Synchronisation and Delay in a Formal Model of User Cognition

For the evaluation of the usability of interaction devices it is important to take the cognitive resources into account that a user needs to perform particular tasks. These aspects are dealt with mainly by usability testing and heuristics in a rather late stage in the design process. Although these approaches are important, they have also serious drawbacks. They do not support rigorous reasoning on the cogni-tive aspects of the usability of a device in the speciication phase of the development process. In this work we investigate a syndetic approach in which both a general cognitive model and a model of system behaviour are speciied and brought together within a single framework. The cognitive model, Interacting Cognitive Subsystems, has been subject of extensive psychological research and validation. Using it in an interface evaluation context requires however further formalization of the model. In this paper we show that a data ow model gives particularly interesting possibilities to investigate the consequences of a relative diierence in speed between the information processing of the human and the change of the environment in which (s)he is working.