SAN FRANCISCO JULY 22-26
Volume 19, Number 3, 1985
I s s u e s and T e c h n i q u e s in
T o u c h - S e n s i t i v e Tablet Input
William B u x t o n
R a l p h Hill
P e t e r Rowley
Computer Systems Research Institute
U n i v e r s i t y of T o r o n t o
Toronto, O n t a r i o
C a n a d a M5S 1A4
(416) 978-6320
1. Introduction
Abstract
Touch-sensitive tablets and their use in humanc o m p u t e r i n t e r a c t i o n a r e d i s c u s s e d , I t is s h o w n
that such devices have some important properties
that differentiate them from other input devices
(such as mice and joysticks). The analysis serves
t w o p u r p o s e s : (1) i t s h e d s l i g h t o n t o u c h t a b l e t s ,
a n d (2) i t d e m o n s t r a t e s h o w o t h e r d e v i c e s m i g h t b e
approached. Three specific distinctions between
touch tablets a n d one button mice are drawn. These
c o n c e r n t h e signaling of e v e n t s , m u l t i p l e p o i n t
s e n s i n g a n d t h e u s e of t e m p l a t e s . T h e s e d i s t i n c t i o n s a r e r e i n f o r c e d , a n d p o s s i b l e u s e s of t o u c h
tablets are illustrated, in an example application.
Potential enhancements to touch tablets and other
i n p u t d e v i c e s a r e d i s c u s s e d , as a r e s o m e i n h e r e n t
problems. The paper concludes with recommendations for future work.
CR C a t e g o r i e s a n d S u b j e c t D e s c r i p t o r s : 1.3.1 [ C o m p u t e r G r a p h i c s ] : H a r d w a r e A r c h i t e c t u r e : I n p u t Devi c e s . 1.3.6 [ C o m p u t e r G r a p h i c s ] : M e t h o d o l o g y a n d
Techniques: Device Independence, Ergonomics,
Interaction Techniques.
Increasingly, research in h u m a n - c o m p u t e r interaction is focusing on problems of input [Foley, Wallace
& C h a n 1984; Buxton 1983; Buxton £985]. M u c h of
this attention is directed towards input technologies. The ubiquitous Sholes keyboard is being
replaced and/or complemented by alternative technologies. For example, a major focus of the marketing strategy for two recent personal computers, the
Apple Macintosh and Hewlett-Packard 150, has been
on the input devices that they employ (the m o u s e
and touch-screen, respectively).
N o w that the range of available devices is expanding, how does one select the best technology for a
particular application? And once a technology is
chosen, hove can it be used most effectively? These
q u e s t i o n s a r e i m p o r t a n t , f o r a s B u x t o n [ 1983] h a s
a r g u e d , t h e w a y s i n w h i c h t h e u s e r physiccdty
interacts with an input device have a marked effect
o n t h e t y p e of u s e r i n t e r f a c e t h a t c a n b e e f f e c t i v e I y
supported.
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In t h e g e n e r a l s e n s e , t h e o b j e c t i v e of t h i s p a p e r is
to help in the selection process and assist in
e f f e c t i v e u s e of a s p e c i f i c c l a s s o:F d e v i c e s . O u r
a p p r o a c h is t o i n v e s t i g a t e a s p e c i f i c c l a s s of d e v i c e s : t o u c h - s e n s i t i v e t a b l e t s . We will i d e n t i f y t o u c h
tablets, enumerate their important properties, and
compare them to a more common input device, the
m o u s e . We t h e n g o o n t o g i v e e x a m p l e s of t r a n s a c tions where touch tablets can be used effectively.
There are two intended benefits for this approach.
F i r s t , t h e r e a d e r will a c q u i r e a n u n d e r s t a n d i n g of
t o u c h t a b l e t i s s u e s . S e c o n d , t h e r e a d e r will h a v e a
c o n c r e t e e x a m p l e of h o w t h e t e c h n o l o g y c a n b e
investigated, and can utilize the approach as a
m o d e l f o r i n v e s t i g a t i n g o t h e r c l a s s e s of d e v i c e s .
©
A t o u c h - s e n s i t i v e t a b l e t ( t o u c h t a b l e t f o r s h o r t ) is a
flat surface, usually mounted horizontally or nearly
h o r i z o n t a l l y , t h a t c a n s e n s e t h e l o c a t i o n of a f i n g e r
p r e s s i n g o n it. T h a t is, i t i s a t a b l e t t h a t c a n s e n s e
t h a t i t is b e i n g t o u c h e d , a n d w h e r e i t is b e i n g
General Terms: Design, Human Factors.
Additional Keywords and Phrases: touch sensitive
input devices.
2. T o u c h - S e n s i t i v e
1985 A C M 0 - 8 9 7 9 1 - 1 6 6 - 0 / 8 5 / 0 0 7 / 0 2 1 5 $ 0 0 . 7 5
Tablets
215
@ S I G G R A P H '85
touched. Touch tablets can vary greatly in size,
from a few inches on a side to several feet on a side.
