Authors: Monika A. Koperska, Kamil Klinowski
The perception of the world, our conclusions on its functioning and almost all the biological processes of Homo sapiens are greatly determined by senses that we have been equipped with by mother nature in the course of evolution. Sight is our main cognitive tool – the majority of information transmitted to the brain comes via our eyes.
We can see objects that surround us thanks to the light that is electromagnetic radiation, and more specifically merely 1/34000 of the entire spectrum. This limited portion is called a visible spectrum, but science is aware of many more types of light, from radio waves to gamma rays. Depending on the length of an electromagnetic wave i.e. the amount of energy “carried” by photons, radiation may interact with matter in different ways. For example, if we saw the world in the spectrum of radio waves, we would not be able to see our immediate environment and each other. Radio waves are simply too long – it is as if we wanted to touch bacteria with our finger. If we saw the world in the spectrum of mid-wave and far-wave infrared light, we would notice spots of heat, in X-rays we would only see walking skeletons, and in gamma rays only a snowy background because high-energy gamma photons pass through matter as they would pass through fog.
The long journey of photons
Sunlight travels a long way before it reaches the eye. It takes 8 minutes and 23 seconds to travel through the vacuum, then it breaks through the atmosphere and, in its filtered form, lights up the objects that surround us. The atmosphere absorbs the majority of gamma radiation, part of ultraviolet radiation and a great part of infrared radiation, making it possible for the light from a visible and radio spectrum to easily light up the surface of the globe.
The atmosphere that surrounds planet Earth lets the UVA and UVB radiation, visible light, near-infrared waves and radio waves through. The remaining part of an electromagnetic wave is absorbed. (Source: chandra.harvard.edu)
Then the visible spectrum photons that reach us from the Sun interact with the objects that we are surrounded with. Pigments that are contained in the objects absorb light with specified wavelengths. Colours that we see are actually colours that are complementary to the colours that were absorbed by the pigments. A carrot seems to be orange because β-carotene that is found in it absorbs blue and turquoise light. Chlorophyll a and chlorophyll b absorb blue and red radiation from the visible range, making it possible for the green light to reach our eye.
The curves show the amount of light from the visible spectrum absorbed by chlorophyll a, chlorophyll b and carotenoids. (Source: www.uic.edu)
From camera obscura to the entire eye
Visible light reflected off the objects, so that it carries the information about their properties, reaches the eye, which as far as physics is concerned operates exactly like camera obscura. A light waves passes through the cornea, spreads to the anterior chamber and the lens, where it becomes focused, and then through the vitreous body lands on the chemical detectors contained in the light-sensitive receptors of the retina – cones and rods.
A reverse image of objects that are in front of us and are lit up is created on the surface of the fundus. Computer simulations of the eye’s evolution suggest that as many as 250 thousand generations are needed to create this complex structure from simple light-sensitive cells and protective cells.
Therefore, the eye is the second filter after the atmosphere that affects the information on its way to the brain. The human eye consists of 95% water.
Literally speaking, we wear water glasses and we see only that part of the spectrum that is not absorbed by water molecules. The graph below illustrates the fact that only visible and ultraviolet spectrum photons may break through the water barrier. Such a strong relationship between water and our perception of the world is the result of evolution, because life on Earth itself developed in water.
The curve presents the amount of light absorbed by water within the spectrum ranging from ultraviolet to infrared inclusively. The “light slot” that lets the visible through has been marked with colours of the rainbow. (Source: www.lerepairedessciences.fr)
Colours in water and on land
The Earth was an extremely inhospitable habitat hundreds of millions of years ago. The first living organisms could develop only in water, which absorbed the majority of lethal cosmic rays and harmful UV rays (extremophiles, gas vents). Nautilus (of the order Nautilida, a mollusc inhabiting warm oceans) that inhabited these ancient waters could see thanks to a pinhole camera filled with water. Later on, approximately 700 million years ago, various types of light-sensitive cells, called cones, that specialise in capturing the light in a very narrow spectrum, evolved in our ancient ancestors. A slow process of eye tissue development took place in parallel with the evolution of light-sensitive cells. During its course, the detectors were gradually encased by groups of cells which served protective and optical purposes, such as the pupil and lens. These organisms had cones that perceived ultraviolet, blue, yellow and orange-red light. Rods, which specialise in shape recognition and movement perceptions, emerged only 200 million years later. In the course of time, ultraviolet and orange-red cones in our ancestors disappeared. In some primates (humans included), red detectors became differentiated. Owing to this change, we are able to perceive many more shades of green, which was of paramount importance, for example in assessing the ripeness of fruit and leaves.
