discussed above, the sky should not have a colour, only be light/white. Bottom: the brain adds by default some blue: the sky turns blue and the late morning clouds are white.

But we see them white during normal daytime. And we see the sky blue. A default shift to blue by our brain would explain that: yellow clouds would be white, and white sky would then be blue. There is no obvious reason why the default value for an arbitrary creation of the mind to have a zero default value. Of course, there is also the question of whether the Sun is actually emitting white light, and not yellow, and that we think it is white because of own blue correction. This would mean that, if there were colours (which I propose there aren't), then Earth would actually be mostly a shade of yellows, with water being white (we would see it blue partially because of our eye correction) and landmasses yellow (we would see them green because of our blue correction) or yellow-reddish.

SENSES AND PERCEPTION.

Our ears contain a membrane which vibrates under shock waves, and causes two tiny bones to action. This causes again vibration to a fluid-filled conduit, which in turns fires nerve response through its fluctuation. There are here two disconnects: whatever change between the original vibration propagated through air and the vibration in the liquid-filled conduit, and whatever correlation exists between the second vibration and the response triggered on the nerves. Together with our knowledge that people under the influence of LSD “hear” sounds, then the actual sound is created again in our mind, exactly as colours The same would be the case with smells.

However, even though logically we should see this to be the case, the usual perception is that colours, sounds and smells exist by themselves. This is much influenced by empiricist and pragmatist mentalities, and in particular by the tendency to dissociate phenomena, leaving out aspects of it, and to support the idea that particular conditions and exceptions abound.

For example, while in principle the fact that colour generation can be triggered chemically through the blood streams feeding the brain cells should suggest that stimuli from the nervous systems also trigger colour generation as an internal brain experience, it would be typical from an empiricist point of view to claim that chemically induced, internal generation of colour is an aberration, and that all other means of colour perception relate to an outside existence of colour, ignoring the fact that light received by the eye ceases to be an active part of the phenomenon of sight once it excites cone cells, and from then on it is about electrical change across the nervous system.

A typical example of this dissociative outlook is attributing to the properties of the chemicals in the cone cells the quality to define if a given colour of light is detected or not. There are about 5 million of cone cells (million more or less) per eye. That means that harvesting the photopsins from a human being would yield 10 million molecules. Thus, for a micromol of each photopsin so that we can conduct a spectrophotometric test, which is roughly half a million billion billions of molecules, we would need the eyes of 50 thousand billion human beings. Obviously, this has not been done.

What testing has been done has involved the response of the combination of the human eye, the optic nerve, and the brain of individuals. While certain conditions can be isolated and a particularity of perception related to them (people without a lens in their eye sometimes can see UV), the fact is there is no reason to reject the idea that the brain decides to acknowledge certain values of voltage for certain photopsins, consequence of the wiring of the cone cells to it through the nervous system.

This dissociation is something which I found at the time of publishing my last papers in chemistry journals and my first blogs (as a consequence of being unable to carry on publishing). The underlying subject (unrelated to the present topic) was that a given property called the surface excess of a chemical in solution (its concentration at the surface of the liquid, so to say) was responsible for a number of phenomena: solute-related light absorption of a solution and solubility of solutes in solvents, to name two. Reviewers with a dissociationist perspective (strong in chemistry where it is very common for practitioners to deny that there can ever be an underlying factor to a range of phenomena).

As a consequence, more than in discussing “realist” perceptions (whether colour exists or is a figment of our imagination), I thought this exercise would be useful to illustrate dissociationist perception: the overlooking of factors which should be taken into account when trying to find an explanation for a phenomenon.