  Mobile devices with touch keyboards have become ubiquitous, but text entry on
these devices remains slow and errorprone. Understanding touch patterns during
text entry could be useful in designing robust error-correction algorithms for
soft keyboards. In this paper, we present an analysis of text input behaviors
on a soft QWERTY keyboard in three different text entry postures: index finger
only, one thumb, and two thumb. Our work expands on the work of [1] by
considering the entire surface area of digit contact with the smartphone
keyboard, rather than interpreting each touch as a single point. To do this, we
captured touch areas for every key in a lab study with 8 participants and
calculated offsets, error rates, and size measurements. We then repeated the
original experiment described in [1] and showed that significant differences
exist when basing offset calculations on touch area compared to touch points
for two postures.