T h e m o s t c r i t i c a l r e q u i r e m e n t is t h a t t h e u s e r is
not required point with some manually held device
s u c h as a s t y l u s o r p u c k .
What we have described in the previous paragraph
is a simple t o u c h t a b l e t . 0 n l y o n e p o i n t of c o n t a c t
is s e n s e d , a n d t h e n o n l y i n a b i n a r y , t o u c h / n o t o u c h ,
m o d e . O n e w a y t o e x t e n d t h e p o t e n t i a l of a s i m p l e
t o u c h t a b l e t is t o s e n s e t h e d e g r e e , o r p r e s s u r e , of
contact. Another is to sense multiple points of contact. In this case, the location (and possibly pressure) of several points of contact would be
reported. Most tablets currently on the m a r k e t are
of the "simple" variety. However, Lee, Buxton and
S m i t h [ 1985], a n d N a k a t a n i [ p r i v a t e c o m m u n i c a t i o n ] h a v e d e v e l o p e d p r o t o t y p e s of m u l t i - t o u c h ,
multi-pressure
sensing tablets.
We w i s h t o s t r e s s t h a t w e will r e s t r i c t o u r d i s c u s s i o n of t o u c h t e c h n o l o g i e s t o t o u c h t a b l e t s , w h i c h
can and should be used in ways that are different
from touch screens. Readers interested in touchscreen technology are referred to Herot & Weinsapf e l [1978], N a k a t a n i & R o h r l i c h [1983] a n d M i n s k y
[1984]. We a c k n o w l e d g e t h a t a f i a t t o u c h s c r e e n
m o u n t e d h o r i z o n t a l l y is a t o u c h t a b l e t as d e f i n e d
a b o v e . T h i s is n o t a c o n t r a d i c t i o n , a s a t o u c h s c r e e n
h a s e x a c t l y t h e p r o p e r t i e s of t o u c h t a b l e t s we
d e s c r i b e b e l o w , a s l o n g a s t h e r e is n o a t t e m p t t o
mount a display below (or behind) it or to make it
t h e c e n t e r of t h e u s e r ' s v i s u a l f o c u s .
S o m e s o u r c e s of t o u c h t a b l e t s a r e l i s t e d i n A p p e n d i x A.
3. P r o p e r t i e s
of Touch-Sensitive
T o u c h t a b l e t s h a v e a n u m b e r of p r o p e r t i e s
tinguish them from other devices:
that dis-
•
They have no mechanical
(such as stylus or puck).
in hostile environments
access terminals) where
ices can get lost, stolen,
•
Having no puck to slide or get bumped, the tracking symbol "stays put" once placed, thus making
them well suited for pointing tasks in environm e n t s s u b j e c t t o v i b r a t i o n o r m o t i o n (e.g., f a c tories, cockpits).
intermediate device
Hence they are useful
(e.g., c l a s s r o o m s , p u b l i c
such intermediate devor damaged.
They present no mechanical or kinesthetic restrictions on our ability to indicate more than one
p o i n t a t a t i m e . T h a t is, w e c a n u s e t w o h a n d s o r
more than one finger simultaneously on a single
tablet. (Remember, we can manually control at
216
•
Unlike joysticks and trackballs, they have a very
low p r o f i l e a n d c a n b e i n t e g r a t e d i n t o o t h e r
equipment such as desks and low-profile keyb o a r d s (e.g., t h e Key T r o n i c T o u c h P a d , s e e
A p p e n d i x A). T h i s h a s p o t e n t i a l b e n e f i t s i n p o r t able systems, and, according to the Keystroke
model of Card, Newell and M o r a n [19S0], reduces
homing time from the keyboard to the pointing
device.
•
They can be m o l d e d into one-piece constructions
thus eliminating cracks and grooves where dirt
can collect. This m a k e s t h e m well suited for very
clean environments (eg. hospitals) or very dirty
o n e s (eg., f a c t o r i e s ) .
•
Their simple construction, with no moving parts,
leads to reliable and long-lived operation, making
them suitable for environments where they will
be subjected to intense use or where reliability
is c r i t i c a l .
T h e y do, of c o u r s e , h a v e s o m e i n h e r e n t d i s a d v a n t a g e s , w h i c h will b e d i s c u s s e d a t t h e c l o s e of t h e
paper.
I n t h e n e x t s e c t i o n w e will m a k e t h r e e i m p o r t a n t
distinctions between touch tablets and mice. These
are:
•
Mice and touch tablets vary in the number and
t y p e s of e v e n t s t h a t t h e y c a n t r a n s m i t . T h e
d i f f e r e n c e is e s p e c i a l l y p r o n o u n c e d w h e n c o m paring to simple touch tablets.
•
Touch tablets can be made that can sense multip l e p o i n t s of c o n t a c t . T h e r e is n o a n a l o g o u s p r o perty for mice.
