Systematic user errors commonly occur in the use of interactive systems. We describe a formal reusable user model implemented in higher-order logic that can be used for machine-assisted reasoning about user errors. The core of this model is a series of non-deterministic guarded temporal rules. We consider how this approach allows errors of various specific kinds to be detected by proving a single theorem about a device. We illustrate the approach using a simple case study.

Objective: To replicate a successful laboratory slip-class error paradigm and, more importantly, to further understand the underlying causes of errors made in that paradigm. Background: Routine procedural errors are facts of everyday life but have received limited controlled empirical study, despite the sometimes severe consequences associated with such errors. This research concerns one such error, postcompletion error (M. D. Byrne & S. Bovair, 1997), which is a lapse that occurs after the main goal of a task has been satisfied. Method: In the two experiments conducted, participants were trained to criterion on a routine procedural task and were then brought back to the lab for a later session or sessions in which performance on task execution was measured. In the second experiment, a variety of motivational manipulations, retraining, and task redesign were compared. Results: Experiment 1 demonstrated a substantial reduction of error rate generated by a simple design change (alteration of when feedback about goal completion occurred). Furthermore, the reduction in error rate came with no penalty in terms of overall speed of performance. Experiment 2 showed that this more appropriate design is superior to motivationally oriented interventions, retraining, and even midtask redesign. As in Experiment 1, Experiment 2 revealed no speed-accuracy tradeoff. Conclusion: These experiments provide evidence that controlled laboratory studies of slip-class errors can be meaningful and highlight the centrality of cognitive factors (particularly goal structure) in such errors. Application: Potential applications include design of interfaces and their related procedures as well as error-mitigation techniques.