Enabling devices, empowering people: the design and evaluation of Trackball EdgeWrite

To describe the research and development that led to Trackball EdgeWrite, a gestural text entry method that improves desktop input for some people with motor impairments. To compare the character-level version of this technique with a new word-level version. Further, to compare the technique with competitor techniques that use on-screen keyboards.

A rapid and iterative design-and-test approach was used to generate working prototypes and elicit quantitative and qualitative feedback from a veteran trackball user. In addition, theoretical modelling based on the Steering law was used to compare competing designs.

One result is a refined software artifact, Trackball EdgeWrite, which represents the outcome of this investigation. A theoretical result shows the speed benefit of word-level stroking compared to character-level stroking, which resulted in a 45.0% improvement. Empirical results of a trackball user with a spinal cord injury indicate a peak performance of 8.25 wpm with the character-level version of Trackball EdgeWrite and 12.09 wpm with the word-level version, a 46.5% improvement. Log file analysis of extended real-world text entry shows stroke savings of 43.9% with the word-level version. Both versions of Trackball EdgeWrite were better than on-screen keyboards, particularly regarding user preferences. Follow-up correspondence shows that the veteran trackball user with a spinal cord injury still uses Trackball EdgeWrite on a daily basis 2 years after his initial exposure to the software.

Trackball EdgeWrite is a successful new method for desktop text entry and may have further implications for able-bodied users of mobile technologies. Theoretical modelling is useful in combination with empirical testing to explore design alternatives. Single-user lab and field studies can be useful for driving a rapid iterative cycle of innovation and development.