Today's graphical interactive systems largely depend upon pointing actions, i.e. entering an object and selecting it. In this paper we explore whether an alternate paradigm-- crossing boundaries -- may substitute or complement pointing as another fundamental interaction method. We describe an experiment in which we systematically evaluate two targetpointing tasks and four goal-crossing tasks, which differ by the direction of the movement variability constraint (collinear vs. orthogonal) and by the nature of the action (pointing vs. crossing, discrete vs. continuous). We found that participants ' temporal performance in each of the six tasks was dependent on the index of difficulty formulated in the same way as in Fitts' law, but that the parameters differ by task. We also found that goal crossing completion time was shorter or no longer than pointing performance under the same index of difficulty. These regularities, as well as qualitative characterizations of crossing actions and their application in HCI, lay the foundation for designing crossing-based user interfaces.

This paper is concerned with simple human performance “laws of action ” for three classes of tasks – pointing, crossing, and steering, as well as their applications in virtual reality research. In comparison to Fitts ’ law of pointing, the “law of steering ” – the quantitative relationship between human temporal performance and the movement path’s spatial characteristics – has been notably under investigated. After a historical review of research on the law of steering in different domains and time periods, we examine the applicability of the law of steering in a VR locomotion task. Participants drove a virtual vehicle in a virtual environment on paths whose shape and width were systematically manipulated. Results showed that the law of steering indeed applies to locomotion in virtual environments. Participants’ mean trial completion times linearly correlated (r² between 0.985 and 0.999) with an index of difficulty quantified as path distance to width ratio for the straight and circular paths used in this experiment. Their average mean and maximum speed was linearly proportional to path width. Such human performance regularity provides a quantitative tool for 3D human machine interface design and evaluation. We also propose to use the law of steering model in VR manipulation tasks such as the “ring and wire” task in the future.

We present an empirical analysis of crossing-based dialog boxes. First, we study the spatial constraints required for efficient crossing-based interactions in the case of a simple multi-parameter dialog box. Through a series of 3 tasks, we establish the minimal value of the landing margin, the takeoff margin, and the column width. We also offer an estimation of the role of stroke shape on user performance. After studying the reasons for errors during our experiment, we propose a relaxed crossing semantic that combines aspects of pointing and crossing-based interfaces. To test our design, we compare a naïve dialog box implementation with our new implementation, as well as a standard point-and-click dialog box. Our results reveal that there is not a significant difference between the naïve crossing implementation and the standard point-and-click interface and that the new crossing semantic is faster than both the naïve crossing implementation and the point-andclick interface, despite a higher error rate. Together these two experiments establish that crossingbased dialog boxes can be as spatially efficient and faster than their point-and-click counterpart. Our new semantic provides the first step towards a smooth transition from point-and-click interfaces to crossing-based interfaces.

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