Oticon Alta

The Essential Guide to Hearing Loss

Ed Greenberg, M.Ed.,
Hound Dog Hearing
Assistive Listening Devices
Washington, D.C.

Sound and Speech

The Nature of Sound

Sound waves are vibrating molecules. The molecules are set in motion by vibrating objects. All sounds are produced by objects that vibrate, some only for a fraction of a second.

A plucked guitar string can vibrate rapidly back and forth for several seconds. Every time the string moves to and fro it compresses air molecules, thus pushing out waves of sound like ripples in a pond. Strings that are ''light'' (or skinny) vibrate at higher rates and send out more soundwaves per second, resulting in higher-pitched sounds. Strings that are thicker, and have more mass, vibrate at a slower rate and produce lower-pitched sounds. The right side of the piano has the high-pitched skinny strings. The left side of the piano has the thick, bass notes.

Producing Speech -- Our Unique Vocal Tract

The vocal cords can be thought of as two strips of leather with a gap in the middle, stretched across the top of the trachea (the windpipe). Many muscles control the tension of the vocal cords. When we produce human sounds with our voice, the vocal muscles contract and stretch the vocal cords - creating tension. The gap between the vocal cords narrows. As we exhale air to produce speech, the stream of air passes through the narrow passage, causing the stretched vocal cords to vibrate and produce sound. The process through which speech occurs is similar to blowing air through the reed of a clarinet. The quantity of air passing through the gap determines the loudness. As the quantity of air increases, the vocal product is louder.

Children have shorter vocal cords than adults. As a result, they vibrate more rapidly and produce higher-pitched sounds.

The sounds produced by the vocal cords include an incredible array of utterances and words, produced by the interaction of our tongue, teeth, mouth and lips. In addition, our sounds are made richer and more complex as they pass around and through our vocal tract, including the larynx, throat, sinus cavities, and mouth. The size, shape, and flexibility of these structures vary from individual to individual and give us our unique ''voice personality.''

How We Hear

The Outer Ear -- Catching Sounds

The outer ear has a unique shape that catches waves of sound and funnels them into the ear canal towards the ear drum. The ear canal is about an inch long. The ear drum, also called the tympanic membrane, is the boundary between the outer ear and the middle ear.

The Middle Ear -- Powering Up

The sound waves that reach the eardrum can be pretty faint. Once the sound hits the eardrum, the three tiny bones of the middle ear are also set into motion, and they do an amazing thing. They actually work to help amplify the sound!

Amplification is accomplished in two ways. The first is the ''lever action'' of the three bones. Levers amplify mechanical force. The malleus presses against the eardrum, picks up its vibrations and passes them to the incus. The incus passes them to the stapes. The stapes (looks like a stirrup) terminates in a tiny footplate that fits precisely into the oval window of the cochlea.

The second way sound is amplified in the middle ear has to do with the fact that the surface area of the eardrum is relatively large, whereas the surface area of the oval window is relatively small. The impact of the size ratio between the large membrane (the tympanic membrane) and the small membrane (the oval window) also contributes to amplified sound. In essence, as the sound passes through the outer and middle ear, it becomes louder - and more finely focused as it enters the inner ears oval window. The oval window is the entry way into the inner ear. The inner ear is also called the cochlea.

The Inner Ear -- Converting Mechanical Movement to Electrical Impulse

The mechanical vibrations of the middle ear initiate fluid waves inside the cochlea. The fluids stimulate different areas along the cochlear membrane and the membrane rubs against specialized cells called ''hair cells.'' When the hair cells move, electrical impulses are passed to specific parts of the cochlear nerve and these electrical signal travels along the nerve to the brain. Hearing actually occurs in the brain not in the ear!

Types and Causes of Hearing Loss

Although there are many types of hearing loss, the two most common are 1- Conductive hearing loss and 2- Sensorineural hearing loss. It is possible to have both types at the same time, which is referred to as a ''mixed'' loss.

Conductive hearing loss occurs when sound waves are physically prevented from reaching the inner ear. These problems can usually be corrected through medical or surgical treatment. Common causes of conductive hearing loss include:Perforated Eardrum. The eardrum is like the head of a drum. If it is punctured, it cannot vibrate maximally and sound will not be transferred efficiently from the outer to the middle ear.