•
T h e s u r f a c e of a t a b l e t c a n b e p a r t i t i o n e d i n t o
r e g i o n s r e p r e s e n t i n g a c o l l e c t i o n of i n d e p e n d e n t
" v i r t u a l " d e v i c e s . T h i s is a n a l o g o u s t o t h e p a r t i t i o n i n g of a s c r e e n i n t o " w i n d o w s " o r v i r t u a l
d i s p l a y s . Mice, a n d o t h e r d e v i c e s t h a t t r a n s m i t
"'relative change" information, do not lend thems e l v e s t o t h i s m o d e of i n t e r a c t i o n w i t h o u t c o n suming display real estate for visual feedback.
With conventional tablets and touch tablets,
graphical, physical or virtual templates can be
placed over the input device to delimit regions.
This allows valuable screen real estate to be
preserved. Physical templates, when combined
with touch sensing, permit the operator to sense
the regions without diverting the eyes from the
primary display during visually demanding tasks.
Tablets
A s k i n g " W h i c h i n p u t d e v i c e is b e s t ? " i s m u c h l i k e
a s k i n g " H o w l o n g s h o u l d a p i e c e of s t r i n g b e ? " T h e
a n s w e r t o b o t h is: i t d e p e n d s o n w h a t y o u w a n t t o
use it for. With input devices, however, we are limi t e d i n o u r u n d e r s t a n d i n g of t h e r e l a t i o n s h i p
b e t w e e n d e v i c e p r o p e r t i e s a n d t h e d e m a n d s of a
s p e c i f i c a p p l i c a t i o n . We will i n v e s t i g a t e t o u c h
t a b l e t s f r o m t h e p e r s p e c t i v e of i m p r o v i n g o u r
u n d e r s t a n d i n g of t h i s r e l a t i o n s h i p . O u r c l a i m is
that other technologies warrant similar, or even
more detailed, investigation.
.
most two mice at a time: one in each hand. Given
t h a t w e h a v e t e n f i n g e r s , i t is c o n c e i v a b l e t h a t w e
may wish to indicate more than two points simult a n e o u s l y . A n e x a m p l e of s u c h a n a p p l i c a t i o n
appears below).
After these properties are discussed, a simple
f i n g e r p a i n t i n g p r o g r a m is u s e d t o i l l u s t r a t e t h e m
i n t h e c o n t e x t of a c o n c r e t e e x a m p l e . We w i s h t o
stress that we do not pretend that the program
represents a viable paint program or an optimal
i n t e r f a c e . I t is s i m p l y a v e h i c l e t o i l l u s t r a t e a
v a r i e t y of t r a n s a c t i o n s i n a n e a s i l y u n d e r s t a n d a b l e
context.
SAN FRANCISCO JULY 22-26
Volume 19, Number 3,1985
Finally, we discuss improvements
that must be
m a d e to c u r r e n t t o u c h t a b l e t t e c h n o l o g y , m a n y of
which we have demonstrated
in prototype form.
Also, we suggest potential improvements
to other
devices, motivated by our experience with touch
technology.
4. Three
Mice t
Distinctions
Between
Touch
Tablets
and
The distinctions we make in this section have to do
w i t h s u i t a b i l i t y of d e v i c e s f o r c e r t a i n t a s k s o r u s e
in certain configurations. W e a r e only interested in
showing that there are s o m e uses for which touch
tablets are not suitable, but other devices are, and
vice versa. W e m a k e no quantitative claims or c o m parisons regarding performance.
sible: the user may touch the tablet. This causes a
c h a n g e t o s t a t e 1. I n s t a t e 1, t h e u s e r is p r e s s i n g o n
the tablet, and as a consequence position reports
are sent to the host. There is no way to signal a
change to some other state, other than to release
( a s s u m i n g t h e e x c l u s i o n of t e m p o r a l o r s p a t i a l c u e s ,
which tend to be clumsy and difficult to learn). This
r e t u r n s t h e s y s t e m t o s t a t e 0. T h i s s i g n a l c o u l d n o t
be used to initiate rubber-banding,
~s i t c o u l d a l s o
mean that the user is pausing to think, or wishes to
initiate some other activity.
release
state I - contact
move
Signals
Consider a rubber-band line drawing task with a one
button mouse. The user would first position the
t r a c k i n g s y m b o l a t t h e d e s i r e d s t a r t i n g p o i n t of t h e
line by moving the mouse with the button released.
