A historical perspective. When the interest in the use of information technology and telecommunications by and for people with activity limitations started, the situation was relatively simple: the main service for interpersonal communication was the telephone, and information was distributed by means of radio and television. Computers were mainly stand-alone units used in closed and specialised communities (e.g. those of scientists and businessmen) (Emiliani 2009). In principle, the telephone was a fundamental problem only for profoundly deaf people. For all other groups of people with activity limitations, solutions were within the reach of relatively simple technological adaptations. The technology used for implementing the telephone lent itself to the possibility of capturing the signal (electromagnetic induction) and making it available for amplification for deaf people. Even the problems of profoundly deaf people were facilitated by the telephone system itself, when it was discovered that the telephone line could be used to transmit digital data (characters) with suitable interfaces (modems). Radio was an important medium for the diffusion of information. In principle, radio can represent a problem for deaf people. But since amplification is inherent in a radio system, problems occur again therefore only for profoundly deaf people. Television was the first example of a service that used the combination of the visual and acoustic modalities, not redundantly, but for conveying different types of information. Being more complex, television could create more difficulties for people with activity limitations, but it had inherent capabilities for overcoming some of the problems. It is evident that television can create problems to blind, visually-disabled and deaf people. On the other hand, the fact that additional information can be transmitted by exploiting the available bandwidth enables support for people with activity limitations to be added to the standard service. Therefore, programmes can be subtitled for deaf people, and scenes without dialogue can be described verbally for blind people. In addition, text services can be set up (e.g. televideo, teletext), thus solving some of the problems related to the accessing of information by profoundly deaf people. Television is a simple example of a general situation. An increase in the complexity of a system or service increases the number and extent of problems that such a system or service can create for people who have reduced a...
