Prevalence, Definitions, and Characteristics
Individuals with hearing impairments make up .11% of the school-age population, and 1.2% of the students served under IDEA (U.S. Department of Education, 2005). Hearing impairments range in severity from mild to moderate to severe to profound, with the greatest educational distinctions occurring between hard of hearing and deaf. Individuals classified as hard of hearing can hear speech tones when wearing hearing aids, while persons who are deaf cannot hear even with hearing aids.
The age that a child loses hearing affects the degree of language delay and development. Children who are born with deafness have congenital hearing losses (prelingual) and more difficulty with language development than those who acquire deafness after age 2 (postlingual).
Pure tone audiometers are used to assess hearing ability. Tones with different pitches (or frequency measured in Hertz [Hz]) and volume (measured in decibels [dB]) are presented via headphones, and individuals raise their hand when they hear a sound. Levels of hearing impairment are classified along a continuum, with reference to zero dB indicating the quietest sound a person with normal hearing can detect. Individuals with slight hearing losses (27–40 dB) may not have difficulty in most school situations. Individuals with mild losses (41–55) may miss up to 50% of classroom discussion if voices are faint or faces cannot be seen. Individuals with moderate losses (56–70 dB) can understand only loud speech, and may have limited vocabularies. Individuals with severe losses (71–90 dB) may be able to hear loud voices within one foot from the ear, and speech is likely to be impaired. Individuals with profound losses (> 90 dB) may hear some loud sounds, but are more likely to sense vibrations, and may rely on vision rather than hearing as a primary vehicle for communication (Heward, 2006). Specialized tests are needed to accurately assess the cognitive and academic functioning of individuals with hearing impairments (Owens, Metz, & Haas, 2003).
Causes of hearing impairments include heredity, prenatal infections such as maternal rubella, ear infections, meningitis, head trauma, prematurity, and oxygen deprivation. Impairments can be conductive, meaning the outer or middle ear along the passageway are damaged; sensorineural, referring to inner ear damage; or they can be a combination of the two (Owens, Metz, & Haas, 2003).
Many children with hearing impairments have academic and cognitive deficiencies or developmental lags due to difficulties processing language (Meadow-Orlans, 1990). Some children experience social-emotional functioning difficulties due to communication difficulties (Luterman, 1996).
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