The button would then be depressed, to signal the
s t a r t of t h e l i n e , a n d t h e u s e r w o u l d m a n i p u l a t e t h e
line by moving the mouse until the desired length
a n d o r i e n t a t i o n w a s a c h i e v e d . T h e c o m p l e t i o n of t h e
line could then be signaled by releasing the buttonfi
Figure 1 is a state diagram that represents this
interface. Notice that the button press and release
a r e u s e d t o s i g n a l t h e b e g i n n i n g a n d e n d of t h e
rubber-band drawing task. Also note that in states
1 and 2 both motion and signaling (by pressing or
releasing the button, as appropriate) are possible.
release
{anchor, end}
sta.rt.tag point
~
point
state 1 - button up
state 2 - button down
F i g u r e l. S t a t e d i a g r a m f o r r u b b e r - b a n d i n g
a one-button mouse.
with
Now consider a simple touch tablet. It can be used
to position the tracking symbol at the starting
p o i n t of t h e l i n e , b u t i t c a n n o t g e n e r a t e t h e s i g n a l
needed to initiate rubber-banding.
Figure 2 is a
state diagram representation
of t h e c a p a b i l i t i e s of
a s i m p l e t o u c h t a b l e t . I n s t a t e 0, t h e r e i s n o c o n t a c t
w i t h t h e t a b l e t f l I n t h i s s t a t e o n l y o n e a c t i o n is p o s * A l t h o u g h w e are c o m p a r i n g t o u c h t a b l e t s to o n e b u t t o n m i c e t h r o u g h o u t t h i s s e c t i o n , m o s t of t h e c o m m e n t s
a p p l y e q u a l l y t o t a b l e t s w i t h o n e - b u t t o n p u c k s or ( w i t h
s o m e caveats) tablets with styli.
2 This a s s u m e s that the interface is designed so that
the button is held d o w n during drawing. Alternatively,
the button c a n b e released during drawing, a n d pressed
again, to signal the completion of the line.
S W e use state 0 to represent a state in w h i c h n o location. information is transmitted.
There n o analogous
state for mice, a n d h e n c e n o state 0 in the d i a g r a m s for
F i g u r e 2. D i a g r a m f o r s h o w i n g s t a t e s
simple touch-tablet.
of
T h i s i n a b i l i t y t o s i g n a l w h i l e p o i n t i n g is a s e v e r e
limitation with current touch tablets, that is,
tablets that do not report pressure in addition to
l o c a t i o n . ( I t is a l s o a p r o p e r t y of t r a c k b a l l s , a n d
joysticks without "fire" buttons). It renders them
unsuitable for use in many common interaction
t e c h n i q u e s f o r w h i c h m i c e a r e w e l l a d a p t e d (e.g.,
selecting and dragging objects into position,
rubber-band line drawing, and pop-up menu selection); techniques that are especially characteristic
of i n t e r f a c e s b a s e d o n L ~ r e e t Mc~r~ipulat£o~. [ S h n e i d e r m a n 198~].
O n e s o l u t i o n t o t h e p r o b l e m is t o u s e a s e p a r a t e
function button on the keyboard. However, this
usually means two-handed input where one could
d o , or, a w k w a r d c o - o r d i n a t i o n i n c o n t r o l l i n g t h e
button and pointing device with a single hand. An
alternative solution when using a touch tablet is to
p r o v i d e s o m e l e v e l of p r e s s u r e s e n s i n g . F o r e x a m p l e , if t h e t a b l e t c o u l d r e p o r t t w o l e v e l s of c o n t a c t
p r e s s u r e (i.e., h a r d a n d s o f t ) , t h e n t h e t r a n s i t i o n
from soft to hard pressure, and vice versa, could be
used for signaling. In effect, pressing hard is
equivalent to pressing the button on the mouse. The
state diagram showing the rubber-band line drawi n g t a s k w i t h t h i s f o r m of t o u c h t a b l e t is s h o w n i n
F i g u r e 3. 4
As a n a s i d e , u s i n g t h i s p r e s s u r e s e n s i n g s c h e m e
would permit us to select options from a menu, or
mice. With conventional tablets, this c o r r e s p o n d s to
"out of r a n g e " state.
At this point t h e a l e r t r e a d e r will wonder about difficulty
in distinguishing between h a r d and soft pressure, a n d
friction (especially when pressing hard). Taking the last
first, h a r d is a relative term. in p r a c t i c e friction need
n o t be a p r o b l e m (see I n h e r e n t Problems, below).
40ne would conjecture t h a t in the a b s e n c e of b u t t o n
clicks or o t h e r feedback, p r e s s u r e would be difficult to
regulate accurately. We have found two levels of press u r e to be easily distinguished, but this is a ripe a r e a for
research. For example, Stu Card [private communication] has suggested t h a t t h e t h r e s h o l d between soft and
h a r d should be reduced (become "'softer") while h a r d
p r e s s u r e is being maintained. This suggestion, and others, w a r r a n t formal experimentation.
