Sense of balance – orientation, uprightness and proportion

The sense of balance is used to orient oneself in the world. Observations made with this sense let you know what is up and down, left and right, in front and behind, above and below. The sense of balance perceives the smallest changes in your vertical position. In Rudolf Steiner's scheme of twelve senses it is the fourth of the senses directed at the own body, after touch, the sense of life and the sense of movement.

A dynamic equilibrium

The body has a dynamic equilibrium. Balance is maintained by very small adjustments in muscle tension in muscles all over the body. Every time you stand up you have to rediscover your balance, by using this sense.

Standing still is therefore never really still. Anyone who stands on one leg with closed eyes feels the ankle, knee and hip correcting all the time, and the body sways a little around its point of balance. Even with both feet on the ground, the body rocks slightly back and forth. These movements are too small to be seen from a distance, but they show that uprightness is an achievement, renewed from moment to moment.

Young children show how much practice this takes. A baby first learns to hold its head up, then to sit, then to stand while holding on, and finally to walk freely, usually around the end of the first year. Each step is a new conquest of gravity. Walking itself has been described as a controlled fall: the body tips forward and catches itself with the next step.

The eyes and the organ of balance

The organ of balance is not the only organ used to maintain balance. The eyes are at least as important to orient oneself in the surroundings. They see vertical and horizontal objects which confirm the information given by the organ of balance. Try walking in a room where everything is at odd angles. Balance could be so distorted that the surface of the water in a bucket (which is in fact always horizontal) would appear to be sloping downhill.

The sense of movement in the muscles and joints is the third source. Pressure under the soles of the feet, tension in the calf muscles and the angle of the ankles tell the brain how the body stands on the ground. When the three sources agree, balance feels effortless. When they contradict each other, for instance on a ship where the eyes see a steady cabin while the inner ear feels the rolling of the waves, many people become seasick. The same happens to some passengers reading in a moving car.

The share of the eyes is easy to test. Standing on one leg with open eyes is simple for most people; with closed eyes the swaying increases at once, and many have to put the other foot down within seconds. Without the confirmation of the eyes, the inner ear and the muscles have to do all the work.

The organ of balance in the inner ear

The organ of balance is situated in the petrous part of the temporal bone, next to the cochlea, the organ of hearing. It is made up of three semicircular canals, which are perpendicular to each other, and two small sacs, the utricle (utriculus) and the saccule (sacculus).

The three semicircular canals are filled with a fluid that moves with every movement of the head, thus registering changes in direction. Each canal widens at one end into a small chamber containing a gelatinous cap over sensory hair cells. When the head turns, the fluid lags behind for a moment and bends the cap, and the hair cells register the rotation. Because the canals are at right angles to each other, they can perceive movement in every direction.

The utricle and saccule perceive linear position and linear displacement. Each contains a patch of sensory hair cells covered by a gel-like layer in which small crystals of calcium carbonate are embedded, the otoliths. The weight of these crystals makes the gel shift whenever the head is tilted or accelerated. In the utricle this sensory patch lies roughly horizontal; it detects changes in horizontal acceleration, such as when a car accelerates or pulls over, and the tilting of the head. In the saccule the patch stands roughly vertical; it responds to vertical acceleration or deceleration, such as in a lift. At constant speed, the pressure on the sensory cells does not change, so it is not noticed.

This is why a smooth ride in a train or aeroplane is hardly felt at all, while starting, braking and turning are felt clearly. The organ of balance registers changes, not a steady state.

Spinning and dizziness

When someone spins around a few times, the fluid in the semicircular canals is gradually set in motion along with the head. When the spinning stops, the fluid keeps moving for a moment. The canals then report a rotation that is no longer there. The eyes react with jerking movements, called nystagmus, and the surroundings seem to turn. Standing up straight becomes difficult until the fluid has come to rest. Ice skaters and dancers who make pirouettes learn to limit this effect, partly by fixing their gaze on one point for as long as possible during each turn.

Balance and the joints

Together, the three-dimensional planes in the organ of balance cover all the degrees of movement in the joints. According to this description, ankle, knee, elbows, shoulder and jaws move in the same planes as the organ of balance. The observation connects the small organ in the head with the movements of the whole body: the three directions of space that the inner ear perceives are the same directions in which the limbs bend and turn.

Observing the surroundings with the sense of balance

When other objects are observed, the organ of balance is used in different ways. First, to determine the position of the object in the surroundings, taking the horizon as orientation. Secondly, to observe whether something is standing straight up, or leaning, and whether something is actually horizontal or only seems to be. It is possible to detect how far something is out of true. Finally, using the organ of balance one can detect whether something is out of proportion, e.g. whether length is in proportion with height.

The phenomenological approach makes use of this when looking at trees and animals. A tree trunk that rises almost, but not quite, vertically gives an impression of tension; the eye seeks the position where it would be in rest. The low, bending branches of a mature beech make the same kind of impression. Proportions of animals can be looked at in the same way. A giraffe is extremely tall in relation to its length, a dachshund extremely long in relation to its height, and between them lie countless intermediate forms. On the page about ungulates, such proportions of the body return in the description of horse, pig and cow.

Balance in animals

An organ of balance is found throughout the animal kingdom. Fish have an inner ear with semicircular canals and otoliths much like the human one, although they have no outer or middle ear. Many invertebrates, such as jellyfish, crabs and snails, have small fluid-filled vesicles with a heavy grain inside, called statocysts, that tell them which way is down. The principle is the same everywhere: a weight that presses on sensory cells in the direction of gravity.

Mammals differ greatly in how much their way of life asks of this sense. Cattle and pigs stand firmly on four legs and rarely need to catch themselves. Squirrels and monkeys leap between branches and land with precision. The domestic cat is famous for its righting reflex: dropped upside down, it turns its head first, then the front of its body and then the hind part, and lands on its feet. The page on dog and cat describes more of the cat's agility. Birds combine the organ of balance with the eyes in flight, and a hovering kestrel keeps its head almost motionless in the air while its body and wings adjust to every gust.

The human being takes a special position here. With only two feet on the ground and the heavy head on top, the body is far less stable than that of a four-legged animal. Standing upright therefore asks more of balance than it does for any four-legged mammal, and the loss of balance in old age, when the organs and muscles work less well, is correspondingly noticeable.

Balance in the tradition of the twelve senses

In the anthroposophical description, balance is more than a mechanical sense. It is connected with uprightness, and uprightness is regarded as a characteristic of the human being: people stand and walk on two legs with the head held above the body, while most mammals carry the body horizontally. Balance is also said to give a sense of rest and of being centred, a point from which the world can be observed. In this tradition the sense of balance is often paired with the sense of hearing, one of the senses directed at other people; the two organs sit side by side in the inner ear. The pairing is part of the tradition's description, not a physiological finding, but the anatomical neighbourhood is real.

The page on the sense of hearing describes the organ that shares the inner ear with the organ of balance.