The Amazing Ability of Hearing
IF YOU possess good hearing, you have something truly precious. Just think! You can listen to the melodious song of a bird, the ripple of a brook, the voice of a loved one. Through your ears you can receive lifesaving messages, too—perhaps from an automobile horn, a siren or a fire alarm.
Yet, have you really given much thought to your amazing sense of hearing? And what about that possessed by other creatures? Even a brief investigation can be intriguing.
How Are You Able to Hear?
A glance at the accompanying illustration shows that your ear is much more than that trumpetlike organ on the side of your head. That part is merely the auricle. It catches sound waves and sends them inward, along the external auditory canal. In it are tiny hairs and wax-producing glands. Their purpose? To prevent dust, insects, and so forth, from going deeper and causing damage.
When sound waves reach the end of the canal, they strike your eardrum, composed of thin, taut tissue. Its resulting vibrations are amplified and transmitted in your middle ear by three minute bones, the auditory ossicles. They are commonly called the hammer, anvil and stirrup because of their shapes. The stirrup “taps” the membrane of the “oval window,” transmitting the vibrations to your fluid-filled inner ear. Sound waves also enter the inner ear through the “round window,” below the “oval window.” Some waves even travel through your skull bones into the inner ear.
Above the inner ear’s central vestibule are the semicircular canals. Movements of fluid within them enable you to maintain physical balance. However, hearing is associated with the cochlea. Sound waves passing through fluid set in motion the cochlea’s basilar membrane. In turn, its movement causes vibration of the hair cells making up the organ of Corti. This motion stimulates the nerves attached to the hair cells. Finally these nerves, through the auditory nerve, send messages as electrical impulses to your brain’s hearing center. All of this is well known, but just how a person can understand such signals continues to baffle men of science.
A Word About What You Hear
You cannot hear every sound that surrounds you, and that is a good thing. As a babe in arms, your auditory range may have run from 15 to 30,000 cycles, or vibrations, a second. But say that it was very far below 15 cycles. Why, then you would hear your own heartbeats, even your bone and muscle movements!
Though it has certain limitations, your hearing range is astounding. While individuals differ, in general the loudest sound that one can tolerate is 2,000,000,000,000 times as great as the least perceptible sound! Indeed, the human ear has the maximum sensitivity practical for its needs.
As the years pass, of course, imperfect humans experience progressive loss of hearing ability. Among other things, this is because tissues of the inner ear lose their elasticity. The upper level of the auditory range reportedly drops from 30,000 cycles when one is a baby to around 4,000 cycles by the time one is eighty. Nevertheless, even that is enough for normal conversation.
Truly a Masterwork!
Your ears have built-in protection against extremely loud noises. Of course, a sudden nearby explosion can result in excessive vibrations that could cause irreparable damage to your intricate hearing apparatus. But if a very loud sound develops gradually, quick-acting muscles can ‘turn down the volume.’ The eardrum’s membrane is tightened to reduce its vibrations, and middle-ear muscles twist the auditory ossicles. Thus the stirrup does not transmit such great vibrations through the “oval window” into the inner ear.
Protection also is afforded by the Eustachian tube, running from the nasal cavity to the middle ear. This passageway carries air and equalizes the pressure inside your eardrum with that outside. Here, then, is a safeguard against the breaking of your eardrum due to a great change in external air pressure.
Think, too, about the sounds you hear. In an amazing way, you distinguish between the rumble of thunder and the clatter of wagon wheels, the footsteps of a person and the hoofbeats of a horse, even if you cannot see their source. Moreover, usually both ears can be ‘tuned in’ on sounds. Perhaps you dropped a coin and did not see where it rolled. Yet, you heard it hit the floor, possibly bouncing a time or two. Then you listened as it rolled and struck a chair. Finally, you heard the coin flop over and reverberate before coming to rest. Both ears help you to locate the spot.
Not without good reason, it has been said of the human ear: “If an engineer were to duplicate its function, he would have to compress into approximately one cubic inch a sound system that included an impedance matcher, a wide-range mechanical analyzer, a mobile relay-and-amplification unit, a multichannel transducer to convert mechanical energy to electrical energy, a system to maintain a delicate hydraulic balance, and an internal two-way communications system. Even if he could perform this miracle of miniaturization, he probably could not hope to match the ear’s performance.”—Sound and Hearing, by S. S. Stevens, Fred Warshofsky and the editors of Life, page 38.
Yes, the human ear truly is a masterwork. How well it demonstrates the wisdom of Jehovah God, the incomparable Maker of the hearing ear!—Prov. 20:12.
Hearing in the Animal World
You have a right to be impressed with the wonder of human hearing. But what about that of other creatures? Well, people can see the external ears of dogs, cats, horses and monkeys, and they know that such animals respond to sounds. Also, though birds lack external ears, most persons are well aware that these creatures can hear. As a matter of fact, a bird’s auditory range is about the same as man’s. What about snakes? Can they hear?
