ExtendedThumb: A Target Acquisition Approach for One-Handed Interaction With Touch-Screen Mobile Phones

In this paper, we propose ExtendedThumb, a virtual thumb proxy of a real thumb, to address the target selection problem caused by decreased thumb mobility in single-handed interaction. ExtendedThumb moves in the same direction as a real thumb with a longer moving distance on a touch screen. Users can adjust the direction of the virtual thumb by changing the dragging direction of the real thumb. The selection of a target is achieved by lifting the real thumb up from the screen when a red cross at the tip of the virtual thumb is placed on the target. The unique design of ExtendedThumb addresses common visual occlusion and low accuracy problems in one-handed interaction. We conducted an empirical user evaluation of ExtendedThumb with 36 participants who were asked to hold a mobile phone and click on targets with only one hand using three target acquisition methods, including direct touch, MagStick, and ExtendedThumb. Task completion time and error rates were analyzed using a 3 × 2 repeated measures analysis of variance with factors of target acquisition methods and target size. Bonferroni post-hoc tests were carried out for multiple comparisons. ExtendedThumb significantly outperforms MagStick in target acquisition speed, perceived ease of use, perceived effectiveness, and overall satisfaction, while achieving a similar level of accuracy. ExtendedThumb also achieves significantly higher accuracy, perceived ease of use, perceived effectiveness, and overall satisfaction than direct touch. The findings provide both research and practical insights for one-handed interaction with mobile devices.