A study of two-handed scrolling and selection on standard notebook computers.

Although two-handed input can improve both efficiency and quality of user interaction, it is not commonly adopted as it requires additional input devices. In this paper we propose two-handed interaction on standard hardware - notebooks with external mouse - and for a common task - 2D scrolling. We introduce four techniques that leverage the built-in touchpad as a dedicated scrolling device for the non-dominant hand, for scenarios in which the mouse is used in parallel for object selection and manipulation tasks. The techniques implement relative scrolling, flicking, absolute positioning and token-based input on the touchpad. We present an empirical evaluation of these techniques in a task that simulates activities such as retouching of photos, or interaction with maps, in which users often switch between mouse interaction and scrolling. The results show initially best performance with relative scrolling as a familiar mapping, but strong learning effects for all techniques. Users had difficulty with absolute mapping of touchpad input due to a tendency to clutching and finger repositioning, but we observed that these problems are compensated when a token is used as absolute input device.