Some naturalists contend that snakes cannot hear. Actually, however, recent findings show that these animals have an auditory mechanism and can hear fairly well. For instance, researchers Peter H. Hartline and Howard W. Campbell found that not only substrate vibrations but also airborne sounds evoked electrical responses in species of three snake families. Concerning a boa constrictor, they wrote: “If a brain response is accepted as indicative of hearing, these snakes can hear airborne sound.”—Science, March 14, 1969, Vol. 163, No. 3872, page 1222.
The Bible implies that the cobra can “listen to the voice of charmers.” (Ps. 58:4, 5) In this regard, the New York Times of January 10, 1954, stated: “Dr. David I. Macht, research pharmacologist of the Mount Sinai Hospital in Baltimore, is one of the world’s leading authorities on cobra snake venom. . . . Dr. Macht reported that in working with cobras and cobra venom he became acquainted with a number of Hindu physicians, well educated, and from different parts of India. All agreed that cobras respond to some musical tones, from musical pipes or fifes. Some forms of music excite the animals more than other forms, the physicians reported. Indian children, playing in the dark in the countryside, are even warned not to sing lest their sounds attract cobras, he said. Dr. Macht commented that Shakespeare, who repeatedly referred to serpents as deaf . . . merely repeated a common misunderstanding. On the other hand, Dr. Macht said, the psalmist was right who implied conversely, in Psalm 58, Verse 5, that serpents can hear: . . . Contrary to the claims of some naturalists, Dr. Macht said, snakes are ‘charmed’ by sounds, not by movements of the charmer. Revise the textbooks, the physicians recommended.”
What About Insects?
Some researchers have concluded that not all insects can hear. Yet, many of these little creatures have remarkable hearing ability. Some respond to sounds below man’s auditory range. Others can detect those over two octaves higher than any that humans can perceive.
Insect auditory equipment varies and often turns up in unusual places. Eardrums of short-horned grasshoppers are on the sides of their abdomens. The male attracts a lady grasshopper by rubbing the edges of his front wings with spines attached to his back legs. This is ‘music to the ears’ of the female that hears it and decides to become his mate.
Katydids and crickets have “ears,” too. Where? Just below what you might term the “knees” on their front legs. Of course, these are only tiny openings. But all the female katydid must do to pick up the male’s mating sound is to move her legs in the direction of the call!
The Marvel of Echolocation
Some creatures employ the sense of hearing in quite an extraordinary way. They are equipped for echolocation. These animals emit high-frequency sounds and are guided, by listening and responding to rapidly returning echoes as the sounds are reflected by objects. For instance, bottle-nosed dolphins use this method to avoid underwater obstacles.
Among echolocators is a well-known flying mammal—the bat. If you were to release a bat in a completely dark room, it could-fly about without hitting the walls or other objects. This is because the animals emit sound pulses of high frequency; as the sounds strike obstacles, they listen for the echoes. Why, they sometimes send out over 200 pulses a second! By interpreting the messages resulting from these echoes, the creature-charts a safe course.
The bat also uses its astounding guidance system to locate the insects on which it dines. But just how it tells the difference between echoes reflected by obstacles and those returning from potential meals remains a mystery to man. For that matter, certain bats catch their prey right on the obstacle, a leaf.
Another remarkable factor is that the bat does not hear the sounds it emits. Every time one is sent out, ear-muscle contractions ‘turn off the sound’ so that only the echo is heard. Furthermore, each bat may possess and follow its own pattern of sound because there is not mass confusion when hundreds of these creatures flock together.
What a system of sound emission and hearing the Creator has given the bat! It has been said: “Scientists estimate that, ounce for ounce and watt for watt, the bat’s sonar is a billion times more sensitive and efficient than any radar or sonar device contrived by man.”—James Poling, in Marvels & Mysteries of Our Animal World.
Protect Your Hearing Ability
Whether you look at the animals or consider yourself, doubtless you will admit that hearing ability truly is amazing. And surely you will want to care for and protect your hearing apparatus.
Your ears are being assailed by many unwanted sounds in this modern world. Noise pollution has become quite a problem in many places. If you must work around excessively loud machinery, for example, the use of earplugs may be advisable. They may protect you against ear injury and hearing loss.
If you now are a tobacco user, another way to protect your hearing is to stop using tobacco. The nicotine in tobacco causes constriction of inner-ear arteries. This, in turn, reduces blood flow and consequently the flow of nourishment that the inner ear needs in order to play its vital role in your life.
Never probe in your ears with objects such as hairpins or matchsticks. If you break the skin in this way, infection may result.
Do you have your ears examined from time to time? Well, having periodic ear examinations would not be amiss. It certainly pays to protect your amazing ability of hearing.
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THE HUMAN EAR