Paper Reading #7: Performance Optimizations of Virtual Keyboards for Stroke-Based Text Entry on a Touch-Based Tabletop

Reference Information

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 is currently a faculty member in the Department of Educational Technology at Saarland University.  He holds a PhD in Computer Science from Georgia Tech and spent 3 years as a research fellow at the Open University working on the ShareIT project.

Summary

Hypothesis

Keyboard layout plays a large role in the effectiveness of shape-writing, or stroke-based text 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

After applying his mathematical model to a number of existing layouts, he found that wide-set keyboard layouts like Dvorak and Qwerty performed very poorly as swipe-text entry.  As he pointed out, however, this is to be expected as they were designed with a very different usage in mind.  On the other hand, he presented two optimized layouts, Hexagon OSK and Square OSK, which were markedly faster than their already-existing counterparts. 

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

With the user generally standing up or looking down at the surface, there might be some issues with the design. Physical keyboards are impractical, and the QWERTY keyboard layout is inefficient, since the hands cannot be rested on the surface to type. So this alternative was a good start.