One-handed thumb interaction of mobile devices from the input accuracy perspective

Abstract

One-handed thumb interaction has been widely used for mobile devices with touch screens. This study investigated input accuracy and pressing patterns of one-handed thumb interaction by conducting an experiment with forty subjects. The experiment examined seventy-five different touch key designs, combinations of three touch key sizes (i.e., squares with 4 mm, 7 mm, and 10 mm widths) and twenty-five touch key locations. Two accuracy measures, success rate and input offset, were collected in the experiment. The results showed that success rate increased with target size. Touch key locations providing a high success rate (‘accurate region’) were identified for each touch key size, and they differed depending on touch key size. Input offset, the difference between the center of a target and a pressed point, was also affected by touch key size and location, and its distribution had a similar form to the Gaussian distribution. The results regarding input offset provided a basic understanding of pressing patterns of one-handed thumb interaction. Furthermore, a practical approach for designing usable touch keys was proposed to improve success rate of one-handed interaction. A computer simulation was performed to validate the approach using the data collected in the experiment. The proposed approach could increase input accuracy of one-handed interaction without an increase of task completion time. Relevance to industry One-handed thumb interaction with a small touch screen has been widely accepted in the handset industry. This study is an initial attempt to systematically investigate input accuracy and pressing patterns of one-handed thumb interaction. In addition, the proposed solution to usable touch key design has advantages over previous techniques from the UI designer’s perspective as well as from the user’s perspective. Hence, the results of this study could be widely used in the design of usable touch interfaces for mobile devices, especially mobile phones.