How can noise be hazardous to your hearing? What causes hearing loss? What can we do to protect ourselves from noise pollution?

Insights

Have you ever heard a ringing in your ears after a loud concert? Did sounds seem muffled? These could be early signs of permanent hearing loss. Constant or even occasional loud noises can damage your hearing beyond repair. More than 35 percent of the 28 million cases of hearing loss in the United States are caused, at least in part, by exposure to hazardous noises.

Hazardous noise can be anything from loud music to the sounds of a lawn mower. To find out how hazardous a sound is, we measure its loudness in decibels, which tell us its power or intensity. The decibel scale is logarithmic-each 10-dB increase is a factor of 10.

The normal human ear can hear sounds down to 0 dB. The roar of a rocket lifting off registers over 140 dB. Experts consider noise levels above 85 dB hazardous, particularly when you're exposed to them for long periods. The louder the noise, the less time it takes to damage your hearing. Many rock concerts are 110 dB or more. If you attend often, you can damage your hearing before you know you are in danger.

The ear has three parts-the outer, the inner, and the middle ears. The outer ear includes the visible part outside our head and the ear canal, which ends at the eardrum. The middle ear contains three tiny bones called ossicles. The inner ear contains the cochlea, housing thousands of hair cells and nerve endings.
When sound waves travel down the ear canal and strike the eardrum, it vibrates. This causes the ossicles to vibrate. The sound is then transmitted to the inner ear. Vibrations set the fluid within the cochlea in motion, stimulating the hair cells. The movement of the hair cells stimulates the auditory nerve endings, which send the sound pattern to the part of the brain that interprets it.

Hearing problems in the outer and middle ears can cause conductive hearing loss. An example is otitis media, fluid in the middle ear caused by infection. These problems can often be corrected with medicine or surgery. Sensori-neural hearing loss is usually permanent and is caused by damage to hair cells in the inner ear. When hair cells or auditory nerves are destroyed, they cannot be repaired. Loud and persistent sounds can damage hair cells and cause permanent hearing loss and tinnitus.

Next time you listen to music, keep the volume low and rest your ears often. Use earplugs at concerts. Remember, once your hearing is damaged by loud noise, it's gone forever!

Connections

1. Name ten jobs that involve loud noise. How could you protect your hearing at these jobs?
2. How would society and life as we know it change if no one could hear?

Key Words

cochlea spiral-shaped cavity of the inner ear that contains hair cells and nerve endings
conductive hearing loss hearing loss caused by a problem in the outer and middle ears
decibel logarithmic system of rating where the larger the number, the louder the sound
eardrum membrane forming a tight seal between the outer ear and middle ear
ossicles the three bones-malleus, incus, and stapes-that send sound from the eardrum to the inner ear
sensorineural hearing hearing loss caused by a problem in the inner ear, along the auditory nerve, or in the brain
tinnitus ringing, roaring, or other sensation of noise in the ears

Resources

1. Bahadori, R.S. & Bohne, B.A. (1993, Apr) Adverse effects of noise on hearing. American Family Physician, p. 1219.
2. Jaret, P. (1990, July-Aug) The rock & roll syndrome. Health, pp. 50-57.
3. Kittredge, M. (1990) The senses. New York: Chelsea House Publishers.
4. Vernick, D. (1993) The hearing loss handbook. New York: Consumers Union.

Additional resources

1. Boston Broadcasters: The ear. Videotape. MTI: (800) 777-8100.
2. Centron Educational Films: Ears: Have you heard the latest? Videotape. Simon & Schuster Communi-cations: (212) 698-7000.
3. Pyramid Film & Video: I am Joe's ear. Film and videotape. (800) 421-2304.
4. Queue Inc.: Learning all about heat & sound. CD-ROM for Macintosh or MS-DOS. (800) 336-2481.
5. 3M Learning Software: What's the secret? CD-ROMs for Macintosh or Windows. (800) 219-9022.

Additional sources of information

1. American Speech-Language-Hearing Association
   10801 Rockville Pike
   Rockville, MD 20852
   (800) 638-8255
2. Hearing Education and Awareness for Rockers
   PO Box 460847
   San Francisco, CA 94146
   (415) 773-9590

Main Activity

Materials

• objects to make noise with, such as blocks, stones, coins, a glass, empty can, or pen
  
• scarf or handkerchief for a blindfold
  
• earplugs (available at most hardware, drug, music, or sporting- goods stores)

1. Choose a classmate to sit blindfolded in the middle of a circle of students seated at various points around the room. Have this student place an earplug in one ear.
   
2. Silently point to a student in the surrounding circle, who then makes a sound with one of the objects you've gathered. For instance, that person can use the object to clap, tap, click, snap, or rattle.
   
3. Ask the blindfolded student to point back in the correct direction of the sound and identify it.
   
4. Repeat this step with five other students in the circle, each of whom makes different sounds. Record how often the blindfolded student identifies the correct location and sound.
   
5. Ask the blindfolded student to unplug her or his ear. Repeat the process. Is she or he better able to identify the location and source of the sounds?
   
6. Select other students in the class and repeat the experiment. Are some students more accurate in distinguishing sounds and locations than others? Why do you think this is so?

Questions
1. What sounds were easiest to identify? Which were hardest? Does this tell you anything about the way we hear and the sounds we expect to hear?
2. What are some things you can do to improve your hearing or listening ability?

Get a stopwatch and hold it close to a classmate's ear. Then move it out from the ear until your partner can no longer hear the sound. Measure and record this distance. Repeat for the other ear. Is the distance the same?

Watch your favorite TV show with the sound off. How much of the plot or dialogue did you understand? What did you find yourself paying attention to that you might not have noticed normally?

Bats and dolphins use ultrasonic sound waves to "see" with sound. Conduct research on how they navigate and sense the world by echo. Find out how insects, birds, reptiles, and fish hear. Do they have ears? What kind of ossicles do they have?

Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.