ABSTRACT
The development of inexpensive computing resources has made it possible to design and produce a range of advanced cognitive artefacts. These artefacts are devices designed to maintain, display or operate upon information in order to serve a representational function. When used, they enhance human cognitive performance (Norman 1991). Performance is enhanced by changing the nature of the task performed rather than by changing the capability of the individual user. When the informational and processing structure of the artefact and the human user are combined in the execution of a task, there results an increase in capacity reflecting the total system of the human user, the task and the artefact.
