In any animation there are two sorts of visual objects ones that form the ground on which other objects play. Ground objects are often static, or have contained movement (the swirling of water, the waving of trees, the drift of clouds), and these contrast with the figure objects which are (or appear to be) motivated . That is to say their movement has apparent purpose either in an anthropomorphic sense in that we can understand their actions and the motives for them, or in the way in which there is a play of cause and effect. It is these motivated objects, representational images of people, mice, ducks, cats, steam trains, that come to life , are animated in moving image sequences. Even if the animated world exaggerates or contradicts the rules of cause and effect as we know them from our day-to-day experiences, we quickly learn and accommodate the difference and derive pleasure from it.

In multimedia there is an extended range of objects, and a blurring of the distinction between them. Again there are ground objects, either as static images or as contained animations cycling away, and there are motivated objects which move around or change independently. In addition there are responsive objects, things that move or change in response to the viewer's actions and interventions, such as a button that changes colour when the mouse is clicked on it.

It is in the presence of responsive objects that the particular concerns of...