Humankind vs. the rest of the nature
Accordingly, we are able to see in a very limited part of spectrum that was selected as the most useful for survival in the course of evolution.
Other organisms, such as birds and insects, retained for example the ability to perceive ultraviolet light.
From the perspective of an insect, the ability to recognise a plant which is suitable for pollination is crucial for survival, so insects have a cone that is sensitive to that particular light spectrum. Pollens and some parts of the flower calyx itself have quite different colours in the near-ultraviolet light spectrum that are literally unimaginable for us. A majority of birds have four cones that provide them with the information crucial for hunting for food (game trails, flower colour). We may also encounter some living fossils, such as Odontodactylus scyllarus, also known under the charming name of stomatopod, which has 16 types of light detectors that enable, among other things, polarisation vision.
Stomatopoda are a specific order of marine crustaceans that have 16 types of cones:12 are responsible for colour recognition and the remaining ones, among other things, for polarisation vision. (Source: www.wikipedia.com)
What happens next with the information?
It turns out that only 20% of a subjectively perceived visual scene consists of raw sensory stimuli! The brain processes visual information extensively and sets it in the context based on our previous experience. A background effect that may be observed when using colourful lighting is a typical example of this unconditional (top-down) interference. In colourful light, shades are not grey; they are of the colour that is complementary to the light colour. Remembering the lighting conditions that were present during previous observations allows the brain to quickly calibrate the “white balance”, for example when moving to a room that is lit differently. Objects that we are very familiar with retain a subjective colour stability.
Therefore, a colour is not merely a length of the electromagnetic wave, but rather a very complex perception. The world of colours comes into being due to constant operations of the brain. The brain interprets the “sets” of light that reach it with regard to the shape, surrounding colours, background colour and other properties of a given situation.
Other factors that affect colour perception include gender, current emotional state, language, cultural background (it will be discussed later) and memories. Mother nature provided women who used to gather food in the past with much greater colour sensitivity than men, who are better at perceiving movement. Some women have not just three but four cones; it allows them a far more precise differentiation of hues between green and blue. Also the emotions such as sadness, joy, anger, self-confidence, or embarrassment affect the ability to perceive shade differences between colours. Although science is continuously improving our understanding of sight, at some point we still reach the border of subjectivity, which means the inexpressible. We are literally unable to establish whether two people perceive a given colour in the same manner.
What do you really see when you look at something?
Another example of cognitive processes’ influence on the perception is the role of language and cultural background in colour perception.
In the case of newborns, light-sensitive cells develop within the first three months; the process of naming colours properly may take a couple of years.
An African tribe – the Himba – living in northern Namibia, that is isolated from a modern cultural lifestyle, has been a source of interesting discovery.
In their language there are not 11 colour names as in English, but only 4 colours; they are different from the colours perceived e.g. by Poles, as well. ‘Zuzu’ stands for dark shades of red, blue, green and purple. ‘Vapa’ is shades of white and yellow, ‘Boru’ is pale blue and green.
‘Dumbu’ stands for shades of olive-tone green, red and brown. This range that is established in the visible spectrum in a different manner makes it more difficult for the Himba people to distinguish between pale blue and pale green (they are denoted by the same word) than for Europeans, to whom shades of green are hard to differentiate between. A language takes on its meaning when we perceive and define colours not as individual shades, but when we see them within the context of other colours. If we do not teach our brain to tell the difference between colours we will have problems with perceiving the differences between similar shades. Shopping is an example of such a situation: “What’s the deal with these blouses?
They are both red…”
Environmental circumstances and all the changes that affect electric impulses on their way from the eye to the brain significantly reduce our visual perception of the world. On the one hand, it should be admitted that the range of phenomena that we perceive has been selected in the course of evolution as the most advantageous with regard to survival, and optimised to the scale in which we operate. On the other hand, it is quite tempting to ask if there is a possibility to move the cognitive horizon a little further and increase our level of colour perception abilities? We are already able to take some advantage due to device miniaturisation and integrating the detectors into mobile devices. Projects such as Google Glass make us fully realise that devices similar to the Predator’s helmet or the Nite Owl’s vision goggles are almost at our fingertips. What is more, in the near future we may develop a technology that will allow for cybernetic integration of additional/substitute perception tools with, for example, infrared and ultraviolet detectors (human augmentation). In some respects, progress in this area seems to be not only a matter of time but also a matter of ethical decisions which will be taken by our civilisation. There is considerable evidence to suggest that we are on the brink of a cybernetic breakthrough; its consequences may dramatically change the way we perceive the world. Where will it take us?
We shall see.
Knowing human curiosity, we are not likely to wait for the answers for a long time…
Source: Granice Nauki