Noise Exposure:
Noise-induced hearing loss is the second most common form of sensorineural
hearing deficit, after presbycusis (age-related hearing loss).
Exposure to high levels of noise (>85 dB or more) for extended periods
of time can cause a permanent, sensorineural hearing loss.
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. For
example, the safe exposure amount at 85 dB is 8 hours, while the safe
exposure at 90 dB is only 2 hours, 31 minutes (National Institute for
Occupational Safety and Health, 1998).
Portable electronic devices, like iPods can produce powerful enough sound
to cause significant Noise-Induced Hearing Loss.
Categories of hearing impairment:
Hearing loss is catagorized by its severity and by its age of onset. Two
persons with the same severity of hearing loss will experience it quite
differntly if it occurs early or late in life. Furthermore, a loss can
occur on only one side (unilateral) or on both (bilateral).
Type of hearing loss:
Hearing loss is typically divided into three types: sensorineural, conductive,
and mixed.
Sensorineural - Hearing loss 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 - Hearing loss 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.
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 sensed by an individual.
Hearing losses are ranked as mild, moderate, severe or profound. The following
list shows the rankings and their corresponding decibel ranges:
- Mild - between 20 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
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:
Pre-lingual 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:
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.
Partial loss of hearing:
People who are hard-of-hearing have moderate amounts of hearing loss but
not enough to be considered deaf.
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 culturaly 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.