1. Hearing Disorders
The most common hearing disorders are those
that affect hearing sensitivity. When a sound is
presented to a listener with a hearing sensitivity
disorder, one of 2 things may occur:
1. The listener with a HS disorder may be unable
to detect the sound.
2. The sound will not be as loud to that listener as
it would be to a listener with normal hearing.
2. Note: Vision is different. The most common
vision disorders affect acuity, not sensitivity to
light. Acuity is the ability to resolve differences
amplifying it – but do not improve acuity.
Important: This sensitivity vs. acuity distinction
is not quite so simple with hearing (or vision):
hearing loss of any significance nearly always
involves problems of both sensitivity and acuity
– sounds are harder to hear (sensitivity) and they
are nearly always distorted (acuity). More about
this later.
3. The Audiogram
Most common way to measure hearing sensitivity is
to measure pure-tone (sinusoid) thresholds.
Threshold: Sound level required to barely detect a
sound.
5. Moderate-to-severe bilateral loss
Pure Tone Average (PTA)
Average thresholds at 500, 1000, 2000 Hz – the
frequencies most important for speech understanding.
From the audiogram above:
Pure-tone Average, Left Ear: 93 dB
Pure-tone Average, Right Ear: 50 dB
Severe loss
in left ear,
moderate
loss in right
ear.
6. Terminology
Normal Hearing: PTAs < 25 dB
Hearing Impairment: PTAs 25-92 dB
Deaf: PTAs > 92 dB
The term deafness is reserved for cases in which
“ … the handicap for hearing everyday speech …
[is] … total” (Davis & Silverman, 1979).
Despite these conventions: (1) there is no sharp
dividing line between hearing impairment and
deafness, and (2) degrees of deafness are
meaningful; e.g., there is a difference between
PTAs of 110 and 95.
7. Types of Hearing Disorders
Many ways to classify hearing disorders
1. Nature of the loss:
Sensitivity vs. Acuity
∙ Dysacusia – Deficit in discrimination or
interpretation of sound: “Don’t shout, I can
hear you just fine. I just can’t understand
what you’re saying.” Disacusia is a good
term that isn’t in very common use.
∙ Acuity deficits sometimes due to disorders
of the central auditory system.
∙ Disorders of sensitivity and acuity are not
mutually exclusive.
8. 2. Functional Classification
∙ Conductive – Disorders involving the
conduction of sound to the cochlea.
∙ Sensori-neural – Disorders involving the
cochlea (usually the hair cells) or 8th
N.
∙ Central – Disorders affecting the CNS (brain
stem or auditory cortex).
Two related terms:
Peripheral – Not central; i.e., conductive or
sensorineural.
Retrocochlear – Disorders involving anatomical
structures beyond the cochlea; i.e., 8th
N, brain
stem, auditory cortex.
9. 3. Cause or Etiology of the Disorder
Hearing disorders can be classified on the basis of
the cause of the disorder. Some examples:
∙ Ototoxic drugs
∙ Noise exposure
∙ Old age (presbycusis)
∙ Otitis media
∙ 8th
N tumors
∙ Meniere’s Disease
In this review, we will proceed by functional
subsystem (conductive, sensorineural, central), and
by etiology within each subsystem.
10. Conductive Hearing Disorders
1. External Ear
∙ Congenital malformations. There are many of
these. Most serious is congenital atresia –
collapse or closure of the EAM (ear canal). May
occur in isolation, but typically associated
congenital malformations of the middle ear as
well.
∙ Impacted wax (cerumen) – results in mild
hearing loss ; easily treated by removal of the
wax.
11. 2. Middle Ear
a. Otitis Media
∙ By far the most common cause of conductive
hearing loss.
∙ By far the most common health problem in
children.
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