External cognition, interactivity and graphical representations

How can we optimise the potential benefits of new forms of interactive technologies for representing information? This paper is concerned primarily with CD-ROM formats but our analysis has a much wider applicability. Specifying how and why a virtual reality environment works, for example, will involve many of the same kinds of theoretical questions about the relationship between external and internal representations as for a paper-based diagram. Until we make progress with a more generalisable approach, then, we may remain as ad-hoc in our understanding as the designers we criticise so strongly