Ear wax (cerumen) buildup. Earwax can partially or completely block sound waves from reaching the eardrum. Wax can usually be removed by the audiologist, a nurse, or a doctor.

Fluid in the middle ear is common, particularly in children. There are many types of middle ear infections, in general, they are known as ''otitis media.'' Otitis media can be caused by a cold, the flu, allergies and many other causes. In cases of otitis media, fluid fills the middle ear, preventing the tiny bones from vibrating properly.Sensorineural hearing lossoccurs when the sensory cells of the inner ear (the hair cells) or the auditory nerve are damaged through aging, exposure to loud noise, drug reaction, trauma, genetic factors and other reasons. The most common sensorineural hearing loss is due to gradual exposure to noise over many years.

Decibels (dB)

Loudness is measured in units called decibels. There are many common decibel scales. Sometimes it helps to think of the different decibel scales like the different scales used to measure temperature. We know that zero degrees Fahrenheit is very different from zero degrees Celsius, and they are both different from zero degrees Kelvin! Its the same with decibels.

For a number to have meaning, you must know which scale is being used. The most common decibel scale is the HL scale. Decibels are also difficult to understand because they are not additive. In fact, if you have a 50 decibel sound and you add another 50 dB sound, the result is not 100 dB. It is 53 dB! Decibels are logarithmic, much like the Richter scale used to measure earthquakes.

Perceived Change in Loudness by Decibel Level

This description (below) demonstrates the change in sound pressure level, using decibels, and how the human ear perceives the change in loudness.

1 dB change, not usually perceptible.
3 dB change, usually can be detected.
5 dB change, clearly noticeable.
10 dB change, the sound is perceived as ''twice as loud.''
20 dB change, the sound is perceived as ''four times as loud.''
30 dB change, the sound is perceived as ''eight times as loud.''

Degree of hearing loss

When we speak of hearing loss, we essentially refer to categories of hearing loss. In other words, the degree of hearing loss is based on an average of the hearing loss, as measured across the sounds most important for hearing human speech. If a person has a 45 dB loss in the 4000 Hz range, it means that for him/her to hear a 4000 Hz sound, the sound must be at least 45 dB in loudness. He/she cannot hear sounds below that loudness at that frequency.

Normal hearing

. 0-25 dB.

Mild hearing loss.
Loss of 25-40 dB.
Symptoms:Unable to hear soft sounds. Cannot hear a whispered conversation in a quiet room. Can hear normal conversation in a quiet room, but has difficulty in a noisy environment

Moderate hearing loss. Loss of 41 -70 dB.
Has considerable difficulty hearing normal conversation in a quiet room. If there is background noise, he/she will not be able to hear many of the words.

Severe hearing loss. Loss of 71 - 90 dB. Cannot have a conversation unless the speaker speaks loudly.

Profound hearing loss. Loss of 91 dB or worse. Cannot understand speech even if the person speaks very loudly. Can only hear very loud sounds such as a chainsaw.

Introduction to the Audiogram:
a picture of hearing thresholds

The audiogram can be thought of as a picture of how well we hear. It indicates the softest sounds we hear at different pitches (frequencies). In the audiogram below, look at the left-hand column. As we move down the audiogram, the sounds get louder. In other words, as we move from the top of the audiogram to the bottom, we increase the loudness (measured in decibels, or dB).

Now take a look at the row of figures across the top (125, 250, 500, 1000, etc.). As we move to the right the sounds increase in pitch, like the keys on a piano. We say they are increasing in frequency and they are measured in units called hertz (Hz).

In the audiogram above, the person tested has 10 dB hearing thresholds through about 2000 Hz, at 4000 Hz he has a15 dB threshold, at 8000 Hz, he has a 20 dB threshold. These values are all within the normal range.

The audiogram below represents a moderate hearing loss.

What is the significance of this audiogram? What can it tell us about this person's ability to understand speech? We'll see in the next section.

Hearing Loss and Speech Intelligibility

In the audiogram below, you can see where basic speech sounds lie when engaging in normal conversation.

Two important points about consonants:

  1. Consonants are higher pitched than vowels (they lie more to the right on the chart).
  2. Consonants are softer/quieter than vowels (they lie higher on the chart).

