The dream dissolves in music. Suddenly the music is replaced by a raucous buzzing. You pry your eyes open and blearily stare at the clock-radio, then swat it. The buzzing stops. Last night's party has left your mouth tasting like the Russian Army walked through it, and they hadn't changed their socks in weeks. Your teeth feel fuzzy. The only thing that gets you up is the smell of coffee.
The above story illustrates your senses at work. The primary source of information about the world around you you gather through the senses. This type of information gathering is called somatic ("of the body") input.
The brain has no actual, physical contact with the world. It doesn't even have pain nerves, and thus needs no anesthesia when surgically operated upon (of course, the scalp and the skull bones are not likewise blessed and do require anesthesia when the brain is operated upon). Everything the brain knows or reacts to comes to it in only one way: through the senses.
People, like all other sensate beings on Earth, gather their information through their senses. Human senses include the ability to detect electromagnetic waves in the 3800-7600 angstrom range, air waves of 15 to 20,000 beats per second, air-borne and liquid-borne molecules of proper size, quantity and configuration, and to generate nerve impulses triggered by objects impinging on body surfaces with enough force, approximately 1 gram for the fingertips. These senses are better known as sight, hearing, smell, taste, and touch, and are the only methods, as far as we know, of perceiving what exists and happens in the world around us.
The five senses can be divided into two types, noncontact and contact. Noncontact senses, sight, hearing and smell, do not need physical contact with what is being sensed. This does not mean, however, that there is no physical medium being used to get the information to the senses. Sight uses the electromagnetic spectrum, hearing uses waves in the air or water, and smell uses molecules carried in a medium such as air or water (yes, fish not only smell but have a sense of smell as well).
All of these media make physical contact with the appropriate sensing organ. Without such contact, the organ senses nothing. Thus you don't see an apple, you see the electromagnetic oscillations created by light waves striking the apple and reflecting into your eyes. You don't hear a dog barking, you sense the oscillating air waves created by the barking. You don't smell Mom's apple pie, your nose makes contact with molecules the pie released into the air.
Contact senses, touch and taste, require that the organ of sensing make actual physical contact with what they are sensing. There is no medium such as air or water or electromagnetic vibration that can carry the necessary sensory triggers that would allow you to taste or touch something at a distance. Thus you cannot taste the clam dip across the room, nor feel if the iron is hot until you put your finger on it. Without contact there is no sensation.
Sight is one of, if not the most important sense that human beings have. We depend on being able to see things to comprehend the world around us, even to the point of making it a part of the language -- "Let me see that," "I see," "Look, you jerk -- ." Vision gathers far more information in far less time than any of our other senses. The cliche about a picture being worth a thousand words is true in terms of information content. Think how long it takes to describe something as opposed to show a picture of it. No matter how many words you use, some details will be left out that are visible at a glance.
I've heard it said that when people lose their sight their other senses increase to take up the slack. However, in talking to some of my sightless friends, particularly those that lost their sight in their teens, I discovered that the above is not true. What does occur is not an increase in the sensitivity of the other senses, but a new reliance upon them. When they could see, they didn't concentrate on what they heard or smelled or touched; it was easier and more efficient for them to look at it. They heard a sound and looked to see what the sound signified rather than extract from the sound what it meant. When they lost their sight, that primary source of input was gone and they began to concentrate on what they heard or smelled in order to gather information.
Thus, it is clear that sight is a primary source of information about the world. Let's examine how good sight is for the purpose.
Sight involves the eyes, organs mounted on the front of the face. Light waves enter the eye through a lens called the cornea which focuses the light on receptors at the back of the eye called the retina. The receptors release electric nerve impulses that are transmitted to the brain along the optic nerve.
The brain assembles the impulses into what it considers an image. Note that I say "what it considers an image." The picture you see in your mind is a construct made up of many discreet elements, much the way what you see on your television screen is a construct of elements. The resolution is much higher for your eyes than for a television screen, but the principle is the same.