217
S I G G R A P H '85
~igh~
release
state 0 - n o c o n t a c t
state I - l i g h t oontact
state 2 - 'hard' c o n t a c t
Multiple Virtual Devices and Templates
{anchor- e n d )
move
to select
startln9 F o n t
to select-
~
~
point
Figure 3. State diagram for rubber-banding with
pressure sensing touch tablet.
a c t i v a t e light b u t t o n s by positioning the t r a c k i n g
s y m b o l o v e r t h e i t e m a n d " p u s h i n g " . This is c o n s i s t e n t w i t h the g e s t u r e used with a mouse, and the
m o d e l of " p u s h i n g " b u t t o n s . With c u r r e n t s i m p l e
t o u c h t a b l e t s , one d o e s j u s t t h e o p p o s i t e : p o s i t i o n
o v e r t h e i t e m a n d t h e n l i f t off, or " p u l l " t h e b u t t o n .
F r o m t h e p e r s p e c t i v e of t h e s i g n a l s s e n t t o t h e h o s t
c o m p u t e r , t h i s t o u c h t a b l e t is c a p a b l e of d u p l i c a t ing t h e b e h a v i o u r of a o n e - b u t t o n m o u s e . This is n o t
t o s a y t h a t t h e s e d e v i c e s a r e e q u i v a l e n t or i n t e r c h a n g e a b l e . They a r e n o t . They a r e p h y s i c a l l y a n d
k i n e s t h e t i c a l l y v e r y d i f f e r e n t , a n d s h o u l d be u s e d i n
ways t h a t m a k e u s e of t h e u n i q u e p r o p e r t i e s of
each. F u r t h e r m o r e , such a t o u c h t a b l e t can gene r a t e one p a i r of s i g n a l s t h a t t h e o n e - b u t t o n m o u s e
c a n n o t -- s p e c i f i c a l l y , p r e s s a n d r e l e a s e ( t r a n s i t i o n
t o a n d f r o m s t a t e 0 in t h e a b o v e d i a g r a m s ) . T h e s e
s i g n a l s ( w h i c h a r e also a v a i l a b l e w i t h m a n y c o n v e n t i o n a l t a b l e t s ) a r e v e r y u s e f u l in i m p l e m e n t i n g c e r t a i n t y p e s of t r a n s a c t i o n s , s u c h as t h o s e b a s e d o n
character recognition.
An o b v i o u s e x t e n s i o n of t h e p r e s s u r e s e n s i n g conc e p t is t o allow c o n t i n u o u s p r e s s u r e s e n s i n g . T h a t
is, p r e s s u r e s e n s i n g w h e r e s o m e l a r g e n u m b e r of
d i f f e r e n t l e v e l s of p r e s s u r e m a y be r e p o r t e d . This
e x t e n d s t h e c a p a b i l i t y of t h e t o u c h t a b l e t b e y o n d
t h a t of a t r a d i t i o n a l o n e b u t t o n m o u s e . An e x a m p l e
of t h e u s e of t h i s f e a t u r e is p r e s e n t e d below.
Multiple P o s i t i o n S e n s i n g
With a t r a d i t i o n a l m o u s e or t a b l e t , only one p o s i t i o n
c a n b e r e p o r t e d p e r d e v i c e . One c a n i m a g i n e u s i n g
t w o m i c e or p o s s i b l y two t r a n s d u c e r s on a t a b l e t ,
b u t t h i s i n c r e a s e s c o s t s , a n d t w o is t h e p r a c t i c a l
l i m i t on t h e n u m b e r of m i c e or t a b l e t s t h a t c a n be
o p e r a t e d by a s i n g l e u s e r ( w i t h o u t u s i n g f e e t ) . Howe v e r , w h i l e we h a v e only t w o h a n d s , we h a v e t e n
f i n g e r s . As p l a y i n g t h e p i a n o i l l u s t r a t e s , t h e r e a r e
s o m e c o n t e x t s w h e r e we m i g h t w a n t t o u s e s e v e r a l ,
o r e v e n all of t h e m , a t o n c e .
T o u c h t a b l e t s n e e d n o t r e s t r i c t us i n t h i s r e g a r d .
G i v e n a l a r g e e n o u g h s u r f a c e of t h e a p p r o p r i a t e
t e c h n o l o g y , one c o u l d u s e all f i n g e r s of b o t h h a n d s
simultaneously, thus providing ten separate units
of i n p u t . Clearly, t h i s is w e l l b e y o n d t h e d e m a n d s of
m a n y a p p l i c a t i o n s a n d t h e c a p a c i t y of m a n y p e o p l e ,
however, there are exceptions. Examples include
c h o r d i n g on b u t t o n s or s w i t c h e s , o p e r a t i n g a s e t of
slide p o t e n t i o m e t e r s , and s i m p l e key r o l l - o v e r when
t o u c h t y p i n g . One e x a m p l e (using a s e t of s l i d e
p o t e n t i o m e t e r s ) will be i 1 1 u s t r a t e d below.
218
The power of m o d e r n graphics displays has been
enhanced by partitioning one physical display into a
n u m b e r of virtual displays. To support this, display
window managers have been developed. We claim
(see Brown, Buxton and Murtagh [ 1985]) that similar
benefits can be gained by developing an input window m a n a g e r that permits a single physical input
device to be partitioned into a n u m b e r of virtual
input devices, Furthermore, we claim that multitouch tablets are well suited to supporting this
approach.