These factors play an important role in our ability to understand speech. For one thing, the majority of people with hearing loss have it in the high frequencies, where the consonants lie. This is especially true of hearing loss due to aging. Many people hear the vowels normally, but cannot hear the consonants. In addition, most consonants are softer and they tend to get drowned out in background noise. This is sometimes apparent when the patient complains that everyone ''mumbles.'' The ''mumble'' is probably an accurate report of their perception! However, it is not usually because everyone is mumbling. Rather, it is usually because the patient can only hear the vowels, and not the consonants! The inability to hear consonants makes it difficult to understand speech because the consonants convey the majority of the speech information! Consonants are far more important to speech intelligibility than are vowels.

Remember, vowels supply power to speech sounds, but consonants give the clarity!

If the patient cannot hear the high pitched consonants, it will indeed sound like everyone is mumbling.

If you or someone you know has ever said, ''I can hear the words, I just can't understand them,'' this is probably why.you hear the powerful vowels, but you dont hear the soft consonants and again, its the consonants that provide clarity!

Consonants also act as breakpoints, separating syllables and words from one another. If we can't hear consonants clearly, words seem to run together and people sound like they are mumbling. And since women and children have higher-pitched voices than men, it seems like they mumble more!

In Summary:

Consonants are more important than vowels in understanding speech.
Consonants are spoken more softly than vowels, and they tend to get drowned out in noisy environments.
Consonants are higher-pitched than vowels and most hearing loss occurs in the higher frequencies.

It's harder for people with hearing loss to hear the consonants in the first place and noisy environments makes it worse. No matter how hard they try, people with hearing loss cannot get it all. The result is fatigue, frustration, and an increasing reluctance to engage in socially frustrating situations.

To illustrate how hearing loss affects speech comprehension, lets superimpose the audiogram of the person with a moderate hearing loss over the speech sounds. The dark area lies below the subject's threshold of hearing. In other words, the darker part of the audiogram is what he can't hear.

As you can see, during normal conversation this person will simply not be able to hear many of the consonants. People will have to speak very loud and this obviously puts a strain on everybody involved.

Communication Tips for Friends and Family

See your hearing healthcare professional. Learn about hearing aids and assistive listening devices (ALDs). Try these products. They work and they make an enormous difference!

In addition..

Decrease the distance
between you and the listener. This is the single most effective way to increase understanding. Moving a little closer can make a big difference.

Don't eat, drink, or chew gum while speaking with someone who has hearing loss.

During conversation, turn off radios, television and other distracting noise sources.

Wait until passing noises subside. While walking down the street, don't ''talk over'' the noise of the passing cement mixer. Wait until it's out of range!

Save important conversation for quiet environments.

Scout out good places. Know which restaurants are quiet and which are noisy. Know which areas of a restaurant are better than others. Avoid the kitchen, cash register, and reception area. Look for restaurants with lots of soft fabrics and upholstery rather than hard-surfaces.

Be sure the listener is ready to hear you. Listeners need a moment to focus - because understanding speech requires more concentration for him than for you! To see why this is so, think of listening to someone with a thick accent - it's much more difficult to understand the first few words if you are unprepared to listen.

For best communication, the speaker and listener should be 3 to 6 feet apart.

Face your communication partner so they can see your lips, your entire face, and hands and body gestures. These all provide valuable cues and can help fill in for sounds theyre not getting. Try to avoid bushy mustaches or other facial hair that obscures the lips. Avoid shadows.

Lighting should be above or in front of you, not from behind you. Don't stand in front of the window while talking to a person with hearing loss. As discussed earlier, they need to observe facial and body gestures. This is particularly important if the listener is further away, as in a classroom.

Face the person with hearing loss and speak directly to them so the volume of your voice doesn't fluctuate. Turning away from someone while talking significantly decreases the volume. Talking into the cupboard while getting the cereal is even worse! Try not to talk while moving around so you offer consistent loudness and constant visual cues.

Speak louder and enunciate clearly, but don't exaggerate sounds and please, don't shout! Exaggerating distorts sounds, and shouting can be very disruptive to the Hard of Hearing (HOH) person for two reasons: First, the HOH person, depending on the degree of hearing loss, may dwell in silence where ambient sounds we take for granted are severely reduced or absent. A sudden loud sound can be startling. Second, there is a reduced listening comfort range between what can be heard and what is uncomfortably loud for people with sensorineural hearing loss.

Rephrase, don't repeat. Vary the words. Some words are more difficult to understand than others and some are more difficult to lipread than others too.

