Improving Two-Thumb Text Entry on Touchscreen Devices

Abstract

We study the design of split keyboards for fast text entry with two thumbs on mobile touchscreen devices. The layout of KALQ was determined through first studying how users should grip a device with two hands. We then assigned letters to keys computationally, using a model of two-thumb tapping. KALQ minimizes thumb travel distance and maximizes alternation between thumbs. An error-correction algorithm was added to help address linguistic and motor errors. Users reached a rate of 37 words per minute (with a 5% error rate) after a training program.

What is KALQ?

KALQ is a split keyboard for touchscreen devices. The position of the keyboard on the display and the assignment of letters to keyslots were informed by a series of studies conducted with the aim of maximizing typing performance. KALQ is used by gripping the device from its corners. Trained users achieved an entry rate of 37 wpm (5% error rate). This is an improvement of 34% over their baseline performance with a standard touch-QWERTY system. This rate is the highest ever reported for two-thumb typing on a touchscreen device. The following factors are exploited in the design of KALQ:
  1. Grip: Grasping the tablet with its corner in the “valley” created by the thenar and hypothenar eminence yields ~4% faster tapping performance than does a random grip. Moreover, the associated keyboard layout occludes the display the least.
  2. Hover-over technique: When typing with two thumbs, the idle thumb should not stay put but approach its next target and hover over it to minimize travel distance. We estimate that this typing strategy saves about 10–20% on MT in alternating taps. See an image here.
  3. Optimization of letter assignment: KALQ was optimized computationally from a model of best-performance two-thumb typing. As a result, it maximizes alternating taps and minimizes same side travel distances. Our model predicted a benefit of 4% over a comparable quasi-QWERTY layout. However, this prediction was made assuming the same typing technique and grip. Without the technique and grip, the benefit will be larger.
  4. Error correction: We developed an error-correction technique that adapts well-known techniques to the unique motor and linguistic aspects of two-thumb typing. Although our users’ error rates were not improved by the online version of our corrector, offline analyses showed that with better parameters, the error rate can be decreased by 1.3 percentage points.

What is special about the layout?

The layout has the following properties:
  1. The division of work is almost equal, at 54% and 46% for the right and left thumb, respectively.
  2. Alternation is rapid: 62% of the taps are switches.
  3. Travel distances are short: On average, the left thumb moves 86 px, the right 117.
  4. The spacebars are centrally located.
  5. The right thumb handles all vowels except y. The clustering of vowels around the spacebar favors quick switches and minimizes travel distance. The right thumb is responsible for 64% of same-side taps.
  6. The left thumb has most of the consonants, exploiting its ability to hover above the next button sooner. It has most first letters of words and most of the consonants.
Is it difficult to learn? Yes and no. Yes in the sense that it will take about 8 hours of practice to reach the typing rate that is comparable to that of a regular Qwerty keyboard on the same device. Practice beyond that point will improve the rate further. No in the relative sense: learning for eaxmple the ten-finger typing technique for physical keyboards takes about 20-30 hours of practice.

Download KALQ

We are currently working hard to release the KALQ keyboard for Android-based devices (smartphones and tablets) in early May 2013. The release will allow replacing the in-built keyboard with KALQ. The release will include instructions on how to practice use. Please follow this page for updates. The released version will have the following features
  • Full character set
  • Easy calibration to user's hand size
  • Version for left handed users
  • Training program (later in 2013)
  • Layouts optimized for different languages (later in 2013)


Authors: Antti Oulasvirta, Anna Reichel, Wenbin Li, Yan Zhang, Myroslav Bachynskyi, Keith Vertanen, Per Ola Kristensson

Source and full text:
http://www.mpi-inf.mpg.de/~oantti/KALQ/

 

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