Redundancy and Adaptability

Extending an interaction to use more than one medium (or mode or channel) introduces the possibility of there being redundancy in the communication. This is an important opportunity because redundancy is a natural part of human communication. However, this chapter makes the additional point that redundancy in an interface also improves the possibilities for adapting it for use by people who have disabilities. Adapting computers for use by people with sensory disabilities is very much a problem of the interface. It seems likely that if several channels are utilized, then it should be possible to communicate (almost) as much information to a user who has a restriction in one as to an able-bodied user. If that is the case, then the users’ internal representations are likely to be almost identical. The deficits of disabled users’ cognitive models of the systems with which they interact are therefore due to the limits on the information they receive, rather than any inherent limitation in their ability to master complex systems. Vision has a very high bandwidth and tends therefore to dominate (as discussed in Chapter 1) and yet interface designers do not by any means make use of the full bandwidth of the other senses. For the average user some of that added information will be superfluous, redundant, but for others it may mean that communication is possible where it was not so previously.