Foundations for designing and evaluating user interfaces based on the crossing paradigm

Traditional graphical user interfaces have been designed with the desktop mouse in mind, a device well characterized by Fitts' law. Yet in recent years, hand-held devices and tablet personal computers using a pen (or fingers) as the primary mean of interaction have become more and more popular. These new interaction modalities have pushed the traditional focus on pointing to its limit. In this paper we explore whether a different paradigm—goal crossing-based on pen strokes—may substitute or complement pointing as another fundamental interaction method. First we describe a study in which we establish that goal crossing is dependent on an index of difficulty analogous to Fitts' law, and that in some settings, goal crossing completion time is shorter or comparable to pointing performance under the same index of difficulty. We then demonstrate the expressiveness of the crossing-based interaction paradigm by implementing CrossY, an application which only uses crossing for selecting commands. CrossY demonstrates that crossing-based interactions can be more expressive than the standard point and click approach. We also show how crossing-based interactions encourage the fluid composition of commands. Finally after observing that users' performance could be influenced by the general direction of travel, we report on the results of a study characterizing this effect. These latter results led us to propose a general guideline for dialog box interaction. Together, these results provide the foundation for the design of effective crossing-based interactions.