Multilingual Touchscreen Keyboard Design and Optimization

English words were tested in random order. Participants were asked to tap each word
repeatedly ten times in a row (Trial T1 to T10) to reach the expert input speed. In case of
a mistake, the user had to click a button to clear it and repeat the word. The 19 words
were:
the and you that is in of know not they get have were are bit quick fox jumps lazy
Adopted from (Zhai & Kristensson, 2008), these words cover all letters in English
so together they touch on every letter key in a keyboard. Furthermore they have a high
correlation in letter frequency with the spoken American National Corpus (R2 = 0.88) so
they are representative in letter coverage. Note again the purpose of this experiment was
not to demonstrate users’ ability to learn an optimized layout for realistic typing tasks,
which had been demonstrated before. The purpose was rather to test the Fitts-digraph
model’s precision, particularly as applied to the new K5 layout and the traditional
QWERTY layout. For this purpose, these 19 words should give sufficient and diverse test
samples since these words involve very different letter transitions.
Design
A within-subjects design with repeated measures was employed. The independent
variables were two touchscreen keyboard layouts (K5 and QWERTY) and 19 English
words. Each participant performed the repeated tapping tasks on both of the two layouts,
with order of appearance balanced using a Latin Square.
Prior to performing the tasks, participants tapped one English word that was not
included in the experimental word list to familiarize themselves with the experimental
procedure. During the study, they were instructed to perform the task as quickly as
possible and as accurately as possible. Breaks were enforced between changes of
touchscreen keyboard layouts.
Measures
The dependent variable is completion time, defined as the time from the moment the
first letter of the targeted word is tapped until the last letter of the targeted word is tapped.
We focused on the interval between the first and the last letter to verify the Fitts-digraph
model used in our optimization process.
4.2 Results
The percentage of erroneous trials was between 0.3% and 4% for any word on any
layout. The mean word completion time on each keyboard is shown in Figure 11.
24