Touch behavior with different postures on soft smartphone keyboards

Text entry on smartphones is far slower and more error-prone than on traditional desktop keyboards, despite sophisticated detection and auto-correct algorithms. To strengthen the empirical and modeling foundation of smartphone text input improvements, we explore touch behavior on soft QWERTY keyboards when used with two thumbs, an index finger, and one thumb. We collected text entry data from 32 participants in a lab study and describe touch accuracy and precision for different keys. We found that distinct patterns exist for input among the three hand postures, suggesting that keyboards should adapt to different postures. We also discovered that participants' touch precision was relatively high given typical key dimensions, but there were pronounced and consistent touch offsets that can be leveraged by keyboard algorithms to correct errors. We identify patterns in our empirical findings and discuss implications for design and improvements of soft keyboards.