In addition, the eye only sees what it is looking directly at and focused on. You can't see out of the back of your head because the light isn't entering your eyes. There is peripheral vision, but it only provides an idea of what is there, not a clear image. Try it -- look at the spot below and try to read something from the other column: .
Can't be done, can it? You know something is there, but you can't make out the details that allow you to tell just what. Peripheral vision is wonderful for attracting your attention to get you to aim and focus your eyes, but is almost useless for seeing clearly.
Other limitations on sight include what wavelengths of light and at what resolving power you can see. Resolving power is directly related to the apparent size of what you're looking at. If something is too small for your eyes to resolve (which is a function of absolute size, or distance) then you can't see it. For example, the leg hairs on a flea are far too small for the average human eye to resolve. The moons orbiting Mars are certainly large enough, but too far away for the eye to resolve. Thus in either case, they are in effect invisible.
The other major limitation on sight is what wavelengths of light the human eye can detect. As stated above, the human eye sees wavelengths of between 3800 and 7600 angstrom units. This is what we call the visible part of the electromagnetic spectrum.
The electromagnetic spectrum is the full range of waves set up by oscillating electrical charges. Every time an electrical charge oscillates back and forth one time it gives rise to one wave that travels at the speed of light (300,000 kilometers or 186,000 miles per second). Thus a charge oscillating once per second would generate a wavelength of 300,000 km (I will be using metric units in this discussion as they are easier use and the basis of many standard terms coming later). If it oscillated twice the wavelength would be 150,000 km, 100 times 3,000 km, and so on up to millions, billions, septillions and more times per second. The faster the oscillation rate, the shorter the wavelength.
What does all this have to do with sight? The human eye sees in wavelengths. The wavelengths are so short that they are expressed not in meters or millimeters, but in angstroms. One angstrom equals 1/10,000 of a micrometer (1/10,000,000,000 meter). The length in meters of visible light would be 0.0000000000076 kilometers to 0.0000000000038 kilometers, and represents oscillations just under a quadrillion per second.
Compared to the rest of the electromagnetic spectrum visible light is virtually nonexistent. The spectrum ranges from:
Micropulsations as slow as .01 cycle (wavelength of 30,000,000 kilometers, or about halfway from here to Mars at its closest approach),
Radio waves -- 1 to 1 billion cycles (wavelengths from 300,000 to 0.000030 kilometers (30 centimeters)).
Microwaves -- 1 billion to 100 billion cycles (wavelengths 30 to .3 centimeters).
Infrared -- 100 billion to nearly a quadrillion cycles (wavelengths .3 to 0.000076 centimeters)
Visible light -- just under one quadrillion cycles (wavelengths 0.000076 centimeters to 0.000038 centimeters)
Ultraviolet -- one quadrillion to one hundred quadrillion cycles (wavelengths 0.000038 to 0.00001 centimeters)
X-Rays -- 100 quadrillion to 100 quintillion cycles (wavelengths 0.000001 centimeters to 0.000000001 centimeters)
Gamma rays in the 100 quintillion oscillation range (wavelength about 0.000000000000001 kilometers or 38,000 to 76,000 times faster than the human eye can detect).
It's evident that what the human eye can see is definitely not all there is to see. It is clear that the human eye is a very poor detector of the electromagnetic spectrum. It is, however, the only detector of the spectrum humans have.
Hearing is the second most important sense for most humans. Through sound we receive music, spoken words, warnings from barking dogs to air raid sirens, and many other inputs from the world that are not visible.
Hearing is done through the ears, organs mounted on either side of the head. Sound waves enter through the ear canal and strike the ear drum. The vibrations of the ear drum are transferred by small bones and membranes to the inner ear. Here many small hairs (cilia) that are sensitive to certain sound frequencies move, sending nerve impulses to the brain. In the brain the nerve impulses are assembled into a conception of a sound.
Again, as is the case for sight, the brain actually hears nothing. It assembles nerve impulses triggered by air vibrations to arrive at a concept of sound. However, if the nerves are unable to respond to the air vibrations, either because the vibrations are too fast or slow or because of damage to the sensor cilia or nerves, then to the brain there is no sound at all.
