Before we can understand hearing loss, we must first
understand what hearing entails. When we hear sounds, we really are
interpreting patterns of movement of air molecules. We can describe sounds
in terms of their frequency (or pitch) and intensity (or loudness).
Frequency is measured in hertz (Hz). A person who has hearing within the
normal range, can hear sounds that have frequencies between 20 and 20,000
Hz. The most important sounds we hear every day are in the 250 to 6,000 Hz
range. Speech includes a mix of low and high frequency sounds. Vowel
sounds like “u” have low frequencies (250 to 1,000 Hz) and are usually
easier to hear. Consonants like “s,” “h,” and “f” have higher frequencies
(1,500 to 6,000 Hz) and are harder to hear. Consonants convey most of the
meaning of what we say. Someone who cannot hear high-frequency sounds will
have a hard time understanding speech.
Intensity, or loudness, is measured in decibels (dB). A
person with hearing within the normal range can hear sounds ranging from 0
to 140 dB. A whisper is around 30 dB. Conversations are usually 45 to 50
dB. Sounds that are louder than 90 dB can be uncomfortable to hear. A loud
rock concert might be as loud as 110 dB. Sounds that are 120 dB or louder
can be painful and can result in temporary or permanent hearing loss.
Impairments in hearing can happen in either frequency
or intensity, or both. Hearing loss severity is based on how well a person
can hear the frequencies or intensities most often associated with speech.
Severity can be described as mild, moderate, severe, or profound. The term
“deaf” is sometimes used to describe someone who has an approximately 90 dB
or greater hearing loss or who cannot use hearing to process speech and
language information, even with the use of hearing aids. The term “hard of
hearing” is sometimes used to describe people who have a less severe
hearing loss than deafness.
Hearing loss can affect one or both ears. A loss that
affects one ear is called a unilateral loss. A loss that affects both ears
is called a bilateral loss.
There are four main types of hearing loss:
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Conductive: Hearing loss caused by a problem
in the outer ear or middle ear. Conductive losses usually affect all
frequencies to the same degree. These losses are not usually severe.
-
Sensorineural: Hearing loss caused by a
problem in the inner ear or auditory nerve. A sensorineural loss often
affects a person’s ability to hear some frequencies more than others.
This means that sounds may be appear distorted, even with the use of a
hearing aid. Sensorineural losses can range from mild to profound.
-
Mixed: A combination of conductive and
sensorineural losses.
-
Central: Hearing loss caused by a problem
along the pathway from the inner ear to the auditory region of the brain
or in the brain itself.
Approximately 30% of children who are deaf or hard of
hearing also have one or more other developmental disabilities, such as
mental retardation, cerebral palsy, vision impairment, or epilepsy. [Read
more about developmental disabilities]
Hearing loss can affect a child’s ability to learn both to speak and to
understand spoken language. This is especially true if the child is born
with a hearing loss or loses his or her hearing before 2 years of age.
People with hearing loss may communicate using speech (sometimes called
oral communication), sign language (sometimes called manual communication),
or a combination of both. Oral communication focuses on speech, listening
with hearing aids, and sometimes lipreading. Manual communication includes
sign language.
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Date: October 29, 2004
Content source: National Center on Birth Defects and Developmental
Disabilities