Article: Hearing impairment

This article is a physical description of hearing impairment. See Deaf culture for deafness as seen from a cultural model.

A hearing impairment is a decrease in one's ability to hear (i.e. perceive auditory information). It is important to note that the term "hearing-impaired" is considered offensive by many Deaf and hard-of-hearing people, who prefer the two latter terms.

Explanation

While some cases of hearing loss are reversible with medical treatment, many are permanent. Whether temporary or permanent, how severely hearing is compromised is not uniform. In some cases the hearing loss is only mild or moderate, and individuals may not even be aware they are affected. In other cases the degree of deafness is profound and, although vibrations will be sensed, even the sound of a nearby jet engine will not be heard.

Hearing loss can also differ in what pitches (frequencies) are affected. Human beings generally are sensitive to even quiet sounds, as long as the sounds are at certain pitches: ranging from about 125 Hz to 8000 Hz. The "human ear" is best tuned to pick up sounds at the same pitches (frequencies) as speech, from about 500 to 4000 Hz. The blast of a dog whistle is not heard well even by people with normal hearing because it makes a sound that is at a very high frequency, above the normal human range. Some people do not hear well throughout this range, but are "hard of hearing" depending on the pitch of the sound (low frequency hearing loss, high frequency hearing loss, mid-frequency or U-shaped hearing loss).

Hearing impairment comes from different causes. Most commonly, the ear is affected. Conductive hearing losses involve clogging or abnormalities of the outer or middle ear, and only produce mild or moderate impairment, at worst. Hearing loss due to insensitivity of the inner ear, the cochlea, can also be only mild or moderate but can also be much more severe, even causing complete insensitivity to even the loudest sounds (total deafness). Very unusual hearing impairments involve the auditory portions of the brain.

If the hearing loss occurs at a young age, interference with the acquisition of spoken language and social development may occur. Hearing aids and cochlear implants may alleviate some of the problems caused by hearing impairment, but are often insufficient. People who have hearing impairments, especially those who develop a hearing problem later in life, often require support and technical adaptations as part of the rehabilitation process.

Causes

There are five causes of hearing loss: long term exposure to environmental noise, genetic factors, disease processes affecting the ear, medication and physical trauma.

Long term exposure to environmental noise

Populations of people living near airports or freeways are exposed to levels of noise typically in the 65 to 75 dbA range. If lifestyles include significant outdoor or open window conditons, these exposures over time can degrade hearing. The U.S. EPA and various states have set noise standards to protect people from these adverse health risks. The EPA has identified the level of 70 db(A) for 24 hour exposure as the level necessary to protect the public from hearing loss (EPA, 1974).

• Environmental noise-induced hearing loss is the most common form of sensorineural hearing deficit. It was earlier thought that hearing loss occurred in aging and the term presbycusis was coined to describe such effects; however, later research showed that tribal communities not exposed to significant environmental noise did not experience age related degradation of hearing.
• Exposure to high levels of noise (>70 dB(A) or more) for extended periods of time can cause a permanent, sensorineural hearing loss. (See also noise regulation and noise health effects.)
• Noise-Induced Hearing Loss (NIHL) typically begins at 4,000 Hz and spreads downward and upward.
• Earplugs or earmuffs can help to reduce the noise that reaches the ear.
• The louder the noise is, the shorter the safe amount of exposure is. Normally, the safe amount of exposure is reduced by a factor 2 for every additional 3 dB(A). For example, the safe daily exposure amount at 85 dB is 8 hours, while the safe exposure at 91 dB(A) is only 2 hours (National Institute for Occupational Safety and Health, 1998). Sometimes, a factor 2 per 5 dB(A) is used.
• Personal electronic audio devices, such as iPods (iPods often reaching 115 decibels or higher), can produce powerful enough sound to cause significant Noise-Induced Hearing Loss, even though lesser intensities of even 70 dB can also cause hearing loss.

Genetic

Hearing loss can be inherited. Both dominant and recessive genes exist which can cause mild to profound impairment. If a family has a dominant gene for deafness it will persist across generations because it will manifest itself in the offspring even if it is inherited from only one parent. If a family had genetic hearing impairment caused by a recessive gene it will not always be apparent as it will have to be passed onto offspring from both parents.

