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Imagine trying to drive a car by using just a computer keyboard. The four arrow keys are used for steering, the space bar for braking, and the return key for accelerating. To indicate left you need to press the F1 key and to indicate right the F2 key. To sound your horn you need to press the F3 key. To switch the headlights on you need to use the F4 key and, to switch the windscreen wipers on, the F5 key. Now imagine as you are driving along a road a ball is suddenly kicked in front of you. What would you do? Bash the arrow keys and the space bar madly while pressing the F4 key? How would you rate your chances of missing the ball?

Most of us would balk at the very idea of driving a car this way. Many early video games, however, were designed along these lines: the user had to press an arbitrary combination of function keys to drive or navigate through the game. There was little, if any, consideration of the user's capabilities. While some users regarded mastering an arbitrary set of keyboard controls as a challenge, many users found them very limiting, frustrating, and difficult to use. More recently, computer consoles have been designed with the user's capabilities and the demands of the activity in mind. Much better ways of controlling and interacting, such as through using joysticks and steering wheels, are provided that map much better onto the physical and cognitive aspects of driving and navigating.

In this chapter we examine some of the core cognitive aspects of interaction design. Specifically, we consider what humans are good and bad at and show how this knowledge can be used to inform the design of technologies that both extend human capabilities and compensate for their weaknesses. We also look at some of the influential cognitively based conceptual frameworks that have been developed for explaining the way humans interact with computers. (Other ways of conceptualizing human behaviour that focus on the social and affective aspects of interaction design are presented in the following two chapters.)

The main aims of this chapter are to: