Colours of Nature

Scientists have traced it all the way from the genes that prescribe color perception to the final expression of color perception in language.

Color does not exist in nature. At least, it does not exist in nature in the form of untutored brain thinks. Visible light consists of continuous varying wavelengths, with no intrinsic color in it. Color vision is imposed on its variation by the photosenstive cone cells of the retina and the connecting nerve cells of the brain. It begins when light energy is absorbed by three different pigments in the cone cells, which biologists have labeled blue, green, or red cells according to the photosensitive pigments they contain. The molecular reaction triggered by the light energy is transduced into electrical signals that are relayed to the to the retinal ganglion cells forming the optic nerve. Here the wavelength information is recombined to yield signals distributed along two axes. The brain later interprets one axis as green to red and the other as blue to yellow, with yellow defined as a mixture of green and red. A particular ganglion cell, for example, may be excited by input from red cones and inhibited by input from green cones. How strong an electric signal is that it then transmits tells the brain how much red or green the retina is receiving. Collective information of this kind from vast numbers of cones and mediating ganglion cells is passed back into the brain, across the optic chiasma to the lateral geniculate nuclei of the thalamus, which are masses of nerve cells composing a relay station near the center of the brain, and finally into arrays of cells in the primary visual cortex at the extreme rear of the brain.

Within milliseconds the visual information, now color-coded, spread out to different parts of the brain. Hw the brain responds depends on the input of other kinds of information and memories they summon. The patterns invoked by many such combination, for example may cause the person to think words denoting the patterns. ……

The chemistry of the three cone pigments – the amino acids of which they are composed and the shapes into which their chains are folded – is known. So is the structure of the DNA in the green of the X chromosome that prescribe them, as well as the mutations in the genes that cause color blindness.

So, by inherited and reasonably well understood molecular processes, the human sensory system and brain break the continuously varying wavelengths of visible light into the array of more or less discrete units we call the color spectrum. The array is arbitrary in an ultimately biological sense. It is only one of many arrays that might have evolved over thousands of millennia. But it is not arbitrary in cultural sense. Having evolved genetically, it can not be altered by either learning or fiat. All of the human culture traits involving color are derived from this unitary process. As a billogical phenomenon, color perception exists in contrast to the perception of light intensity, the primary quality of visible light other than frequency. When we vary the intensity of light gradually, say by moving a dimmer switch smoothly up or down, we perceive the change as the continuous process it truly is. But if we use monochromatic light – project only one wavelength at a time – and change from one wavelength to the next in succession, we do not perceive such a continuity. What we see is going from the short wavelength end to the long wavelength end is first a broad band of blue, then green, then yellow, and finally red. And to the colors white, produced by the colors combined, and black, the absence of light. ~ Page 205 to 207 (The Social Conquest of the Earth – Edward O Wilson)

Rich and seemingly boundless as the creative arts seem to be, each is filtered through the narrow biological channels of human cognition. Our sensory world, what we can learn unaided about reality external to our bodies, is pitifully small. Our vision is limited to a tiny segment of the electromagnetic spectrum, where wave frequencies in their fullness range from gamma radiation at the upper end, downward to the ultralow frequency used in some specialized forms of communication. We see only a tiny bit in the middle of the whole, which we refer to as the “visual spectrum.” Our optical apparatus divided this accessible piece into the fuzzy divisions we call colors. Just beyond blue in frequency is ultraviolet, which insects can see but we cannot. ….. Page 268

One question that stymied him (Leonardo) was why images do not appear to be reversed and inverted in the brains. L he had studied a device known as a camera obscura, and he knew that the image is produces is upside down and reversed because the lines from the object cross as they go through the aperture. Mistakenly, he assumed that somewhere deep in the eye or brain is another aperture that rights the image. He did not realize that the brain itself can make that adjustment, although his own ability to write and read in mirror script should have provided a clue. ~ Page 271