Text entry has been a bottleneck of nontraditional computing devices. One of the promising methods is the virtual keyboard for touch screens. Correcting previous estimates on virtual keyboard efficiency in the literature, we estimated the potential performance of the existing Qwerty, FITALY, and OPTI designs of virtual keyboards to be in the neighborhood of 28, 36, and 38 words per minute (wpm), respectively. This article presents 2 quantitative design techniques to search for virtual keyboard layouts. The first technique simulated the dynamics of a keyboard with digraph springs between keys, which produced a Hooke keyboard with 41.6 wpm movement efficiency. The second technique used a Metropolis random walk algorithm guided by a "Fitts-digraph energy" objective function that quantifies the movement efficiency of a virtual keyboard. This method produced various Metropolis keyboards with different shapes and structures with approximately 42.5 wpm movement efficiency, which was 50% higher than Qwerty and 10% higher than OPTI. With a small reduction (41.16 wpm) of movement efficiency, we introduced 2 more design objectives that produced the ATOMIK layout. One was alphabetical tuning that placed the keys with a tendency from A to Z so a novice user could more easily locate the keys. The other was word connectivity enhancement so the most frequent words were easier to find, remember, and type.

Built upon the Fitts' law and digraph model developed by MacKenzie and colleague [2, 3], we introduce two physics-based methods to graphical keyboard design. One method uses physical simulation of digraph springs and the other uses the Metropolis method. Both methods produced keyboard layouts comparable to or better than existing best designs by manual trial and error methods. We also corrected an error in previous predictions and concluded that the upper bound performance of a graphical keyboard should be at 40 to 44 wpm. The effect of varying key size and the use of multiple space keys are discussed.

Text entry user interfaces have been a bottleneck of non traditional computing devices. One of the promising methods is the virtual keyboard on touch screens. Various layouts have been manually designed to replace the dominant QWERTY layout. This paper presents two computerized quantitative design techniques to search for the optimal virtual keyboard. The first technique simulated the dynamics of a keyboard with “digraph springs” between keys, which produced a “Hooke’s” keyboard with 41.6 wpm performance. The second technique used a Metropolis random walk algorithm guided by a “Fitts energy” objective function, which produced a “Metropolis” keyboard with 43.1 wpm performance. The paper also models and evaluates the perfo rmance of four existing keyboard layouts. We corrected erroneous estimates in the literature and predicted the performance of QWERTY, CHUBON, FITALY, OPTI to be in the neighborhood of 30, 33, 36 and 38 wpm respectively. Our best design was 40% faster than QWERTY and 10% faster than OPTI, illustrating the advantage of quantitative user interface design techniques based on models of human performance over traditional trial and error designs guided by heuristics.