Modeling and predicting pointing errors in two dimensions

Recently, Wobbrock et al. (2008) derived a predictive model of pointing accuracy to complement Fitts ’ law’s predictive model of pointing speed. However, their model was based on one-dimensional (1-D) horizontal movement, while applications of such a model require two dimensions (2-D). In this paper, the pointing error model is investigated for 2-D pointing in a study of 21 participants performing a time-matching task on the ISO 9241-9 ring-of-circles layout. Results show that the pointing error model holds well in 2-D. If univariate endpoint deviation (SDx) is used, regressing on N=72 observed vs. predicted error rate points yields R 2 =.953. If bivariate endpoint deviation (SDx,y) is used, regression yields R 2 =.936. For both univariate and bivariate models, the magnitudes of observed and predicted error rates are comparable. Author Keywords: Pointing error model, Fitts ’ law, metronome, movement time, error prediction, error rates

Automatically Generating Personalized User Interfaces with SUPPLE

Today's computer–human interfaces are typically designed with the assumption that they are going to be used by an able-bodied person, who is using a typical set of input and output devices, who has typical perceptual and cognitive abilities, and who is sitting in a stable, warm environment. Any deviation from these assumptions may drastically hamper the person's effectiveness—not because of any inherent barrier to interaction, but because of a mismatch between the person's effective abilities and the assumptions underlying the interface design. We argue that automatic personalized interface generation is a feasible and scalable solution to this challenge. We present our Supple system, which can automatically generate interfaces adapted to a person's devices, tasks, preferences, and abilities. In this paper we formally define interface generation as an optimization problem and demonstrate that, despite a large solution space (of up to 1017 possible interfaces), the problem is computationally feasible. In fact, for a particular class of cost functions, Supple produces exact solutions in under a second for most cases, and in a little over a minute in the worst case encountered, thus enabling run-time generation of user interfaces. We further show how several different design criteria can be expressed in the cost function, enabling different kinds of personalization. We also demonstrate how this approach enables extensive user- and system-initiated run-time adaptations to the interfaces after they have been generated. Supple is not intended to replace human user interface designers—instead, it offers alternative user interfaces for those people whose devices, tasks, preferences, and abilities are not sufficiently addressed by the hand-crafted designs. Indeed, the results of our study show that, compared to manufacturers' defaults, interfaces automatically generated by Supple significantly improve speed, accuracy and satisfaction of people with motor impairments.Engineering and Applied Science

Understanding Expressions of Unwanted Behaviors in Open Bug Reporting

Open bug reporting allows end-users to express a vast array of unwanted software behaviors. However, users ’ expectations often clash with developers’ implementation intents. We created a classification of seven common expectation violations cited by endusers in bug report descriptions and applied it to 1,000 bug reports from the Mozilla project. Our results show that users largely described bugs as violations of their own personal expectations, of specifications, or of the user community’s expectations. We found a correlation between a reporter’s expression of which expectation was being violated and whether or not the bug would eventually be fixed. Specifically, when bugs were expressed as violations of community expectations rather than personal expectations, they had a better chance of being fixed. 1