Understanding One-Handed Thumb Interaction with a Mobile Touchscreen Device: Effects of Keyboard Size, Gap and Button Shape

Small, mobile touchscreen devices have increasingly permeated into our daily life over the last decade. However, interface design factors that are likely to influence input performance of the devices have not yet been fully investigated. The purpose of the current study was to explore the effects of keyboard size, gap and button shape on usability metrics in thumb interaction with a small, mobile touchscreen device. Twenty-eight volunteers attended a lab-based experiment where they were required to complete a series of letter input tasks with a touchscreen smartphone. The results indicated that keyboard size yielded significant effects on both accuracy rate and task completion time, and button shape and gap exerted significant influence on task completion time only. Interaction effects were observed between keyboard size and button shape on both accuracy rate and task completion time. Keyboard design factors that exerted optimal input performance were mostly preferred by users. Our findings have important implications and can help with the design of usable touchscreen interface, especially for small, mobile touchscreen devices.