Your Hearing—A Gift to Be Treasured
A QUIET evening in the country, away from the noises of civilization, offers a chance to soak in the gentle sounds of the night. A light breeze faintly rustles the leaves. Insects, birds, and animals add their distant calls. What a wonderful sensation to hear such soft sounds! Can you hear them?
The potential of the human hearing system is simply astonishing. Spend half an hour in an anechoic chamber—an acoustically isolated room with surfaces designed to absorb all sound—and your hearing will have slowly ‘turned up the volume’ enough for you to begin to hear unfamiliar sounds originating within your own body. Acoustic scientist F. Alton Everest describes the experience in The Master Handbook of Acoustics. First, your own heartbeat becomes loudly audible. After about an hour in the room, you hear your blood coursing through its vessels. Finally, if you have keen hearing, “your patience is rewarded by a strange hissing sound between the ‘ker-bumps’ of the heart and the slushing of blood. What is it? It is the sound of air particles pounding against your eardrums,” explains Everest. “The eardrum motion resulting from this hissing sound is unbelievably small—only 1/100 of a millionth of a centimeter!” This is “the threshold of hearing,” the lower limit of your ability to detect sound. Greater sensitivity would be of no use to you because weaker sounds would be drowned out by the noise of air-particle movement.
Hearing is made possible through the cooperation of the outer, middle, and inner ear along with the processing and perceptive powers of our nervous system and brain. Sound travels through the air as waves of pressure variations. These waves move our eardrums back and forth, and this motion, in turn, is transferred by the middle ear to the inner ear. There the motion is converted to nerve impulses, which the brain interprets as sound.a
Your Important Outer Ear
The flexible, convoluted outer feature of your ear is called the pinna. The pinna collects sound, but it does far more than that. Have you ever wondered why your ear has all those little folds? Sound waves reflecting off the various surfaces of the pinna are subtly modified according to their angle of arrival. The brain is able to decode these minute variations and determine the position of the sound’s source. The brain does this in addition to comparing the time and intensity of a sound as it enters each of your ears.
To demonstrate this, snap your fingers as you move your hand up and down directly in front of a person who has his eyes closed. Although your fingers remain at the same distance from each of his ears, he will still be able to tell whether the sound comes from above, below, or anywhere in between. In fact, even a person with only one good ear can localize sounds quite well.
Your Middle Ear—A Mechanical Marvel
The primary function of your middle ear is to transfer the movement of your eardrum to the fluid that fills your inner ear. That fluid is much heavier than air. Thus, as is true of a bicycle rider going up a steep hill, a proper ‘gear ratio’ is required to convey the energy as efficiently as possible. In the middle ear, the energy is transferred by three tiny bones, commonly called the hammer, the anvil, and the stirrup because of their shape. This miniature mechanical linkage achieves a ‘gear ratio’ that is nearly perfect for the inner ear. It is calculated that without this, 97 percent of the sound energy would be lost!
There are two delicate muscles attached to the linkage in your middle ear. Within a hundredth of a second of your ear’s exposure to a loud low-frequency sound, these muscles automatically tighten, greatly restricting the movement of the linkage and thus forestalling any possible damage. This reflex is quick enough to shield you from practically all the loud sounds that occur in nature, although not from all those produced by mechanical and electronic equipment. Moreover, the little muscles can only hold this protective posture for up to ten minutes. But this gives you an opportunity to flee from the offending sound. Interestingly, when you talk, your brain sends signals to these muscles to decrease your hearing sensitivity, so that your own voice is not too loud for you.
Your Amazing Inner Ear
The part of your inner ear involved in hearing is contained within the cochlea, named for its snail-shell shape. The casing protecting its delicate mechanism is your body’s hardest bone. Within its labyrinth is found the basilar membrane, one of several tissues dividing the cochlea’s length into channels. Along the basilar membrane lies the organ of Corti, which supports thousands of hair cells—nerve cells that have hairlike ends extending into the fluid that fills the cochlea.