The human ear responds to air vibrations from 15 to 20,000 cyclesper second. As with electromagnetic vibrations, this is neither as quickly or slowly as the air can vibrate. The speed of sound is 344.4 meters per second (at 20o C (68o F)). Thus the lowest you can hear, 15 cycles per second, has a wavelength of 22.96 meters. This is basically a groan that you might hear in whalesong. The highest sound, at 20,000 cycles (although for many people the top end is actually 18,000 or lower), has a wavelength of 0.02221 meters.
Compare human hearing with that of bats or dolphins. A bat can hear vibrations of 10,000 to 100,000 cycles per second (it uses from 30,000 to 60,000 for its echolocation sonar). The shortest wavelength for the bat is .003444 meters. The dolphin is even more sensitive to sound vibration. It can emit sounds up to 120,000 cycles per second, and detect vibrations up to 150,000 cycles per second (0.002296 meters). This is nearly ten times more sensitive than the human ear.
Humans can indeed hear a great deal and in fine detail. However, with a sound spectrum as wide as that of the electromagnetic spectrum, again it is clear that humans cannot hear all there is to hear.
The sense of smell is the last of the noncontact senses that you have available. It is also the one sense over which you have the least control, both in terms of what information you receive and what you retrieve from mental storage (see Chapter 6).
Virtually every substance, solid, liquid or gas, releases molecules of distinctive configuration into the air. The human nose contains receptors to which these molecules attach. When a molecule makes contact, the receptor triggers a nerve impulse that travels to the brain. There the brain assembles the nerve impulses and identifies the smell. For example, the molecule of ethyl mercaptan contains four carbon atoms, six hydrogen atoms, and one sulfur atom. When this molecule comes in contact with nasal receptors the brain assembles and identifies the smell as a combination of rotting cabbage, garlic, onions and sewer gas.
The human nose is quite sensitive. Some 17,000 smells have been classified so far. You can detect a concentration as low as 2 parts per quadrillion (a compound called vanillaldehyde). This means you would be able to smell vanillaldehyde if an ounce of it was diffused in a sealed room 360 X 300 X 45 feet (4,860,000 cubic feet (0.0033 cubic miles)).
It appears that your sense of smell is superb and there can be no caveats about it, unlike sight and hearing. That is not true. As sensitive as your nose is, the bloodhound dog's is a million times more sensitive. It can detect vanillaldehyde if an ounce of it is diffused in a sealed room containing 33 cubic miles of air. Again, you can't possible smell all there is to smell.
The two human senses that require actual contact with that being sensed are touch and taste.
The brain assembles the sense of touch from nerve impulses. The impulses are triggered by anything that impinges with sufficient forceagainst one or more nerve endings on the surface of or inside the body. Here is an experiment to demonstrate this. Rub your index finger very lightly along the top of your bottom row of teeth. Note that you feel the separations and ridges of your teeth. Now take a pencil and rub it along your teeth. Now you feel nothing. Now take your finger and press harder as you rub your teeth. Now you feel your teeth with your finger, but also the pressure of the rubbing through your gums.
What has happened? The first step, lightly rubbing with your finger, triggered the nerves in your finger and allowed you to feel your teeth. The second step did not allow any nerve endings to be triggered and thus you felt nothing (you did, of course, feel the pencil but did not feel your teeth). The third step triggered nerves not only in the tip of your finger but in your gums through the pressure of your teeth on your gums. Thus you felt something in both places. Note that in no instance did your teeth feel anything -- they have no nerve endings and thus can no more feel anything than you can see through your nose.
The sense of touch also operates inside the body. Heartburn is gas in the stomach and intestinal tract that expands and presses on the tissues and organs around them. Headaches are caused by air or fluid pressure (migraines are caused by expanded blood vessels in the head). Again, touch is having a material object impinging on nerves and triggering impulses that tell the brain the something is there.
