Hearing Impairment Definitions and Terms
Hearing impairment is a full or partial decrease in the ability to detect or understand sounds. It may be caused by a wide range of biological and environmental factors; loss of hearing can happen to any organism that perceives sound.
Hearing sensitivity is indicated by the quietest sound that an individual can detect, called the hearing threshold. In the case of people, this threshold can be accurately measured by a behavioral audiogram. A record is made of the quietest sound that the individual can hear for different frequencies (pitches). There are also electrophysiological tests that can be performed without requiring a behavioral response.
A hearing impairment exists when an individual is not sensitive to the sounds normally heard in the frequencies important for hearing speech. The severity of a hearing impairment is categorized according to how much louder a sound must be made over the usual levels before the listener can detect it. The ability to understand speech is another aspect to hearing that involves the quality of a sound rather than the loudness. That aspect is usually measured by tests using speech stimuli in quiet and sometimes in background noise which require that the sound is not only detected but understood.
Common Types and Causes of Hearing ImpairmentConductive Hearing Loss:
Occurs when sound is not conducted properly through the outer ear, middle ear, or both.
Conductive hearing loss has a variety of causes:
- Ear canal obstruction
- Abnormalities (such as rupture or scarring) of the tympanic membrane (eardrum)
- Abnormalities (such as breakage or stiffening) of the middle ear bones (ossicles)
- Selected abnormalities of the structure of the inner ear
- Physical trauma
Sensorineural hearing loss:
Occurs due to insensitivity of the inner ear, the cochlea, or to impairment of function in the auditory nervous system. This is classified as a disability under the ADA and if the person is unable to work s/he may be eligible for disability payments.
Sensorineural hearing loss has a variety of causes:
- Long-term exposure to environmental noise
- Disease or illness
- Medications/exposure to ototoxic chemicals
- Physical trauma