Changes in perception of senses occur as a result of the differences between the two different types of breathing medium – water and air. Let us see how these changes affect divers under water.

Light and Vision
Beginners find it impossible to determine size and distance under water which leads to exaggeration of the size of fish and other objects. When experienced divers have doubts about the extent of something, they always make a comparison by taking it in their hands. This is certainly a good method because muscular senses remain unchanged under water.
According to certain laws in physics, colors lose their brightness with the increase of depth – red disappears below 8 meters, orange – below 10 m, yellow – below 20 m and at greater depth everything looks bluish, greenish or grayish. For instance, if a person hurts himself at a depth of 20 meters, his blood will seem black. Illumination restores the brightness of colors regardless of depth and amateurs are astonished by the diversity of patterns in a world which looked monotonous and dull before.

You may wish to consult the Physics Section for more details on light and vision under water.

Sound and Hearing
Sounds under water, in contrast to those in the air, can be heard at greater distance. For example, the whir of a boat’s engine is heard earlier under water than in the air. If the boat is 15 to 20 meters away, a diver would think that it is above his or her head. Disorientation under water is also a significant problem because the location of the source emitting sound waves is hard to be determined. However, this confusion can be overcome after some practice.

A curious phenomenon, explained with the density of the water and speed of sound waves, was observed by some divers working in an underwater laboratory - “Our voices became funny and unusually loud, shrilling and resonant so that we could not recognize our own voice laughter. Entering the underwater habitat for the first time, everyone burst into laughter as he heard his unpleasant voice. It was like a recording tape set to fast-motion”.

Sometimes, hearing might fail because of outer factors – noise of working engines, noise of air in decompression chambers or that of instruments. However, the most common problem among divers is the middle-ear squeeze.

You may wish to consult the Physics Section for more details on sound and hearing under water.

Equilibrium
Three semicircular canals which control the sense of equilibrium (balance) are located in the inner ear. These canals, filled with fluid, contain ciliated cells and freely-rolling particles of calcium carbonate, called ear sand. When one's head is tilted, gravity forces the particles to shift and irritate the neighboring cilia. Consequently, the ciliated cells, send information to the central nervous system which orientates to the new position of the body. Thus, balance is achieved.

According to Archimedes’ principle, objects appear lighter in water than they are in the air. During their stay under water, divers take no pains in order to keep their position. Because of the reduced weight of the whole body, ciliated cells cannot be irritated by the ear sand to the same extent as they are irritated out of water. That is why they do not send any commands for the change of position. This leads to the state of loose muscles and weightless body which is typical of both divers and astronauts.

With closed eyes, one who is at rest under water quickly loses his or her sense of body position in space. This concerns especially people with neutral buoyancy. Research data show that a swimming diver with his eyes closed determines his body location with an error of 17°± 8°. Orientation also depends on the position of the body – lying on the back, head relaxed backwards, is considered unfavorable.

A diver has to use outer factors which signal his body location. He relies mainly on his eyesight (following the light layer of water above him), air bubbles, which always go up, buoys and other light objects showing the way to the surface.
Divers, suffering from sinusitis, orientate themselves much better for the vertical position of their bodies. This phenomenon can be explained with the difference in pressure that they cannot equalize immediately. They feel pain in the sinuses which suggests an increase of pressure or that they sink.

Sense of Touch
The nervous endings, located under the skin, react to warm and cold, to pain and touch. This sensitivity is of significance because it helps to determine any changes in the surrounding water and to react to them. The sense of touch is reduced and the feeling of pain almost disappears under water. This is due to the fact that water cools the skin and thence – the sensitive cells, and lowers their sensitivity. It is well-known that frozen fingers are insensitive and unable to feel pain. This phenomenon was used by renowned Russian surgeon Pirogoff, who conducted amputation of limbs without anesthetic after freezing them in snow. The reduced sense of pain under water should be taken into consideration because divers might get hurt (without being aware of that) and not take appropriate measures.

Feelings of warm and cold remain unchanged under water. The heat capacity of water is 4 times greater than that of air. Moreover, its thermal conductivity is 25 times greater than that of air. This means that human body loses heat much faster in water than in air. So, abrupt thermal differences can do irretrievable harm to the human organism. That is why divers should trust their “first” and “second shivers”. The former, which are typical when entering water, signal the beginning of cooling. “Second shivers” that are felt later mean danger of overcooling – heat production cannot compensate for heat loss any more! On the other hand, during dive preparation, a diver in a wet suit who has been exposed to the hot sun for a long time might become overheated. These two conditions are named Hypo- and Hyperthermia.

Smell and Taste
The nose in the mask cannot perform its normal function but it can give information on the state of air the diver breathes. Smell of oil, dust or something musty signals that the apparatus was poorly charged by the compressor. Raised water pressure and increased waste of energy are some of the reasons for changes in taste. Students who have had appetite in the first days of diving activities, later become “capricious”. They prefer salads, fruit, yogurt and juices to fish, meat and bakery. These changes are confirmed by divers living in underwater habitats and decompression chambers.

FROM: library.thinkquest