There have been many different attempts to produce a model of a human being as an information processor. Many of these have attempted to describe a person math­ematically as an information processor in complex systems (see Timonen, 1980, for an overview of these). It is typical of these mathematical models that they can only handle a small part of human behaviour and as such their practical use is very lim­ited. They may be of some value in describing a particular form of behaviour in very critical and important situations—for example, an instrument monitoring the start­up of an aeroplane—but the value of such models is probably limited to helping in the structuring of the problems. On the other hand, the actual mathematical calcula­tions are of less interest. Singleton (1976), for example, stated that the mathematical descriptions are difficult and provide little extra information for the prediction of the operator’s behaviour. They are also often based on simulator studies, which always deviate to some extent from the real-life situation. Thus, the nonmathematical mod­els of a more general nature will be described in this section.

The aim of this type of model is to increase understanding of how a human works as an operator in a control room and to thereby improve and optimise the design and functioning of the control system. Models that describe a human being’s information processing capabilities and associated cognitive processes will be considered first. A discussion of the well-known mental models that humans use to assess the actual physical process is also presented (Bainbridge and Beishon, 1964; Crossman, 1965).