Hearing Impairment

Hearing impairment is a full or partial decrease in the ability to detect or understand sounds. Caused by a wide range of biological and environmental factors, loss of hearing can happen to any organism that perceives sound. Sound waves vary in amplitude and in frequency. Amplitude is the sound waves highest point of oscillation. Frequency is the speed of sound divided by the wavelength of the sound wave, which is referred to as the pitch of the sound. Therefore losing the ability to detect some frequencies, or very soft sounds, that an organism naturally detects, creates some form of hearing impairment.

There are many causes of hearing loss, such as exposure to loud noises over a prolonged period of time or aging. Over the course of a person's life the quality of their hearing will, in most cases, become less. This is most likely due to loud noise, disease/illness, or its inherited from the parent.

Most sensory hearing loss is due to poor hair cell function. The hair cells may be abnormal at birth, or damaged during the lifetime of an individual. There are both external causes of damage, like noise trauma and infection, and instrinsic abnormalities, like deafness genes.  Sensory hearing loss that results from abnormalities of the central auditory system in the brain is called Central Hearing Impairment. Since the auditory pathways cross back and forth on both sides of the brain, deafness from a central cause is unusual.

In addition to hearing aids there exist cochlear implants of increasing complexity and effectiveness. These are useful in treating the mild to profound hearing impairment when the onset follows the acquisitions of language and in some cases in children whose hearing loss came before language was acquired. Recent research shows variations in effacacy but some promising studies show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech.

...More at Wikipedia

Related Links:

• National Association of the Deaf
• Mayo Clinic

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