Computational modeling of user errors for the design of virtual scanning keyboards

Virtual scanning keyboards are used by persons with severe speech and motion impairments as communication aids. Each of these systems consists of a virtual keyboard and a "scanning and access switch" based alternate input method. Designers of such keyboards face problems due to the difficulties in testing prototypes with disabled users. Model-based design approaches were proposed in order to alleviate the problems. In model-based design, systems are evaluated with user models reducing the need for extensive user testing. The existing model-based approaches, however, do not consider the effect of user errors in evaluating systems. The lack of consideration of errors limits the practical usefulness of the resulting designs. To overcome this limitation, we have performed empirical studies of errors on virtual scanning keyboards. From our study results, we have derived predictive models of user's error behavior. We have used the models to develop "ErrorProneness," a numerical error measure for virtual scanning keyboards. We have proposed a method using the "ErrorProneness" measure for taking the effects of errors into account in model-based design. Methods employed in our study, results obtained, the predictive user models, the error measure, and the proposed design method are presented in this paper.