Figure 4a shows a thick cardboard sheet that has
h o l e s c u t in s p e c i f i c p l a c e s . When i t is p l a c e d o v e r a
t o u c h t a b l e t as s h o w n in F i g u r e 4b, t h e u s e r is r e s t r i c t e d t o t o u c h i n g o n l y c e r t a i n p a r t s of t h e t a b l e t .
More i m p o r t a n t l y , t h e u s e r c a n f e e / t h e p a r t s t h a t
a r e t o u c h a b l e , a n d t h e i r s h a p e . E a c h of t h e " t o u c h able" regions represents a separate virtual device.
The d i s t i n c t i o n b e t w e e n t h i s t e m p l a t e a n d t r a d i t i o n a l t a b l e t m o u n t e d m e n u s ( s u c h as s e e n i n m a n y
CAD s y s t e m s ) is i m p o r t a n t .
T r a d i t i o n a l l y , t h e o p t i o n s h a v e been:
a) S a v e d i s p l a y r e a l e s t a t e b y m o u n t i n g t h e m e n u
on t h e t a b l e t s u r f a c e . The c o s t of t h i s o p t i o n is
eye d i v e r s i o n f r o m the display to the tablet, the
inability to " t o u c h type", and t i m e c o n s u m i n g
menu changes.
b) Avoid eye d i v e r s i o n by p l a c i n g t h e m e n u s on t h e
d i s p l a y . This a l s o m a k e i t e a s i e r t o c h a n g e
m e n u s , b u t s t i l l d o e s n o t allow " t o u c h t y p i n g " ,
and c o n s u m e s display space.
T o u c h t a b l e t s allow a n e w o p t i o n :
c) S a v e d i s p l a y s p a c e a n d a v o i d e y e d i v e r s i o n b y
u s i n g t e m p l a t e s t h a t c a n b e f e l t , a n d h e n c e , allow
" t o u c h t y p i n g " on a v a r i e t y of v i r t u a l i n p u t d e v i c e s . The c o s t of t h i s o p t i o n is t i m e c o n s u m i n g
menu (template) changes.
It m u s t b e r e m e m b e r e d t h a t f o r e a c h of t h e s e
o p t i o n s , t h e r e is a n a p p l i c a t i o n f o r w h i c h i t is b e s t .
We h a v e c o n t r i b u t e d a n ew o p t i o n , w h i c h m a k e s p o s s i b l e n e w i n t e r f a c e s . The n e w p o s s i b i l i t i e s i n c l u d e
more elaborate virtual devices because the
i m p r o v e d k i n e s t h e t i c f e e d b a c k allows t h e u s e r t o
c o n c e n t r a t e on p r o v i d i n g i n p u t , i n s t e a d of s t a y i n g
i n t h e a s s i g n e d r e g i o n . We will a l s o show (below)
t h a t its m a i n cost (time consuming m e n u changes)
can be reduced in s o m e applicatio~ts by eliminating
the templates.
5. E x a m p l e s o f T r a n s a c t i o n s Where T o u c h T a b l e t s
Can Be U s e d E f f e c t i v e l y
In o r d e r t o r e i n f o r c e t h e d i s t i n c t i o n s d i s c u s s e d i n
t h e p r e v i o u s s e c t i o n , a n d t o d e m o n s t r a t e t h e u s e of
t o u c h t a b l e t s , we will now w o r k t h r o u g h s o m e e x a m p l e s b a s e d on a t o y p a i n t s y s t e m . We w i s h t o s t r e s s
a g a i n t h a t we m a k e no c l a i m s a b o u t t h e q u a l i t y of
t h e e x a m p l e as a p a i n t s y s t e m . A p a i n t s y s t e m is a
c o m m o n and easily u n d e r s t o o d application, and
t h u s , we h a v e c h o s e n t o u s e it s i m p l y as a v e h i c l e
for discussing i n t e r a c t i o n t e c h n i q u e s t h a t use
touch tablets.
SAN FRANCISCO JULY 22"26
Volume 19, Number 3, 1985
F i g u r e 4a. S a m p l e t e m p l a t e .
F i g u r e 5. Main d i s p l a y for p a i n t p r o g r a m .
F i g u r e 4b. S a m p l e t e m p l a t e in use.
F i g u r e 6. Touch t a b l e t u s e d in d e m o n s t r a t i o n s .
