Much of what is of practical interest in this chapter involves the choice of simple actions. For a more comprehensive account a wider range of human activities would need to be examined, ranging from the quite lowly ones which we shall in fact concentrate on, to the complex ones like chess and computer programming dealt with elsewhere (Anderson 1980) which depend on comparatively highorder cognitive processes. The former are mainly quite simple motor actions and often relate to questions to do with the design of equipment: like what should be the relative positions in the cockpit of an aircraft of the various instruments and controls used by the flight crew; or, more mundanely, where should the burners of a cooker be situated in relation to the controls to activate them. The interest lies in how to design and deploy the displays and controls which mediate people’s actions on the world, and particularly their actions on machines and complex systems like computers. The psychological theory and conceptual analysis underlying the practical conclusions that may be reached are comparatively undeveloped, although there have been some very useful insights in the last few years. Interpretations which refer to ‘procedural knowledge’

(Anderson 1980), and to ‘mental models’ (Aitkenhead and Slack 1985) are feasible in an information-processing framework, but we shall have more basic theoretical questions in view. The applications context of this chapter is one in which some unusually well-defined and concrete questions may be posed. What is unusual is that the tangible context for the application of psychology is readily apparent, as can be seen from the cockpit and cooker examples just mentioned.