ForceRay: Extending Thumb Reach on Mobile Touch Devices Using Force Input

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Christian Corsten, Marcel Lahaye, Jan Borchers, and Simon Voelker
To appear in Proceedings of CHI'19 ACM, 212:1 - 212:12

Smartphones are used predominantly one-handed, using the thumb for input. Many smartphones, however, have grown beyond 5″. Users cannot tap everywhere on these screens without destabilizing their grip. ForceRay lets users aim at an out-of-reach target by applying a force touch at a comfortable thumb location, casting a virtual ray towards the target. Varying pressure moves a cursor along the ray. When reaching the target, quickly lifting the thumb selects it. In a first study, ForceRay was 195 ms slower and had a 3% higher selection error than the best existing technique, BezelCursor, but ForceRay caused significantly less device movement than all other techniques, letting users maintain a steady device grip and removing their concerns about device drops. A second study demonstrated that an hour of training speeds up both BezelCursor and ForceRay, and that both are equally fast for targets at the screen border.