The e x a m p l e p a i n t p r o g r a m allows t h e c r e a t i o n oI
s i m p l e f i n g e r p a i n t i n g s . The l a y o u t of t h e m a i n
d i s p l a y f o r t h e p r o g r a m is shown in F i g u r e 5. On t h e
l e f t is a l a r g e d r a w i n g a r e a w h e r e t h e u s e r c a n d r a w
s i m p l e t r e e - h a n d figures. On t h e r i g h t is a s e t of
m e n u i t e m s . When t h e l o w e s t i t e m is s e l e c t e d , t h e
u s e r e n t e r s a e o l a u r m i x i n g m o d e . In s w i t c h i n g to
t h i s m o d e , t h e u s e r is p r e s e n t e d w i t h a d i f f e r e n t
d i s p l a y t h a t is d i s c u s s e d below. The r e m a i n i n g
m e n u i t e m s a r e " p a i n t p o t s " . They a r e u s e d t o
s e l e c t t h e c o l o u r t h a t t h e u s e r will be p a i n t i n g with.
t h e p a i n t p r o g r a m d e s c r i b e d above, w h e r e t h e only
i n p u t d e v i c e is a t o u c h t a b l e t w i t h o u t p r e s s u r e
s e n s i n g . Menu s e l e c t i o n s c o u l d be m a d e b y p r e s s i n g
d o w n s o m e w h e r e in t h e m e n u a r e a , m o v i n g t h e
t r a c k i n g symbo] to the d e s i r e d m e n u i t e m and then
s e l e c t i n g by r e l e a s i n g . To p a i n t , t h e u s e r would
s i m p l y p r e s s down in t h e d r a w i n g a r e a and m o v e
( s e e F i g u r e 7 f o r a r e p r q s e n t a t i o n of t h e s i g n a l s
u s e d for p a i n t i n g w i t h t h i s p r o g r a m ) .
release
In e a c h of t h e f o l l o w i n g v e r s i o n s of t h e p r o g r a m , t h e
i n p u t r e q u i r e m e n t s a r e s l i g h t l y d i f f e r e n t . In all
c a s e s an 8 c m x 8 c m t o u c h t a b l e t is u s e d ( F i g u r e 6),
but the p r e s s u r e sensing r e q u i r e m e n t s vary. These
a r e n o t e d in e a c h d e m o n s t r a t i o n .
painti~
5.1. Painting Without P r e s s u r e S e n s i n g
This v e r s i o n of t h e p a i n t p r o g r a m i l l u s t r a t e s t h e
l i m i t a t i o n of h a v i n g no p r e s s u r e s e n s i n g . C o n s i d e r
F i g u r e 7. S t a t e d i a g r a m for d r a w i n g p o r t i o n
of s i m p l e p a i n t p r o g r a m .
219
S I G G R A P H '85
T h e r e a r e s e v e r a l p r o b l e m s w i t h t h i s p r o g r a m . The
m o s t o b v i o u s is in t r y i n g t o do d e t a i l e d d r a w i n g s .
The u s e r d o e s n o t k n o w w h e r e t h e p a i n t will a p p e a r
u n t i l i t a p p e a r s . This is l i k e l y t o be t o o l a t e . S o m e
f o r m of f e e d b a c k , t h a t s h o w s t h e u s e r w h e r e t h e
b r u s h is, w i t h o u t p a i n t i n g , is n e e d e d . U n f o r tunately, this cannot be done with this input device,
as i t is n o t p o s s i b l e to s i g n a l t h e c h a n g e f r o m t r a c k ing t o p a i n t i n g and v i c e v e r s a .
The s i m p l e s t s o l u t i o n t o t h i s p r o b l e m is t o u s e a
b u t t o n (e.g., a f u n c t i o n k e y on t h e k e y b o a r d ) to signal s t a t e c h a n g e s . The p r o b l e m w i t h t h i s s o l u t i o n is
t h e n e e d t o u s e t w o h a n d s on two d i f f e r e n t d e v i c e s
t o do one t a s k . This is a w k w a r d a n d r e q u i r e s p r a c tice to develop the c o - o r d i n a t i o n n e e d e d to m a k e
s m a l l r a p i d s t r o k e s in t h e p a i n t i n g . It is a l s o
i n e f f i c i e n t in its u s e of t w o h a n d s w h e r e one c o u l d
(and n o r m a l l y s h o u l d ) do.
A l t e r n a t i v e l y , a p p r o a c h e s u s i n g m u l t i p l e t a p s or
t i m i n g c u e s f o r s i g n a l l i n g c o u l d be t r i e d , h o w e v e r ,
we h a v e f o u n d t h a t t h e s e i n v a r i a b l y l e a d t o o t h e r
p r o b l e m s . It is b e t t e r t o find a d i r e c t s o l u t i o n u s i n g
t h e p r o p e r t i e s of t h e d e v i c e i t s e l f .