Dominant and recessive hearing impairment can be syndromic or nonsyndromic. Recent gene mapping has identified dozens of nonsyndromic dominant (DFNA#) and recessive (DFNB#) forms of deafness.

• The most common type of congenital hearing impairment in developed countries is DFNB1, also known as Connexin 26 deafness or GJB2-related deafness.
• The most common dominant syndromic forms of hearing impairment include Stickler syndrome and Waardenburg syndrome.
• The most common recessive syndromic forms of hearing impairment are Pendred syndrome, Large vestibular aqueduct syndrome and Usher syndrome.

Disease or illness

• Measles may result in auditory nerve damage
• Meningitis may damage the auditory nerve or the cochlea
• Autoimmune disease has only recently been recognized as a potential cause for cochlear damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Wegener's granulomatosis is one of the autoimmune conditions that may precipiate hearing loss.
• Mumps (Epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilateral (one ear) or bilateral (both ears).
• Presbyacusis is deafness due to loss of perception to high tones, mainly in the elderly. It is considered by some to be a degenerative process, although there has never been a proven link to aging. (See impact of environmental noise exposure above.)
• Adenoids that do not disappear by adolescence may continue to grow and may obstruct the Eustachian tube, causing conductive hearing impairment and nasal infections that can spread to the middle ear.
• AIDS and ARC patients frequently experience auditory system anomalies.[1]
• HIV (and subsequent opportunistic infections) may directly affect the cochlea and central auditory system.[2]
• Chlamydia may cause hearing loss in newborns to whom the disease has been passed at birth.[3]
• Fetal alcohol syndrome is reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake.[4]
• Premature birth results in sensorineural hearing loss approximately 5% of the time.[5]
• Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf.[6]
• Otosclerosis is a hardening of the stapes (or stirrup) in the middle ear and causes conductive hearing loss.

Medications

See also Ototoxicity

Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the aminoglycosides (main member gentamicin).

Various other medications may reversibly affect hearing. This includes some diuretics, aspirin and NSAIDs, and macrolide antibiotics.

Extremely heavy Vicodin abuse is known to cause hearing impairment. There has been speculation that radio talk show host Rush Limbaugh's hearing loss was at least in part caused by his admitted addiction to narcotic pain killers, in particular Vicodin and OxyContin.

Physical trauma

• There can be damage either to the ear itself or to the brain centers that process the aural information conveyed by the ears.
• People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent.
• Exposure to very loud noise (90 dB or more, such as jet engines at close range) can cause progressive hearing loss. Exposure to a single event of extremely loud noise (such as explosions) can also cause temporary or permanent hearing loss.

Categories of hearing impairment

Hearing loss is categorized by its severity and by the age of onset. Two persons with the same severity of hearing loss will experience it quite differently if it occurs early or late in life. Furthermore, a loss can occur on only one side (unilateral) or on both (bilateral).

Types

There are three major types of hearing loss: neural/sensorineural, conductive, or a combination of both. Treatment depends upon the type of hearing loss that is present.

Sensorineural

Sensorineural hearing loss is caused by damage/malfunction of the inner ear (cochlea, eighth cranial nerve) or auditory brainstem. This can be divided further into a sensory hearing loss (inner ear) or a neural hearing loss (brainstem).

Conductive

Conductive hearing loss is caused by damage/malfunction of the middle or outer ear system (external ear canal, ear drum, or structures in the middle ear space including the malleus, incus and stapes bones).

Combination

Mixed hearing loss is caused by both conductive and sensorineural causes.

