Designing finger orientation input for mobile touchscreens

A large number of today's systems use interactive touch surfaces as the main input channel. Current devices reduce the richness of touch input to two-dimensional positions on the screen. A growing body of work develops methods that enrich touch input to provide additional degrees of freedom for touch interaction. In particular, previous work proposed to use the finger's orientation as additional input. To efficiently implement new input techniques which make use of the new input dimensions, we need to understand the limitations of the input. Therefore, we conducted a study to derive the ergonomic constraints for using finger orientation as additional input in a two-handed smartphone scenario. We show that for both hands, the comfort and the non-comfort zone depend on how the user interacts with a touch surface. For two-handed smart-phone scenarios, the range is 33.3% larger than for tabletop scenarios. We further show that the phone orientation correlates with the finger orientation. Finger orientations which are harder to perform result in phone orientations where the screen does not directly face the user.