User modelling and the design of computer-based assistive devices

User models are well represented in the field of human-computer interaction. They afford designers of interfaces detailed quantitative knowledge of the user for improved design, both in terms of the final end-product and the time taken to achieve this. However, they are almost always calibrated on able-bodied subjects using traditional input devices such as the keyboard and mouse. The ability to re-calibrate these models, or develop new ones, is essential for the successful design of assistive devices for the motion-impaired user. Computer-based assessment tools can be used to provide detailed information on user performance parameters. If designed well, these can provide the basis for a detailed user model. This paper presents a summary of the work currently being undertaken to develop a suite of such tools and the results obtained from user trials currently underway at the Papworth Trust. The paper also illustrates the practical applications of this work through the use of two examples: IRVIS (Interactive Robotic Visual Inspection System) and Jester (a gesture recognition system). It is the ability to analyse, and hence optimise, relatively complicated systems such as the IRVIS and Jester interfaces in terms of known user performance parameters that makes user models so useful. However, the results from user trials conducted to date shows that the existing models based primarily on able-bodied users do need refining and re-calibrating for the motion-impaired user.