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Hearing Loss

+What is Hearing Loss?

Three areas to focus on:

Types of hearing loss

Degree of hearing loss

Configuration of hearing loss

+Types of Hearing Loss

Conductive

Sensorineural

Mixed

+Conductive Hearing Loss

Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear.

Conductive hearing loss usually involves a reduction in sound level or the ability to hear faint sounds. This type of hearing loss can often be corrected medically or surgically.

+Conductive Hearing Loss

Possible causes:

Fluid in the middle ear from colds

Ear infection (otitis media)

Allergies (serous otitis media)

Poor eustachian tube function

Perforated eardrum

Benign tumors

Impacted earwax (cerumen)

Infection in the ear canal (external otitis)

Swimmer's Ear (otitis ecxterna)

Presence of a foreign body

+Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL) occurs when there is damage to the inner ear (cochlea), or to the nerve pathways from the inner ear to the brain. Most of the time, SNHL cannot be medically or surgically corrected. This is the most common type of permanent hearing loss.

SNHL reduces the ability to hear faint sounds. Even when speech is loud enough to hear, it may still be unclear or sound muffled.

+Sensorineural Hearing Loss

Some possible causes of SNHL:

Illnesses

Drugs that are toxic to hearing

Hearing loss that runs in the family (genetic or hereditary)

Aging

Head trauma

Malformation of the inner ear

Exposure to loud noise

+Mixed Hearing Loss

Sometimes conductive hearing loss occurs in combination with a sensorineural hearing loss (SNHL). In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.

+Degrees of Hearing Loss

Degree of hearing loss refers to the severity of the loss. The table below shows one of the more commonly used classification systems. The numbers are representative of the patient's hearing loss range in decibels (dB HL).

+Degrees of Hearing Loss

Degree of hearing loss Hearing loss range (dB HL)

Normal –10 to 15

Slight 16 to 25

Mild 26 to 40

Moderate 41 to 55

Moderately severe 56 to 70

Severe 71 to 90

Profound 91+Source: Clark, J. G. (1981). Uses and abuses of hearing loss classification. Asha, 23, 493–500.

+The Audiogram

The audiogram is a graph showing the results of the pure-tone hearing tests. It illustrates the type, degree, and configuration of hearing loss.

The frequency or pitch of the sound is referred to in Hertz (Hz). The intensity or loudness of the sound is measured in decibels (dB). The responses are recorded on a chart called an audiogram that shows intensity levels for each frequency tested.

+The Audiogram: Pitch or Frequency Each vertical line from left to right represents a

pitch, or frequency, in Hertz (Hz). The graph starts with the lowest pitches on the left side and moves to the very highest pitches (frequencies) tested on the right side.

Examples of sounds in everyday life that would be considered “low-frequency” are a bass drum, tuba, and vowel sounds such as “oo” in “who.”

Examples of sounds in everyday life that would be considered “high-frequency” are a bird chirping, a triangle being played, and the consonant sound “s” as in “sun.”

+The Audiogram: Loudness or Intensity Each horizontal line on the audiogram from top to bottom

represents loudness or intensity in units of decibels (dB). Lines at the top of the chart (-10 dB and 0 dB) represent soft sounds. Lines at the bottom of the chart represent very loud sounds.

Examples of sounds in everyday life that would be considered soft are a clock ticking, a voice whispering, and leaves rustling.

Examples of sounds in everyday life that would be considered loud are a lawnmower, a car horn, and a rock concert.

If we were to compare “normal conversational loudness level” (typically 60 dB) with whispering (typically 30 dB), we’d say that whispering is softer than conversation.

+The Audiogram

On the audiogram, the pattern of hearing loss (configuration) and degree are recorded. For example, your hearing might be normal in the low pitches while you have hearing loss in high pitches. In this case, you might hear speech, but it would sound muffled and unclear. If you have hearing loss at all pitches, you might have difficulty hearing any speech.

The audiologist uses a red O to indicate the right ear and a blue X to record the left ear. The farther down the audiogram the Xs and Os appear, the worse the hearing.

+Configuration of Hearing Loss

The configuration, or shape, of the hearing loss refers to the degree and pattern of hearing loss across frequencies (tones), as illustrated in a graph called an audiogram. For example, a hearing loss that only affects the high tones would be described as a high-frequency loss. Its configuration would show good hearing in the low tones and poor hearing in the high tones.

On the other hand, if only the low frequencies are affected, the configuration would show poorer hearing for low tones and better hearing for high tones. Some hearing loss configurations are flat, indicating the same amount of hearing loss for low and high tones.

+Configuration of Hearing Loss

Bilateral versus unilateral. Bilateral means hearing loss in both ears. Unilateral means hearing loss in one ear.

Symmetrical versus asymmetrical. Symmetrical means the degree and configuration of hearing loss are the same in each ear. Asymmetrical means degree and configuration of hearing loss are different in each ear.

Progressive versus sudden hearing loss. Progressive means that hearing loss becomes worse over time. Sudden means hearing loss that happens quickly. Such a hearing loss requires immediate medical attention to determine its cause and treatment.

+Cochlear Implants

A cochlear (koe-klee-er) implant is a device that provides direct electrical stimulation to the auditory (hearing) nerve in the inner ear. Children and adults with a severe to profound hearing loss who cannot be helped with hearing aids may be helped with cochlear implants.

This type of hearing loss is sensorineural, which means there is damage to the tiny hair cells in the part of the inner ear called the cochlea. Because of this damage, sound cannot reach the auditory nerve. With a cochlear implant, the damaged hair cells are bypassed, and the auditory nerve is stimulated directly.

+Cochlear Implants

The cochlear implant does not result in “restored” or “cured” hearing. It does, however, allow for the perception of the sensation of sound.