Introduce topics clearly. For example, ''Dad (pause), I want to talk about your trip to Florida'', rather than ''What time is your flight?'' If you are discussing a complex topic, good organization and clear transitions will aid understanding. This is critically important and it relates to the way we listen and absorb information. If we're prepared, it goes more smoothly.

Be sensitive to signs of confusion or uncertainty.

In group conversations, try to have one person speak at a time. The person who is about to speak should provide a subtle visual cue such as a hand gesture. The HOH person can't understand one voice over another and needs to be facing the speaker for maximum clarity. In formal settings, such as book clubs, the leader should indicate who is to speak by pointing and saying his or her name.

Arrange people and furniture to create the best listening environment. In the living room, seat the HOH person away from the kitchen and away from noisy areas. Be sure he is sitting with the noise behind him. In a restaurant, sitting next to the person rather than across from him may be better - if that places you closer. Each situation is different and management strategies need to be flexible.

In summary, do not:

  • Talk rapidly
  • Enunciate poorly and in a quiet voice
  • Speak with food in your mouth
  • Turn away from the listener
  • Speak with your head in the cupboard or from another room or from more than 6 feet away
  • Change topics abruptly, without cues or transitions
  • Use unusual or unfamiliar words
  • Speak when there is significant background noise present
  • Speak in poor lighting

Additional Communication Tips for Teachers

Investigate sound field and FM systems. These technologies are wonderful for the classroom and they make all the difference in the world.

In addition.

Find out what works for the student.
Open communication is essential. Speak to him. Under what circumstances does he/she experience difficulty? You might find if you change a few small things it could make a world of difference.

Keep a clear channel of communication open with the parents. You can learn a lot from each other.

Decrease the distance between you and the HOH student. This is the single most effective way to increase understanding. Moving closer can make a big difference.

Don't eat, drink, or chew gum while speaking.

Wait until passing noises subside. Wait for that plane to pass overhead or for the students to settle down.

Don't talk while children are retrieving material. The HOH student cannot rummage through things and hear you at the same time.

When addressing the HOH student, say his/her name first.

Face the HOH student and speak directly to him so the volume of your voice doesn't fluctuate. Turning away while talking sharply decreases the volume. Talking into the supply cabinet is even worse. Don't talk while writing on the board (this is tough on all students) and try not to talk while moving around so volume level and visual cues don't fluctuate.

Be sensitive to signs of confusion or uncertainty.

In group discussions, arrange seating so the student can see and hear as clearly as possible.

Be aware that the student's hearing ability may fluctuate from day to day (or hour to hour). Fatigue, background sounds that you are unaware of, or health conditions such as ear infection can impede clear hearing.

Be sensitive to student fatigue. Try to understand what this child is going through. It's hard work straining to listen and understand, while trying to fill in the gaps

Announcementsmade over public address systems are particularly difficult to understand. Perhaps someone can ''translate'' for the HOH student.

Speak clearly with good diction.

Give good directions, repeating key elements when necessary or writing them on the board.

Switch to visuals frequently (handouts, overheads, posters, etc.) to provide breaks from, and to supplement listening.

Be aware that overhead projectors are noisy. Don't speak while you are turned to the overhead. Turn off all other unnecessary equipmentand any other potential distractions.

Print new vocabulary on the board.

Be aware of situations when the student will not be able to lipread and prepare beforehand. For example, if you are going to present a slide show with the lights out, some options might be to try for a captioned set of slides, provide him a transcript if one is available, or to seat the student next to you.

Institute a buddy system to always let the HOH student know what is happening, what page they're on, and possibly to take notes for him. The teacher should be considerate of the ''buddy'' and make sure he doesn't miss out on crucial information while helping.

Assignments and homework should be printed on the blackboard or passed out as handouts. Daily and weekly agendas are very helpful in maintaining a strong context.

Be aware that it is impossible to lipread and take notes at the same time.

If you are reading from the blackboard or flipchart, stand next to it so he can lipread and see the printed material easily. Make it easy for the student to focus his attention in one area of the room at a time. Avoid presenting too many visual stimuli at the same time.

Learn the basics of hearing aids, their strengths and their limitations; i.e., under what circumstances he will experience difficulty.

To learn more about these systems and other alternatives, please click here.

NEXT WEEK- Part Two!!!!!!!!!!!

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