When the movement of the bones of the middle ear vibrates the oval window of the cochlea, it sets up waves in the fluid. These waves move the membranes, just as ripples on a pond move floating leaves up and down. The waves bend the basilar membrane in places corresponding to specific frequencies. Hair cells in those places then brush against the overlying tectorial membrane. This contact triggers the hair cells, and they, in turn, generate impulses and send them to your brain. The more intense the sound, the more hair cells are stimulated and the faster they are stimulated. Thus, the brain perceives a louder sound.
Your Brain and Hearing
Your brain is the most important part of your hearing system. It has the awesome ability to transform the flood of data it receives in the form of nerve impulses into the mental perception of sound. This major role points up the special link between thought and hearing, a connection pursued in the field known as psychoacoustics. For example, your brain enables you to hear one conversation out of many in a crowded room. A microphone does not have this ability, so a tape recording made in the same room might be nearly unintelligible.
The irritation caused by unwanted noises demonstrates another aspect of this link. No matter how low the intensity of a sound may be, if you can hear it at all when you do not want to, it can be irritating. For example, the intensity of sound produced by a dripping faucet is very low. But you may find it extremely objectionable if, in the dead of night, it keeps you awake!
Indeed, our emotions are closely tied to our sense of hearing. Just think of the contagious effect of hearty laughter, or of the warmth engendered by a sincere word of affection or praise. Likewise, a great deal of what we learn intellectually is taken in through our ears.
A Gift to Be Treasured
Many of the fascinating secrets of our hearing remain to be unlocked. But the scientific understanding that has been gained deepens our appreciation for the intelligence and love manifest in it. “In considering the human hearing system in any depth,” writes acoustic researcher F. Alton Everest, “it is difficult to escape the conclusion that its intricate functions and structures indicate some beneficent hand in its design.”
King David of ancient Israel lacked present-day scientific knowledge of the inner workings of our hearing. Still, he contemplated his own body and its many gifts and sang to his Maker: “In a fear-inspiring way I am wonderfully made. Your works are wonderful.” (Psalm 139:14) Scientific research into the marvels and mysteries of the body, including hearing, is adding to the evidence that David was right—we were wonderfully designed by a wise and loving Creator!
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Help for Those With Damaged Hearing
Sustained exposure to loud sound causes permanent hearing damage. Subjecting yourself to excessively loud music or working around noisy equipment without protection is just not worth such a loss. Hearing aids can provide a measure of help to those with impaired hearing, even to some who were born deaf. For many, such devices restore a whole world of experience. After being fitted with hearing aids for the first time, one woman noticed a strange sound outside her kitchen window. “It was the birds!” she exclaims. “I hadn’t heard the birds for years!”
Even without extreme damage, age usually diminishes our ability to detect high-pitched sounds. Unfortunately, this includes the frequencies of the consonants—the sounds often most crucial to understanding speech. Older people, therefore, may find that verbal communication can be disrupted by normal household sounds, such as those produced by running water or by paper being crinkled, since they contain high frequencies that interfere with the consonants. Hearing aids may provide partial relief, but they have their own drawbacks. For one thing, quality hearing aids can be very expensive—completely beyond the reach of the average person in many lands. And in any case, no hearing aid can give you back completely normal hearing. So, what can be done?
Showing consideration goes a long way. Before speaking to someone who has hearing loss, be sure he knows you are about to say something. Try to face the person. This permits him to see your body and lip movements and to get the full strength of the consonants in your words. Move closer to the person, if possible, and speak slowly and clearly; do not shout. Loud sounds are actually painful to many hearing-impaired people. If a statement is not understood, try rephrasing rather than repeating it. Likewise, if your hearing is not what it used to be, you can make it easier for others to communicate with you by moving closer to the one speaking and by being patient. These extra efforts may well result in improved relationships and can help you to stay tuned in to your surroundings.
When addressing a person with hearing loss, face him and speak slowly and clearly
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Organ of Corti