ATOMIK and other stylus keyboards

One method of mobile text input is tapping on graphical on-screen keyboards with a stylus. ShapeWriter enables one to write sokgraphs (shorthand on keyboard as graphs) on these graphical keyboards to reach a much higher level of speed and more enjoyable text writing experience.

The most commonly used graphical keyboards have a QWERTY layout, invented by Christopher Sholes, Carlos Glidden, and Samuel W. Soule in 1868 for the purpose of minimizing mechanical jamming. QWERTY was so arranged that many adjacent letter pairs (digraphs) appear on the opposite sides of the keyboard. Contrary to popular belief, this design in fact is good for two handed typing, because it also facilitates alternation of the left and right hand. When used as a stylus keyboard, however, it means the stylus has to travel back and forth more frequently and over longer distance than necessary.

Another way to arrange a stylus keyboard is strictly alphabetical along one dimension. Novice users can find keys easily in this layout. The eventual efficiency of such a layout, however, is also poor.

QWERTY as a stylus keyboard

A strictly alphabetical layout for ease of locating keys initially

ATOMIK (Alphabetically Tuned and Optimized Mobile Interface Keyboard) is a graphical keyboard optimized with the following three features.

First, ATOMIK has higher movement efficiency for tapping movement than other stylus keyboards. This was designed by a Metropolis optimization algorithm in which the keyboard was treated as a "molecule" and each key as an "atom". The "atomic" interactions among all of the keys drove the movement cost – defined by the summation of all Fitts' law movement times between every pair of keys, weighted by the statistical frequency of the corresponding pair of letters in English – towards the minimum.

Second, the layout was alphabetically tuned. There is a general tendency that letters from A to Z run from the upper left corner to the lower right corner of the keyboard. This gives novice users a cue to look for letters that are not yet memorized.

The original ATOMIK tapping keyboard. Hexagonal keys maximizes the area for tapping action

ATOMIK layout revised for ShapeWriter

Third, it maximizes, without sacrificing the first two features, the letter connectivity of the most common words. Many common words or comment fragments of words, such as "the" and "ing" are totally connected.

Stylus tapping points on each key tend to form a 2D Gaussian distribution. Keys in a stylus keyboard hence should be circular. Hexagon keys approximate circles but can still pack without gaps.

When shape writing on a graphical keyboard, the shape of the keys is irrelevant. We therefore used square keys in the revised ATOMIK layout for ShapeWriter. The most frequently used key in stylus tapping, the space key, is no longer as frequently needed and is moved out of the core layout. We also swapped D and K so ED and ING, two common word endings, are more separated.

The shape writing approach we later developed is superior to stylus keyboarding. However if one really wants to stay with the "chicken head motion" of tapping on graphical keyboard, some of the principles in ShapeWriter can be applied to relax the precision requirement of tapping inside every key. Based on a lexicon, an Elastic Stylus Keyboard (ESK) can automatically correct the mis-tapped keys by matching the geometric pattern the user taps against the correct word templates and give the user the word intended.

More technical information, together with literature review on the topics covered in this page, can be found in the following papers:

Zhai, S., Hunter, M., Smith, B.A., Performance Optimization of Virtual Keyboards, Human-Computer Interaction, Vol 17 (2&3). pp 229-269. 2002.
Kristensson, P-O.and Zhai, S. Relaxing Stylus Typing Precision by Geometric Pattern Matching. Proc. IUI 2005—ACM Conference on Intelligent User Interfaces 2005, pp. 151–158, ACM Press.
Smith, B.A., Zhai, S. Optimised Virtual Keyboards with and without Alphabetical Ordering - A Novice User Study, in Proc. of INTERACT 2001: Eighth IFIP Conference On Human-Computer Interaction, Tokyo, Japan, July 9-13, pp 92-99.
Lee, P., Zhai, S. Top-down learning strategies: can they facilitate stylus keyboard learning? International Journal of Human-Computer Studies, Vol. 60 (5&6) pp. 585-598. 2004.
Zhai, S., Hunter, M., Smith, B.A., The Metropolis Keyboard -- An Exploration of Quantitative Techniques for Virtual Keyboard Design, in the Proceeding of the 13th Annual ACM Symposium on User Interface Software and Technology (UIST 2000), November 5-8, 2000, San Diego, California. pp 119-128.

Research Contacts: Shumin Zhai, Barton A Smith