3.3 Deaf and hard of hearing
The World Health Organization (WHO) defines deafness as complete loss of the ability to hear from one or both ears. This is profound hearing impairment -- 81 dB or greater hearing threshold, averaged at frequencies 0.5, 1, 2, 4 kHz. The WHO defines hearing impairment as a complete or partial loss of the ability to hear from one or both ears. This represents mild or worse hearing impairment of a 26 dB or greater hearing threshold, averaged at frequencies 0.5, 1, 2, 4 kHz.91 Some 250 million people in the world are estimated as having a disabling hearing impairment.92
The barriers encountered by children with a hearing impairment in inclusive schools relate primarily to communication.
Assistive technologies for hearing
The predominant AT used by people with a hearing impairment is a hearing aid. Hearing aids amplify sound from the surrounding environment, but may also be used to amplify signals produced by a T-loop system.93 A T-loop picks up audio from a microphone and transmits a signal within the area of a wire loop directly to a compatible hearing aid.
Issues encountered by deaf people when using a computer to access electronic content relate primarily to audio. Captioning is the rendering of speech and other audible information in the written language of the audio. Captions can be closed, meaning that they are encoded and can be toggled on or off if the user’s browser or media player can decode them. Or, they are open -- they are presented at the same time as the visual content. Captions are more sophisticated than subtitles, which are suited for hearing people who do not understand the language of the content. Captions may provide meta-information about who is speaking or the tone of the voice, and they can denote other sounds that occur on the sound-track of the content.
World Wide Web authors are becoming aware of the need to develop caption and file formats that accommodate a captioning track. Caption-authoring packages are available to add multimedia, overlay captioning to computer-based video.94 The online video-sharing website YouTube has introduced an automatic captioning service.95
Text transcripts or captions for learning resources or training materials enable access to these materials by literate students with hearing impairments. Text captions also aid comprehension by students whose first language is that not that of the course material.
Many deaf people96 use sign language, which they may consider to be their first language. Sign language may also be used in audio/visual materials, with a sign language interpreter appearing in the bottom right corner of the screen to provide a sign language interpretation of the speech in the audio track.
The following video shows how the use of captions and audio descriptions are essential for both deaf and blind students in the use of educational materials.