Performance Optimizations of Virtual Keyboards for Stroke-Based Text Entry on a Touch-Based Tabletop
Jochen Rick
Presented at UIST'10, October 3-6, 2010, New York, New York, USA
Author Bio
Jochen Rick was a research fellow at the United Kingdom's Open University, but now is a junior faculty member in the Department of Educational Technology at Saarland Universty. He holds a PhD in Computer Science from Georgia Tech. His primary interest is in how new media can enhance collaborative learning.
Summary
Hypothesis
Can two proposed alternative keyboard layouts reduce text entry times for stroke-based entry in comparison with tap-based entry?
Methods
Initially, participants completed a series of gestures both tapping and stroking through four points. The distance travelled and angles were measured. Sequences were drawn repetitively and in rapid succession. The results for the left-handed participants were flipped to resemble that of right-handed users. The author derived equations corresponding to times needed per gesture portion.
To test layouts, existing layouts were modified slightly so that they could be tested against a list of 40,000 of the most common English words. The results from this test were tested against the author's specialized layouts. Both tests measured the amount of time necessary to produce each word.
Results
Moving in a straight line took the least amount of time and changing angle by 180 degrees took the longest. More efficient angles follow arm direction, but the arm visually blocking was not a problem. The author's variation of Fitts' law had an increased coefficient of determination.
When comparing existing layouts, stroking was faster than tapping. Keyboards optimized for one-finger typing performed best. The author's generated square and hexagonal stroke keyboard layouts outperformed the tapped best of each of those categories.
Contents
For tabletop computing, tap-based virtual keyboards are not intended for ten-finger typing. Stroke-based keyboards address the lack of tactile feedback somewhat. The author produced two keyboard layouts that are statiscally more effecient than the standard Qwerty layout. Various other layouts exist, some of which address stroke-based entry. Shape writing matches the shape of the stroke as opposed to its absoluted position for word-based input. The ideal is a layout with letters frequently used in succession close to each other. Tap-based interfaces usually follow Fitts' law, which says that the time needed for a gesture follows a logarithmic function of distance over target width. The author sought to improve the approximation for time used to produce a gesture and used a variation of Fitts' law.
He created approximations for the length of time needed to produce a stroke or a series of taps. The approximations were applied to Project Gutenberg's 2006 list of most frequent English words. The author ignored special characters and capital letters, though characters with similar equivalents were mapped differently for strokes. An exhaustive search to produce the best keyboard layout is not feasible, so he used a simulated annealing process followed by hill climbing.
Discussion
The author sought to achieve a more efficient keyboard layout for stroking than current models. While the models he created are theoretically more efficient, his layout as it stands has ambiguity for word entry. Interpreting user input relies on software that guesses the correct input. This is such a significant step backwards from tapping that I cannot accept this model as a viable alternative for tapped layouts without substantial improvements.
My main problem with the stroked layouts is that they rely on predictions. These are difficult to generalize, as a person who only types in chatspeak requires a different subset of language from one who writes more formally. It would take a significant amount of work to produce efficient, and more importantly correct, predicting software.
The prediction software would be particularly interesting future work, though I'm not entirely convinced it would be feasible. If and only if it can be done, I could see myself using this keyboard layout.
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