Written by Courtney Morrison, Clinical Audiologist
The human ear is
remarkably sensitive to a huge range of sound levels. For example, the sound
generated by a jet engine, at 120 decibels, is a trillion times more intense
than the sound level at the threshold of hearing and the intensity of a normal
conversation can be 10 000 times greater than that of a whisper. With hearing loss, hearing thresholds increase
and soft, low-intensity sounds become inaudible. However, for some individuals,
both with and without hearing loss, everyday
noises can seem intolerably loud. Why is this?
Source
|
Intensity Level
|
Times
Greater Than
Threshold Of Hearing
|
Threshold
of hearing (TOH)
|
0
dB
|
100
|
Rustling
leaves
|
10
dB
|
101
|
Whisper
|
20
dB
|
102
|
Normal
conversation
|
60
dB
|
106
|
Busy
street traffic
|
70
dB
|
107
|
Vacuum
cleaner
|
80
dB
|
108
|
Large
orchestra
|
98
dB
|
109.8
|
Front
row of rock concert
|
110
dB
|
1011
|
Gun
shot at close range
|
140
dB
|
1014
|
What is hyperacusis?
Þ hyper–
above; excessive
–acusis,
hearing
Hyperacusis is an
unusually low tolerance to everyday sounds which are tolerable for most
listeners. Individuals who experience hyperacusis often try to avoid sounds or
environments that they perceive to be too loud, or will grimace or cover their
ears when they encounter them. There are estimates that 40-86% of people who
report this also report tinnitus and while it often accompanies a damaged
auditory system many sufferers present with no obvious hearing loss.
While there is no
conclusive evidence as to what causes hyperacusis, it has been suggested that
it is related to neurotransmitter activity in the brain, and is influenced by
stress, anxiety and fatigue, not unlike tinnitus.
What is recruitment?
A large increase in the
sensation of loudness with only a slight increase in the actual intensity of
sound is what is known as recruitment. If you’ve ever tried to get the
attention of someone with a hearing loss a couple of times at your normal
speaking level, before raising your voice to a somewhat louder volume, and been
met with the response “no need to yell, son” you have experienced hearing
recruitment. Recruitment is associated with sensorineural, or inner ear hair
cell damage. At some decibel level of sound, functional hair cells adjacent to
the damaged hair cells kick in, or are recruited, resulting in a sudden boost
in the perceived loudness of the sound.
What can be done to
manage hyperacusis and recruitment?
Today’s hearing aids have
a feature called Wide Dynamic Range Compression (WDRC) which is designed to
make soft sounds audible, and loud sounds tolerable, meaning it works great for
individuals with recruitment.
For patients with
hyperacusis, often the first instinct is to protect their ears with plugs,
muffs or other devices. Constant use of ear plugs, however, can have the
adverse effect, accentuating the loudness of the environment when the plugs are
removed. Instead, the approach
increasingly recommended by hearing professionals is to desensitize the ears
using noise stimulation, in much the same way you would use a noise masker or
sound therapy for tinnitus, and to counsel the patient following a thorough
history-taking and audiological assessment.