Sense of sight – the eye, light and colour

The eyes are often called the most important of the sensory organs, and they are the ones most openly displayed on the face. "Seeing" is used almost as a synonym for "observing" or "understanding". Yet in the strict sense the eyes perceive only colour, light and dark. Shapes, motion and proportions are seen because the eyes move and work together with the senses of movement and balance.

Seeing and thinking

Visual impressions are easier to shut out than smells or tastes: closing the eyes is enough. There is a distance between the observer and what is seen, and that distance makes seeing a more conscious activity than the other senses. Of all the senses, sight contributes most to wakeful awareness. Human beings think, and thinking is intricately bound up with the act of seeing.

This also means that it is easier to be mistaken about what one sees than about what one smells. Sometimes thoughts decide what is seen. Ambiguous figures, in which the same lines can be read as two different things, make this tangible: the image flips as soon as the viewer thinks of the other possibility, although nothing on the paper changes.

The sense of sight is also the favourite sense of science. Almost everything is expressed visually, often in numbers read from a scale or a screen, because the eyes are held to be more reliable than smell and taste, which are sometimes called "more primitive". The eyes are considered objective. The phenomenological approach takes this seriously, but it also asks what is lost when the other senses are left out of an observation.

How the eye is built

The eye is a transparent, roughly spherical ball into which light enters. Light first passes through the cornea and then through the pupil, the opening in the centre of the iris. The pupil narrows in bright light and widens in dim light. Behind the pupil the lens focuses the light, which then crosses the eyeball and falls on the retina at the back.

The eyeball is filled with a transparent, colourless, jelly-like substance, the vitreous body, which consists almost entirely of water. The tissue of the cornea has a regular, somewhat crystal-like structure, which is why it is clear. The light-sensitive part of the retina contains two kinds of receptor. The rods sense light and dark and work even in very faint light. The cones are sensitive to colour and need more light.

The rods adapt well to changes in light. Anyone who walks into a darkened room at first sees nothing, but after a while can make out quite a lot and find the way around. In the dark, however, colours cannot be seen: that is the work of the cones. The yellow spot, or macula, is the most sensitive part of the retina and its centre consists solely of cones. The place where the bundled optic nerve leaves the eye is called the blind spot, as there are no receptors there to register anything.

Two eyes that move

The eyes are never still. Even when a person fixes a point, they make small, rapid jumps, and when reading or looking around a scene they leap from one point to the next several times a second. Only the centre of the retina sees sharply, so the picture of a whole room is built up from many short glances. What seems a single calm image is the result of constant movement, which is why the sense of sight depends so closely on the sense of movement.

The two eyes also look from slightly different positions. Each receives a slightly different picture, and from the difference between the two the depth of a scene is judged. Covering one eye makes it harder to pour water into a glass or to thread a needle. Distance is further read from other signs: nearer things cover farther ones, far objects look hazier and bluer, and the eyes turn inwards more for close objects than for distant ones.

Animals show how much the position of the eyes says about a way of life. Hunting animals such as cats and owls have eyes facing forward and see depth well in front of them. Prey animals such as horses and rabbits have eyes at the sides of the head and overlook almost their whole surroundings, at the cost of a smaller field in which both eyes see together. The pages on mouse, lion and cow and on dog and cat describe such differences in more detail.

Colour

Along the spectrum people can distinguish roughly 150 hues, and some people more; with differences in brightness and saturation the number of distinguishable colours becomes far larger. The eye is particularly fine in telling apart shades of green. Some people are partly colour blind: they lack one type of cone or have a weakened one, and then confuse red and green, for instance. Test plates with coloured dots in which a number is hidden show this at once.

Colours affect mood. Red makes people active; it is experienced as lively and restless and gives a sense of strength and energy. Orange makes people enthusiastic, while yellow radiates and gives a sense of cheer. Green is restful and balanced. Blue is a cool colour and stimulates thought. White is felt as purity, and in many cultures it symbolises innocence. Black, on the other hand, is associated with sorrow and mourning.

Goethe: colour between light and dark

Goethe argued that colours arise from the interplay of light and darkness. Red, orange and yellow appear when one looks out of the dark, through something dim, towards something light, as with the setting sun seen through the thick layer of air near the horizon. Blue and violet predominate when one looks from the light at something dark. That is why the sky is blue: it is light here on earth, but black in space.

In Goethe's words, light's victory over darkness gives the active colours (red, orange and yellow), while darkness winning over light brings out the passive colours (blue, indigo and violet). A rainbow can be read in this way. The sky outside the bow is darker than inside it, and the red always lies on the outer, darker edge and the violet on the inner, lighter one. Brown eyes are sometimes cited as another example, with the iris reddish near the pupil and greenish or bluish near the white of the eye.

Goethe's theory of colour was not a replacement for Newton's physics of the spectrum, and physicists did not adopt it. Its strength lies elsewhere: it describes how colours appear to an observer and under what conditions, and in that sense it has remained a model for phenomenological observation.

Colours can be arranged in a circle in the sequence red, orange, yellow, green, blue, indigo, violet and back to red. Only colour can be ordered in a closed circle like this; the observations of the other senses, such as pitch or temperature, run along a line from low to high.

After-images

Staring at a colour intensely for a while and then looking away produces an after-image in the opposite, or complementary, colour on the colour circle. After a minute of looking at a violet-red object, for example, a greenish-blue after-image appears. During prolonged exposure to a bright colour, the cones that register it become desensitised; the negative after-image appears while they recover.

The colour of the after-image is not a physical, material colour. It has a lingering, floating and transparent quality. In the anthroposophical vocabulary that this approach draws on, such a colour is called an etheric colour, a colour that is not attached to any substance. Goethe gave these colours a name of his own: he called them physiological colours, because the eye itself produces them.

Colour and mood in experiments

The effect of colour on mood has been examined in experiments of the following kind. The participants did not know the purpose of the study. Half of the group was asked to paint a certain picture with red paint, the other half the same picture with blue. After fifteen minutes of painting, the group using red was louder and more restless than the group using blue.

Another experiment was carried out in a factory. One room kept its usual colours and the other was painted in soft, warm tones. Before long, the workers in the second room were reported to reach a 15% higher production rate and to take 30% less sick leave than those in the first room.

Such results are hard to separate from other influences, such as the attention the workers received. Still, they point in the same direction as everyday experience. Painters, interior designers and the makers of phenomenological exercises all work with the fact that a room or a sheet of colour changes how a person feels.

Sight among the other senses

Compared with the sense of smell, sight is cool and distant. A smell enters the body and cannot be kept out, while a picture stays over there, in front of the observer. This distance is what makes sight so useful for thinking and for science, and it is also why sight so easily becomes one-sided. Looking at colour with patience, and noticing its effect, turns seeing from pure registration back into experience.