Title: Glass+Skin: An Empirical Evaluation of the Added Value of Finger Identification to Basic Single-Touch Interaction on Touch Screens,
Abstract: The usability of small devices such as smartphones or interactive watches is
often hampered by the limited size of command vocabularies. This paper is an
attempt at better understanding how finger identification may help users invoke
commands on touch screens, even without recourse to multi-touch input. We
describe how finger identification can increase the size of input vocabularies
under the constraint of limited real estate, and we discuss some visual cues to
communicate this novel modality to novice users. We report a controlled
experiment that evaluated, over a large range of input-vocabulary sizes, the
efficiency of single-touch command selections with vs. without finger
identification. We analyzed the data not only in terms of traditional time and
error metrics, but also in terms of a throughput measure based on Shannon's
theory, which we show offers a synthetic and parsimonious account of users'
performance. The results show that the larger the input vocabulary needed by
the designer, the more promising the identification of individual fingers.