- Hearing loss is defined as diminished acuity to sounds which would otherwise be heard normally.The terms hearing impaired or hard of hearing are usually reserved for people who have relative inability to hear sound in the speech frequencies. The severity of hearing loss is categorized according to the increase in intensity of sound above the usual level required for the listener to detect it.
- Deafness is defined as a degree of loss such that a person is unable to understand speech, even in the presence of amplification.In profound deafness, even the highest intensity sounds produced by an audiometer (an instrument used to measure hearing by producing pure tone sounds through a range of frequencies) may not be detected. In total deafness, no sounds at all, regardless of amplification or method of production, can be heard.
- Speech perception is another aspect of hearing which involves the perceived clarity of a word rather than the intensity of sound made by the word. In humans, this is usually measured with speech discrimination tests, which measure not only the ability to detect sound, but also the ability to understand speech. There are very rare types of hearing loss that affect speech discrimination alone. One example is auditory neuropathy, a variety of hearing loss in which the outer hair cells of the cochlea are intact and functioning, but sound information is not faithfully transmitted by the auditory nerve to the brain.
Use of the terms “hearing impaired”, “deaf-mute”, or “deaf and dumb” to describe deaf and hard of hearing people is discouraged by many in the deaf community as well as advocacy organizations, as they are offensive to many deaf and hard of hearing people.
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