ExtendedThumb: a motion-based virtual thumb for improving one-handed target acquisition on touch-screen mobile devices

Screen size of mobile handheld devices such as cellular phones has been increasing, causing the decrease of thumb mobility. It is difficult for a user to hold a large touch-screen mobile device and reach a distant target on the screen with one hand. We propose ExtendedThumb, a virtual thumb proxy of the real thumb, to address this problem in single-handed interaction. ExtendedThumb reaches out to a distant target on a touch screen in the dragging direction of the real thumb but at a faster speed than the latter. Users can adjust the position of the virtual thumb by changing the dragging direction and distance of the real thumb. Results of an empirical evaluation show that ExtendedThumb significantly outperforms MagStick in speed and user satisfaction while achieving a similar accuracy. ExtendedThumb is also significantly better than the direct touch method in accuracy and user satisfaction. The findings provide insights into motion-based one-handed interaction with mobile devices.