A task analysis [20] will be carried out on the operator task to establish the information needs. These needs then must be characterized in terms of a defined information processing need using a knowledge characterization scheme. The options that the various media provide are then matched to the needs to obtain a set of multimedia possibilities. Finally, an envelope of defined interfaces can be derived by checking the possible interfaces against our knowledge of the human cognition system.

The knowledge characterization scheme identifies a number of important information communication features that describe the knowledge to be communicated to the operator, for example. More details are given in Alty and Bergan [3].

There are, of course, many more. We then map these information requirements onto appropriate media using another list of media properties, for example:

Finally, the options that result are examined for psychological appropriateness, i.e. those that best exploit the human cognition system. At this point, all objects currently being rendered (if known) are considered. An example of the sort of knowledge that is used in the psychological underpinning is the set of rules developed by Kosslyn et al. [13] - five principles of articulate graphics. Kosslyn points out that graphical displays must be articulate to succeed. They must transmit clear, compelling, and memorable messages. His five principles are:

For example, incremental transformation of images is important for creating and maintaining mental images. In the real world, objects do not disappear and reappear elsewhere. So pictures on VDU displays should change incrementally. Other important psychological principles are the 7 + 2 rule of Miller [16] and issues concerning the coherence or interference between visual and auditory channels. Application of the latter two rules, for example, make audio explanation with video highlighting a superior mechanism for explaining a complex diagram than the use of the visual channel only.