The sense of touch is quite sensitive, depending on where on your body the nerves are located. The thinnest skin on your body is your eyelids and you can feel a loose eyelash. The thickest skin is on the soles of your feet and, depending on what kind of footwear you use and how long you've used it, you can run through a jungle and not feel a thing (never wore shoes). You can feel the delicate tickle of a hair resting on your skin, or the blinding pain of electric shock.
An interesting fact about the sense of touch is that it actually takes place in the brain. It is true that in the majority of instances, without a physical contact triggering a nerve impulse to tell the brain that a touch has taken place, it doesn't know one has. However, the brain can imagine a touch that has not taken place, or ignore one that has.
A standard practice in law, politics, war and religion has been the use of torture as a form of coercion. So standard was torture in Roman law that a slave could not give testimony in court unless he or she was first tortured to ensure truthfulness (the torture could be as simple as lightly pressing a dull knife against the arm, but torture it was considered). One thing that torture masters (a legitimate and often highly regarded profession for centuries) discovered was that if the pain was too great or too continuous the brain turned off the sense of touch. From then on the victim no longer felt anything and the torture was ineffective. A good torture master learned at what point the victim became numb and earned his pay by keeping the pain at the maximum without allowing the victim to become numb.
The brain also imagines touches that aren't taking place. Such touches are called psychosomatic (mind over body). A common complaint of amputees is that they can still feel the amputated part -- the missing foot (hand, leg, etc.) hurts or itches and can't be rubbed or scratched. There are reports that practitioners of certain Eastern religions and cults are capable of total control over their sense of touch. They are fakirs, firewalkers and esthetes who, in an attempt to achieve nirvana or a oneness with the universe, mortify the flesh with no pain or ill effects. Nonpractitioners can only accept their word that they feel little or nothing from lying on a bed of nails or pushing long pins through their tongues and cheeks, but they show no sign of pain.
Obviously, if the brain can be fooled or controlled then the sense of touch is unreliable as an objective input of information. It is useful and even vital to avoid harm (pain is a warning of a physical danger to the body), but the unreliability and the necessity to make physical contact makes it a poor source of total information about the world.
The sense of taste is arguably the least useful human sense. It, like touch, requires physical contact with what is being sensed. In addition, it requires that you touch what is being sensed with your tongue. For many people, there are things that they refuse to put in their mouths (slugs, excrement, bugs, etc.) which limits taste's value in discovering all there is to know about some things.
The tongue is covered with sensors called taste buds. Taste buds release nerve impulses to the brain when molecules of certain types make contact with them. The human tongue is capable of detecting four different types of flavor: sweet, sour, salty and bitter. (In constrast, some animals cannot taste these four. Cats, for example, cannot taste anything sweet.) Everything you taste, from chocolate cake to garlic bread, is a combination of these four flavors in varying proportions.
As for other senses, the lack of range of possible information that can be gathered because of the limitations on input makes taste incomplete. The four tastes are like the three primary colors used for sight. Combining the primary colors produces all the colors a human can see. However, they leave out entirely anything in the electromagnetic spectrum outside the visible band. The same applies to the four primary tastes.
Such sensory inputs are direct impressions. They enter the brain directly and are responded to without conscious thought or manipulation. They are the ones that make you say "ouch" when you burn yourself and "ah" when the pain goes away.
However, when one notices the limits on each sense, one cannot fail to realize that it is impossible for any person to perceive all there is to perceive. The electromagnetic spectrum extends far above into the ultraviolet and radiation and below into the infrared and radio than the narrow visible light range that humans can see. Many animals can hear and smell far better than humans. Touch requires an actual physical presence with the object being touched.
Mao Tse-Tung said, "All genuine knowledge originates in direct experience." This means that if you don't sense it yourself, it doesn't exist. Thus there are no black cats in coal cellars, no germs or bacteria, no moons around Mars, and no one you haven't met exists.
There are very few people who would believe any of the above. Nonetheless, there is a problem. If you haven't sensed it, how could you possibly know about germs, bacteria, Martian moons and other people? The answer is in the next chapter -- extrasomatic inputs of information.
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