Jerry: “Frank, why are you covering your ears?”
Frank: “I can’t stand the sound of those screaming children in the gym! Their screams are causing great pain in my ears! I have to leave!”
Recruitment is a term used to describe an abnormal growth of loudness. Recruitment may be present in people who have a sensorineural hearing loss but not all people with a sensorineural hearing loss suffer from recruitment. Recruitment can be mild or severe. People with normal hearing do not have recruitment.
How does this happen? Here is one explanation the some researchers believe to be the case. The hair cells in the inner ear (cochlea) are grouped together in critical bands. When any hair cell in a given critical band is stimulated, that entire critical band sends a signal to our brains which we “hear” as one unit of sound at the frequency that critical band is sensitive to. This is the situation when a person has normal hearing.
With a sensorineural hearing loss, some of the hair cells in the inner ear (cochlea) die or cease to function. When this happens, each “critical band” no longer has a full complement of hair cells. Our brains don’t like this condition. They require each critical band to have a full complement of hair cells. However, since all the hair cells are already in service in a particular band, there are no spares to recruit. Therefore, our brains recruit some hair cells from adjacent critical bands. These hair cells now have to do double duty or worse. They are still members of their original critical band and now are also members of one or more additional critical bands making the sound abnormally loud.
Appropriate hearing aids can help an individual hear well and at the same time protect them from sounds that can cause them extreme discomfort. I can remember a patient who loved to attend the Fort Wayne Komets hockey games. This patient had a severe hearing loss in one ear. When the loud horn went off during the hockey games, he could not stand the sound of the horn in the ear with the hearing loss. It caused significant pain in the ear with the severe hearing loss.
I recommended that he be fit with a behind-the-ear hearing aid with a fully occluding earmold. The goal was to force all sound entering the impaired ear to first pass through the hearing aid circuitry which would compress the sound of the horn and keep it comfortable. This arrangement worked very well. At the follow-up appointment in my office, the patient indicated that he could hear people in the aided ear and the sound of the horn and other loud sounds no longer bothered him.
With the new technology available in digital hearing aids, most patients can be protected from sounds that have caused pain. If you are suffering from recruitment, ask your physician to refer you to an audiologist.