Dennis Hampton, Ph.D
280 Mamaroneck Ave.
White Plains, New York 10605
(914) 761-4455

Sensorineural Hearing Loss

Hearing loss has received a great deal of attention recently. The New York Times, CBS This Morning, Consumers Digest, Popular Science, National Public Radio and hundreds of other media have published or broadcast stories about recent advances in computer processing technology that have led to major improvements in hearing aids. And more attention has been directed at one of the major causes of hearing loss, noise.

Sensorineural hearing loss is the most common type of hearing loss in adults. According to the National Center for Health Statistics, 14% of adults between the ages of 45 and 64 years old have significant hearing loss and it has been estimated that 90% of those losses are sensorineural. Genetics, noise exposure, aging, viral infection, ototoxic drugs and physical trauma are all possible causes of sensorineural hearing loss. The results of a major university study suggest that hearing loss is the most common untreated problem in adults over 50 years of age.

Conductive hearing loss is less common and is seen more often in children. This type of loss is caused by a blockage of the ear, such as middle ear infection and impacted earwax.

A hearing loss is sensorineural if the problem involves the hearing organ itself (the cochlea), or the auditory neural system. In nearly all cases, the damage is in the cochlea itself and the more accurate (but less commonly used) terminology would be cochlear or inner ear hearing loss.

The chief characteristics of sensorineural (cochlear) hearing loss are:

  1. a greater loss of hearing for higher frequencies;
  2. a decreased ability to understand speech;
  3. a reduced tolerance for loud sounds.

These three characteristics can be understood by examining the structure of the inner ear.

High frequency hearing loss
The inner ear is built somewhat like a piano. That is, one end responds to low-frequency sounds, while the opposite end of the cochlea responds to high-pitched sound. Because the first signs of inner ear damage usually occur in the more exposed end that responds to high-pitches, the resulting hearing loss is first seen as a loss of sensitivity for high-frequency hearing.

Reduced speech discrimination
The healthy inner ear has between 15,000 and 20,000 inner ear cells. If half these cells are damaged, not only is there a loss of sensitivity to sounds, the ability of the inner ear to process sound has been compromised. Simply put, 10,000 hair cells cannot discriminate sounds as well as 20,000 hair cells can, and the ability to discriminate speech (or any sounds) is reduced, no matter how loud the sound. The result: the individual can hear speech, but cannot hear the difference between the words "thin" and "pin."

Reduced loudness tolerance
The third characteristic of sensorineural hearing loss is hypersensitivity to loud sounds, often referred to as recruitment.

Healthy cochlea cells are sensitive to very soft sounds. As sound gets louder, more cells are stimulated. But when inner ear cells are lost or damaged, softer sounds are not detected. Loud sounds are then suddenly "detected" by many hair cells. The sudden stimulation of many hair cells leads to a perception of abnormal loudness and hypersensitivity to loud sounds.

Hearing aids
Because sensorineural hearing loss is not the result of a blockage, but of damage to the inner ear itself, selecting and adjusting to hearing aids is more complex than selecting and adjusting to eyeglasses. Nevertheless, with professional help and the advanced technology available today-including hearing aids designed to fit each individual's hearing loss pattern and microprocessors that compensate for recruitment by automatically adjusting to changes in loudness-nearly anyone with sensorineural hearing loss can benefit from the use of hearing aids.