Sound Sensitivity

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.