User performance with trackball-mice

Trackball-mice are devices that include both a trackball and a mouse. In this paper we discuss our experiences in building and testing trackball-mouse prototypes. We report four experiments on user performance with the prototypes used as trackball-mice, conventional mice, and in two-handed configuration with a separate trackball for the non-dominant hand. The results show that user performance with the two-handed configuration was better than in one-handed operation of a trackball-mouse and in one-handed operation of a mouse. Trackball-mouse use and conventional mouse use were more evenly matched. However, Trackball-mouse operation involves a skill that most users do not have whereas mouse operation is familiar to most. Therefore, widespread introduction of trackball-mice does not appear to be justified on performance grounds alone. However, trackball-mice can be used as regular mice by ignoring the ball. This makes them compatible with traditional graphical user interfaces while offering two extra degrees of freedom in tasks where they are beneficial.