How we hear
Sound is the result of vibration. It is the movement of air particles, that are perceived in
both frequency (pitch) and intensity (loudness). Frequency or pitch is the number of cycles
per second at which any sound is vibrating. Most sounds are complex and they are made up of a
combination of many frequencies. The less a sound vibrates, (or less cycles per second) the
lower the pitch of the sound. For example, a refrigerator hum is a low frequency sound.
The more a sound vibrates, the higher the pitch of the sound. For example, sirens, birds and
crickets are typically high pitch sounds.
When we test hearing, we test a variety of sounds from low pitch to high pitch. We do this to
determine how well each person hears each of these sounds. If a hearing loss is present, we
can see from the audiogram, which sounds will be affected and how much difficulty one will have with
the understanding of speech. Vowels are primarily composed of low-pitched sounds. If you
place your hand on your throat and say the vowel sounds, you will feel the intensity of sound.
They are voiced sounds. There is power and loudness when you say them. If you repeat
consonant sounds, for example, p, b, t, s, k, and so forth, there is no intensity of sound.
The consonants are unvoiced and therefore very soft.
About twenty one million Americans, infants, children, adults, and senior citizens have a hearing
impairment in one or both ears. Some never suspect a problem. Many people lose their
hearing, particularly through the aging process have better hearing in the low frequency range, and
poorer hearing in the high frequency range. For that reason, often they can hear speech but
are not able to make out the words. They are hearing sound in a distorted manner. They
may hear the low frequency components, but because the high frequency portion is too soft or
sometimes not heard at all, it is very difficult to differentiate one word from another. Hearing
aids, particularly the more advanced digital and programmable hearing aids are especially effective
for people who could not benefit from hearing aids previously.
The ear consists of three main parts:
The outer ear consists of the pinna, the ear canal, and the eardrum.
The middle ear is a small, hollow air filled cavity behind the eardrum. The smallest bones of
the body, the malleus, incus and stapes are located in the middle ear. The malleus is attached
to the eardrum. The incus connects the malleus to the stapes. The footplate of the
stapes is imbedded in the oval window of the cochlea. They all work together in a chain to
mechanically transmit sound.
The inner ear, or cochlea, is a snail shaped structure that is filled with fluid and tiny hair
cells. Their function is to send nerve impulses to the brain. Most people with hearing
losses due to the aging process and many, who have hearing losses for other reasons, have them
because of damage to this area.
The balance mechanism (semicircular canals) is a structure that sits on top of the cochlea. It
is responsible for letting you know what position you are in relative to your surroundings. It
is fluid filled and is very sensitive to changes in your orientation to the world.
Occasionally a person, who has a hearing loss, also has a problem with balance or dizziness.
Testing is necessary to determine if this is related to the hearing loss or to another medical
condition.
When sound enter the ear, it makes the eardrum vibrate.
Because the ear drum is attached to the grouping of middle ear bones, they
in turn, vibrate. The last bone, the stapes, pushes into the oval
window of the cochlea and because the fluid is disrupted by this, the tiny
hair cells are stimulated and they send nerve impulses to the auditory
nerve which then sends the sound to the brain. The outer hair cells
respond to soft sounds while the inner hair cells are activated by more
intense sounds. These responses send nerve impulses to the brain to
the auditory cortex to allow you to process sound.
When there is a problem with any one of the parts of the
hearing mechanism, whether located in the outer, middle or inner ear, a
hearing loss is present. If a hearing loss is located in the outer
or middle part of the ear, a conductive hearing loss is present.
Many conductive hearing losses can be corrected by medical intervention.
Some of the reasons for a conductive loss may be simple, such as impacted
cerumen (wax) in the ear canal, or be the result of infection, perforated
eardrum(s), otosclerosis, recurrent ear infections or mastoiditis.
When a conductive component is identified, the patient will be referred
for additional medical consultation to determine if medical or surgical
treatment is indicated. If it is not, the patient may be a candidate
for amplification.
A sensorineural hearing loss is one in which the damage
to your hearing mechanism has taken place in the cochlea or auditory
nerve. Most nerve losses are cochlear in site. If a
sensorineural loss is present, you may be a candidate for a trial period
with hearing aids.
