Users as rational interacting agents: formalising assumptions about cognition and interaction

Abstract

One way of assessing the usability of a computer system is to make reasonable assumptions about users’ cognition and to analyse how they can be expected to work with the system, using their knowledge and information from the display to achieve their goals. This is the approach taken in Programmable User Modelling Analysis, a technique for predictive usability evaluation of interactive systems. The technique is based on the premise that an analyst can gain insights into the usability of a computer system by specifying the knowledge that a user needs to be able to use it and drawing inferences on how that knowledge will guide the user’s behaviour. This may be done by observing how a cognitive architecture, “programmed” with that knowledge, behaves. An alternative approach is to develop a formal description of the essential features of the cognitive architecture and to use that description to reason about likely user behaviour. In this paper, we present the approach and an outline formal description of the cognitive architecture. This initial description is derived from an existing implementation. We illustrate how the description can be used in reasoning by applying it to the task of setting up call diverting on a mobile phone. Successful performance of this task involves a combination of planned and responsive behaviour. The process of doing this analysis highlights what assumptions have been made by the designers about the user’s knowledge. We discuss limitations of the current formalisation and identify directions for future work.