Quantification of hearing loss

The severity of hearing loss is measured by the degree of loudness, as measured in decibels, a sound must attain before being detected by an individual. Hearing loss may be ranked as mild, moderate, severe or profound. It is quite common for someone to have more than one degree of hearing loss (i.e. mild sloping to severe). The following list shows the rankings and their corresponding decibel ranges:

• Mild:
  • for adults: between 25 and 40 dB
  • for children: between 15 and 40 dB
• Moderate: between 41 and 55 dB
• Moderately severe: between 56 and 70 dB
• Severe: between 71 and 90 dB
• Profound: 90 dB or greater

The quietest sound you can hear at different frequencies is plotted on an audiogram to reflect your ability to hear at different frequencies. The range of normal human hearing (from the softest audible sound to the loudest comfortable sound) is so great, that the audiogram must be plotted using a logarithmic scale. This, and the different amount of hearing loss at different frequencies, make it virtually impossible to accurately describe the amount of hearing loss in simple terms such as percentages or the rankings, above.

Pre- or postlingual

The age at which the hearing impairment develops is crucial to spoken language acquisition. Post-lingual hearing impairments are far more common than pre-lingual impairments.

Pre-lingual deafness

Main article: Prelingual deafness

Prelingual hearing impairment exists when the impairment is congenital or otherwise acquired before the individual has acquired speech and language, thus rendering the disadvantages more difficult to treat because the child is unable to access audible /spoken communication from the outset. It is important to note that those children born into signing families have no delay in language development and communication. Most pre-lingual hearing impairment is due to an acquired condition, usually either disease or trauma; therefore, families commonly have no prior knowledge of deafness.

Post-lingual hearing impairment

Main article: Post-lingual hearing impairment

Post-lingual hearing impairment where hearing loss is adventitious after the acquisition of speech and language, usually after the age of six. It may develop due to disease, trauma, or as a side-effect of a medicine. Typically, hearing loss is gradual, and often detected by family and friends of the people so affected long before the patients themselves will acknowledge the disability. Common treatments includes hearing aids and learning lip reading. Loneliness and depression can arise as a result of isolation (from the inability to communicate with friends and loved ones) and difficulty in accepting their disability.

Hard-of-hearing

People who are hard of hearing have varying amounts of hearing loss but usually not enough to be considered deaf. Many people who are deaf consider spoken language their primary language and consider themselves "hard of hearing". How one classifies themselves relative to hearing loss or deafness is a very personal decision and reflects much more than just their ability to hear.

The phrase hard of hearing, normally used as an adjective or adverb, can also be used as a noun, referring to people with hearing impairment as the hard of hearing. People who consider themselves culturally deaf, prefer the term "hard of hearing" or "deaf", and perceive "hearing impaired" as an insult.

Hearing impaired persons with partial loss of hearing may find that the quality of their hearing varies from day to day, or from one situation to another or not at all. They may also, to a greater or lesser extent, depend on both hearing-aids and lip-reading. They may perhaps not always be aware of it, but they do admit to it being important to see the speaker's face in conversation.

Many people with hearing loss have better hearing in the lower frequency ranges (low tones), and cannot hear as well or at all in the higher frequencies. Some people may merely find it difficult to differentiate between words that begin with consonantal sounds such as the fricatives or sibilants, z, or th, or the plosives d, t, b, or p. They may be unable to hear thin, high-pitched or metallic noises, such as birds chirping or singing, clocks ticking, etc. Often, they are able to hear and understand men's voices better than women's.

Others will find their condition so much worse if circumstances in their immediate environment affect the way they are able to use their hearing aids, or prevent them from employing their speech reading skills. A room with a high ceiling and a lot of reverberation will affect the sound of a speaker's voice adversely. The position of the listener, too, sitting at a right angle to the speaker at a long seminar table, thus being able to hear only with one, maybe the ineffectual ear, can make a difference. Difficulties can also arise for the listener trying to lip-read, if the speaker is sitting with his back against the light-source and is in this way obscuring his face. A rule of thumb is that bright lighting is to the hearing-impaired what noise is to the hearing; a source of distraction.

The speaker's accent; the topic under discussion, possibly with many unfamiliar words; the softness of his voice; possibly his having a speech impediment; a habit of holding a hand in front of his mouth or turning his face away at times: all these tendencies cause problems to the hard-of-hearing, especially when they have to rely on lip-reading. The rustling of papers, and notebook pages being turned are precisely the noises that will be the first thing hearing-aids pick up.

