Telecommunication interfaces for deaf people

The telephone is used daily by several million of people with some degree of hearing loss. In most cases a version of the ordinary telephone is used, with the required amplification (over and above that provided by the network) `added´ using a telephone mounted gain control and/or a hearing aid. Text telephony (which is discussed) is used by deaf people whose degree or type of hearing loss is such that they are unable to benefit from amplification of telephone signals. Those who are profoundly or severely deaf (>85dBHL loss) may be considered the main users (and potential users) of text telephones and associated services. In addition people who are deaf-blind and those who are speech impaired can also benefit from text telephony. A typical text telephone unit comprises a microprocessor controlled terminal consisting of a single line display scrolling left/right or right/left and displaying upper case characters only, an alphanumeric full travel keyboard (providing access to a subset of International Alphabet number 5), and some means of enabling connection to the public switched telephone network (PSTN), either directly or by acoustic coupling. User interfaces for such text telephones are discussed