from Medical topics
Published online by Cambridge University Press: 18 December 2014
Hearing loss that is acquired after the development of language is distinct from pre-lingual hearing loss in its psychological and social manifestations. This chapter is concerned with hearing loss that occurs after the development of language.
Audiological background
Hearing loss is categorized by the site of the lesion causing the loss. A lesion of the outer ear, ear drum or middle ear causes a conductive hearing loss, due to a reduction in hearing sensitivity. A cochlear hearing loss may lead to reduced auditory discrimination as well as reduced hearing sensitivity. A lesion affecting the auditory nerve may also cause reduced sensitivity and discrimination. Finally, a category of Central Auditory Processing Disorder (CAPD) has been identified in which cochlear function may be normal, but the person has auditory perceptual problems particularly in the presence of background noise. The categories of cochlear, retro-cochlear and central auditory dysfunction are referred to as sensori-neural hearing loss (SNHL). Most adults with an acquired hearing loss have cochlear dysfunction, with the most common aetiology being age-related hearing loss. Davis (1997) reported that 13.9% of the adult population (aged 18–80) have a SNHL equal to, or worse than, 25 dB (the level of a whisper) in the better ear. This prevalence rises with age such that 42% of elderly people have such a loss. This criterion of SNHL represents the point at which an individual might benefit from a hearing aid.
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