Noisy situations are especially difficult, because hearing loss not only affects the ability to hear sounds, but also to localize and filter out background noise.

Unilateral hearing loss

People with unilateral hearing loss (single sided deafness/SSD) can hear normally in one ear, but have trouble hearing out of the other ear. Problems with this type of deficit is inability to localize sounds (ie. unable to tell where traffic is coming from) and inability to process out background noise in a noisy environment, such as in a restaurant.

Social impact

Pre-lingual Impairment

In children, hearing loss can lead to social isolation for several reasons. First, the child experiences delayed social development that is in large part tied to delayed language acquisition. It is also directly tied to their inability to pick up auditory social cues. This can result in a deaf person becoming generally irritable. A child who uses sign language, or identifies with the deaf sub-culture does not generally experience this isolation, particularly if he attends a school for the deaf, but may conversely experience isolation from his parents if they do not know sign language. A child who is exclusively or predominantly oral (using speech for communication) can experience social isolation from his or her hearing peers, particularly if no one takes the time to explicitly teach her social skills that other children acquire independently by virtue of having normal hearing. Finally, a child who has a severe impairment and uses some sign language may be rejected by his or her deaf peers, because of an understandable hesitation in abandoning the use of existent verbal and speech-reading skills. Some in the deaf community can view this as a rejection of their own culture and its mores, and therefore will reject the individual preemptively.

Post-Lingual Impairment

Those who lose their hearing later in life, such as in late adolescence or adulthood, face their own challenges. For example, they must adjust to living with the adaptations that make it possible for them to live independently. They may have to adapt to using hearing aids or a cochlear implant, develop speech-reading skills, and/or learn sign language. The affected person may need to use a TTY (teletype), interpreter, or relay service to communicate over the telephone. Loneliness and depression can arise as a result of isolation (from the inability to communicate with friends and loved ones) and difficulty in accepting their disability. The challenge is made greater by the need for those around them to adapt to the person's hearing loss.

Many relationships have suffered because of the anger that occurs when there is general miscommunication between family members. Generally, it's not only the person with a hearing disability that feels isolated, but others around them who feel they are not being "heard" or paid attention to, especially when the hearing loss has been gradual. Many people opt not to choose hearing aids for fear of looking old, since hearing loss is usually associated with old age and that in turn equals ineffectiveness in our society. Family members then feel as if their hearing loss partner doesn't care about them enough to make changes to reduce their disability and make it easier to communicate.

Medical treatments

Approaches

In addition to hearing aids there exist cochlear implants of increasing complexity and effectiveness. These are useful in treating the mild to profound hearing impairment when the onset follows the acquisitions of language and in some cases in children whose hearing loss came before language was acquired. Recent research shows variations in effacacy but some promising studies[7] show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech.

Views of treatments

There is controversy in the culturally deaf community as to whether cochlear implants address wellness concerns, the overall health and psycho-emotional well-being of prelingually deaf children at all.

Gene Therapy

In 2005, there was success of the regrowth of cochlea cells in test subjects by a research team led by Dr. Yehoash Raphael from the University of Michigan.[8]

A team led by Dr. Stefan Heller from Stanford University are pioneering stem cell research in the prospect of regrowth in cochlea cells.[9]

Adaptations to hearing impairment

Many hearing impaired individuals use certain assistive devices in their daily lives. Individuals can communicate by telephone using telecommunications devices for the deaf (TDD) This device looks like a typewriter or word processor and transmits typed text over the telephone. Other names in common use are textphone and minicom. In 2004, mobile textphone devices came onto the market for the first time allowing simultaneous two way text communication. In the U.S., the UK, the Netherlands and many other western countries there are telephone relay services so that a hearing impaired person can communicate with a hearing person via a human translator. Wireless, internet and mobile phone/SMS text messaging are beginning to take over the role of the TDD. Other assistive devices include those that use flashing lights to signal events such as a ringing telephone, a doorbell, or a fire alarm. Video conferencing is also a new technology that permits signed conversations as well as permitting an ASL-English interpreter to voice and sign conversations between a hearing impaired and hearing person, negating the need to use a TTY or computer keyboard.