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An auditory disorder effecting the perception of sound volume. In recruitment, sound intensifies from inaudible to blaring across the gradient of a few decibels. Slightly raising the volume of your voice can cause a recruitment sufferer to accuse you of shouting at them. This condition is distinct from hyperacusis in that recruitment is always the result of sensorineural hearing loss. Like hyperacusis, recruitment is comorbid with tinnitus, a ringing in the ears.

The genesis of recruitment can be found in the nature of hearing loss. In the ear, healthy hair cells are arranged in “critical bands”, groupings of cells that correspond to specific frequencies. When a critical band is activated, a signal is sent to the brain to indicate the nature and composition of a sound. In an ear with hearing loss, hair cells are damaged or die and the brain “recruits” adjacent cells to engineer a full complement of bands. If the damage is severe enough, one hair cell may belong to several bands at once. This creates a situation akin to a row of tuning forks, stood up like dominos. Because of the hearing loss, a person’s threshold of activation is abnormally high, but when it is reached, it activates several critical bands at once, making the sound appear to be much louder than it is.

Additionally, recruitment often presents as severe distortion for audible sound. Instead of perceiving a sound as being one frequency, it is perceived as being several different frequencies at once, making speech nothing but unintelligible noise.

Since most people who suffer from recruitment wear hearing aids, an audiologist must test each frequency in ascending decibel levels, until the patient’s gradient of comfort is established. It is only then that hearing aids can be properly calibrated to avoid discomfort.