keyboard. When the user’s finger or stylus moves on the
sensing keyboard, the stroke ink that moves in parallel is
displayed on the phantom keyboard that is not obscured
by the hand. However, such a design was in our experience
proven unnecessary after the first large-scale word-gesture
keyboard (Shape Writer WritingPad) release on the iPhone.
Most users quickly gained confidence, stopped worrying
about the letter underneath their fingertip, and realized they
only need to approximately cross the intended letters.
2. 4. Progression from ease to efficiency
One of the most important rationales of gesture keyboards
lies in facilitating transition from ease to efficiency.
Writing with a gesture keyboard is a mixture of two types
of behavior. The first type, used by beginners or for unfamiliar words, is letter-to-letter tracing. Such a process is visually
guided, closed-loop, and relatively slow. This visual recognition-based process is easy because it does not require any prior
memory. The second type, used by proficient users for
familiar words, is memory-driven gesturing. This process in
contrast is recall-driven, open-loop, efficient, and fast.
The two types of behavior are two ends of a continuum.
Our main behavioral theory of word shorthand gesture keyboards is that their use automatically shifts from the ease
end (visual tracing) to the efficient end (recall gesturing)
There are many factors facilitating such a shift. First, at
both ends of the continuum or anywhere in between, the
movement pattern is the same. The consistent movement
pattern for the same word helps the shift from visual trac-
ing to recall gesturing. On this point, we drew inspiration
in Kurtenbach and Buxton’s work on “marking menu”
design, 24 although a direct application of marking menus to
text input did not necessarily result in a successful text input
method. 40 With marking menus the user can either wait for
a visual radial menu to pop up, and then slide to the desired
slice, or make a gesture in the same direction without the
visual menu display if the angular gesture is remembered.
As observed by Kurtenbach and Buxton, 24 the consistent
movement patterns in the two distinct states of marking
menus facilitate novice to expert mode transition in mark-
ing menu use. The basic psychology literature on automatic-
ity in human behavior also shows that the key to developing
skilled, low attention, automatic behavior lies in consistent
mapping from stimuli to response. 35, 38
Figure 3. illustration: word-shorthand gesture keyboarding is expected to shift from primarily visual-guidance driven letter-to-letter tracing
to memory-recall driven gesturing.