The benefits from a cochlear implant depend on many factors, such as:

The age of the patient when he or she receives the implant

Whether the hearing loss was present before or after the patient developed language skills

The motivation of the patient and his or her family

+How does a cochlear implant work?

Cochlear implants have external (outside) parts and internal (surgically implanted) parts that work together to allow the user to perceive sound.

+How does a cochlear implant work?

External parts: The external parts include a microphone, a speech processor, and a transmitter. The microphone looks like a behind-the-ear hearing aid. It picks up sounds—just like a hearing aid microphone does—and sends them to the speech processor.

The speech processor may be housed with the microphone behind the ear, or it may be a small box-like unit typically worn in a chest pocket. The speech processor is a computer that analyzes and digitizes the sound signals and sends them to a transmitter worn on the head just behind the ear.

The transmitter sends the coded signals to an implanted receiver just under the skin.

Components of Cochlear Implant

+How does a cochlear implant work?

Internal parts: The internal (implanted) parts include a receiver and electrodes. The receiver is just under the skin behind the ear. The receiver takes the coded electrical signals from the transmitter and delivers them to the array of electrodes that have been surgically inserted in the cochlea. The electrodes stimulate the fibers of the auditory nerve, and sound sensations are perceived.

+Anatomy of a Cochlear Implant

+Cochlear Implant Process

Once a person is referred to the cochlear implant center, more testing is done to determine whether the person is a suitable candidate. This testing usually includes audiologic testing, psychological testing, medical examination, and tests performed by the surgeon.

The process often involves examination using X-rays and MRI (magnetic resonance imaging), as well as counseling. This is done to ensure that the candidate will benefit from a cochlear implant and will have the motivation to participate in the process.

+Cochlear Implant Process Once the decision is made to go ahead, the surgery is

done. Sometimes it involves an overnight stay in the hospital, and sometimes it is done on an outpatient basis.

About 4–6 weeks after surgery, the person returns to the center to be fit with the external parts—the microphone and speech processor—and to activate and program (called mapping) the implant. This initial fitting process is completed over several days and may include additional visits over several months.

The additional visits are needed for activating, adjusting, and programming the various electrodes that have been implanted. Also, as the person develops skill in using the implant, adjustments and reprogramming are required. Usually there are annual visits to the center for checkups once the final programming is made to the speech processor.

+Cochlear Implant Process

Both children and adults receive extensive rehabilitation services from audiologists, speech-language pathologists, teachers, and counselors as they learn to listen, improve speech, use speechreading, and handle communication. They are taught how to use the implant and how to respond to the sounds they are receiving.

For those who have heard before, sounds through the cochlear implant may seem unnatural at first. Those who have never heard before must be taught what the sounds are.

+Best Adult Candidates

Have severe to profound hearing loss in both ears

Have had limited benefit from hearing aids

Have no other medical problems that would make the surgery risky

Have a strong desire to be part of the hearing world and communicate through listening, speaking, and speechreading

Have lost their hearing after speech and language development

+Best Child Candidates Have profound hearing loss in both ears

Have had limited benefit from hearing aids

Are healthy and have no medical conditions that would make the surgery risky

Are involved (when able), along with their parents, in all the steps in the process

Understand (when able), along with their parents, their role in the successful use of cochlear implants

Have (when able), along with their parents, realistic expectations for cochlear implant use

Are willing to be actively involved in their habilitation/rehabilitation

Have support from their educational program to emphasize the development of auditory skills

1-channel

2-channel

4-channel

8-channel

16-channel

Original

Implant simulations by Arthur Boothroyd, based on the work of Robert Shannon.

Total bandwidth is 0 to 6000 Hz, and channel boundaries are logarithmically spaced.

All within-channel frequency resolution is removed. The amplitude envelope in each band is preserved but it is imposed on a band of noise. This band covers the same frequency range as the band of speech from which the envelope was extracted.

This is not “what speech sounds like to an implant user”. The simulation does, however, give an impression of the intelligibility of speech with the kind of dramatic reduction of spectral information produced by a cochlear implant.

For best effect, begin with 1-channel and progress toward the original.

+Cochlear Controversy

A number of members of the deaf community choose to view their deaf status as a subculture of society, in the same sense as a Hispanic person would embrace his or her Hispanic culture.

Deafness is not a handicap per se, but a shared experience which gives the deaf community its unique cultural identity.

To members of this deaf subculture, cochlear implants are considered disrespectful and insulting, since the medical community views deafness as a handicap which must be treated or corrected.

+Cochlear Controversy Another controversy surrounding cochlear

implants and the deaf community is the safety and effectiveness of the procedure. Cochlear implantation involves major surgery in an area of the body filled with delicate nerves which control facial movements. One mistake during surgery could cause long-term facial paralysis.

Cochlear implants can also destroy any remaining healthy auditory nerves, which means a deaf person could lose all remnants of natural hearing which may have helped them adjust to a deaf lifestyle. Cochlear implants require the recipient to undergo significant fine-tuning sessions, and success can vary widely from recipient to recipient.

+Cochlear ControversyThe controversy over cochlear implants

often pits hearing parents against deaf parents when it comes to raising their deaf children in a hearing world.

Many deaf parents would prefer to raise their deaf child in a deaf culture, including the use of sign language and lip reading.

Hearing parents who are not familiar with the deaf community may opt for the cochlear implant surgery to correct their deaf child's perceived handicap.

+Cochlear Controversy

The result may be a deaf child who can partially hear, or a hearing child with a deaf cultural heritage. Either way, the child may face social ostracism from both communities if the parents do not consider the long-term effects of cochlear implant surgery.