5.2. P a i n t i n g w i t h Two L e v e l s of P r e s s u r e
This v e r s i o n of t h e p r o g r a m u s e s a t a b l e t t h a t
r e p o r t s t w o l e v e l s of c o n t a c t p r e s s u r e t o p r o v i d e a
s a t i s f a c t o r y solution to the signaling p r o b l e m . A
low p r e s s u r e l e v e l (a l i g h t t o u c h by t h e u s e r ) is u s e d
f o r g e n e r a l t r a c k i n g . A h e a v i e r t o u c h is u s e d t o
m a k e m e n u s e l e c t i o n s , or t o e n a b l e p a i n t i n g ( s e e
Figure 8 for the t a b l e t s t a t e s used to control painting w i t h t h i s p r o g r a m ) . The two l e v e l s of c o n t a c t
p r e s s u r e allow us t o m a k e a s i m p l e b u t p r a c t i c a l
one f i n g e r p a i n t p r o g r a m .
move (to
starting point}
ties.
In t h i s t e c h n i q u e , we u t i l i z e a t a b l e t c a p a b l e of
s e n s i n g a c o n t i n u o u s r a n g e of t o u c h p r e s s u r e . With
t h i s a d d i t i o n a l signal, t h e u s e r c a n c o n t r o l b o t h t h e
w i d t h of t h e p a i n t t r a i l a n d i t s p a t h , u s i n g only o n e
finger. The new signal, p r e s s u r e , is u s e d t o c o n t r o l
w i d t h . This is a t e c h n i q u e t h a t c a n n o t b e u s e d w i t h
a n y m o u s e t h a t we a r e a w a r e of, a n d t o o u r
k n o w l e d g e , is a v a i l a b l e on o n l y o n e c o n v e n t i o n a l
t a b l e t ( t h e GTCO D i g i p a d w i t h p r e s s u r e p e n [GTCO
~9aa]).
We h a v e f o u n d t h a t u s i n g c u r r e n t p r e s s u r e s e n s i n g
tablets, the user can a c c u r a t e l y supply two to t h r e e
b i t s of p r e s s u r e i n f o r m a t i o n , a f t e r a b o u t 15
m i n u t e s p r a c t i c e . This is s u f f i c i e n t f o r s i m p l e doodling a n d m a n y o t h e r a p p l i c a t i o n s , b u t i m p r o v e d
p r e s s u r e r e s o l u t i o n is r e q u i r e d f o r h i g h q u a l i t y
painting.
5.4. "Windows" on the Tablet: Colour Selection
We now d e m o n s t r a t e how t h e s u r f a c e of t h e t o u c h
t a b l e t c a n be dyTzarnieally p a r t i t i o n e d i n t o "'wind o w s " o n t o v i r t u a l i n p u t d e v i c e s . We u s e t h e s a m e
b a s i c t e c h n i q u e s as d i s c u s s e d u n d e r t e m p l a t e s
( a b o v e ) , b u t show how t o u s e t h e m w i t h o u t t e m p l a t e s . We do t h i s in t h e c o n t e x t of a e o l o u r s e l e c t i o n m o d u l e for o u r p a i n t p r o g r a m . This m o d u l e
i n t r o d u c e s a n e w d i s p l a y , s h o w n in F i g u r e 9.
move while
painting
Figure 8. State d i a g r a m for painting portion of
simple paint p r o g r a m using pressure
sensing touch tablet.
This v e r s i o n is v e r y m u c h l i k e u s i n g t h e one b u t t o n
m o u s e on t h e Apple M a c i n t o s h w i t h M a c P a i n t [Willia m s , 1984]. Thus, a s i m p l e t o u c h t a b l e t is n o t v e r y
u s e f u l , b u t one t h a t r e p o r t s t w o l e v e l s of p r e s s u r e
is s i m i l a r i n p o w e r ( b u t n o t f e e l or a p p l i c a b i l i t y ) t o
a one b u t t o n m o u s e . 5
5.3. P a i n t i n g w i t h C o n t i n u o u s P r e s s u r e S e n s i n g
In t h e p r e v i o u s d e m o n s t r a t i o n s , we h a v e only i m p l e mented interaction techniques that are common
u s i n g e x i s t i n g t e c h n o l o g y . We now i n t r o d u c e a t e c h nique that provides functionality beyond that
obtainable using most conventional input technolos Also,there is the problem of friction,to be discussed
below under "Inherent Problems".
220
F i g u r e 9. C o l o u r ' m i x i n g d i s p l a y .
In t h i s d i s p l a y , t h e l a r g e l e f t s i d e c o n s i s t s of a
c o l o u r p a t c h s u r r o u n d e d by a n e u t r a l g r e y b o r d e r .
This is t h e p a t c h of c o l o u r t h e u s e r is w o r k i n g on.
The r i g h t s i d e of t h e d i s p l a y c o n t a i n s t h r e e b a r
g r a p h s w i t h two l i g h t b u t t o n s u n d e r n e a t h . The p r i m a r y f u n c t i o n of t h e b a r g r a p h s is t o p r o v i d e f e e d b a c k , r e p r e s e n t i n g r e l a t i v e p r o p o r t i o n s of r e d ,
g r e e n a n d b l u e in t h e c o l o u r p a t c h . Along w i t h t h e
l i g h t b u t t o n s below, t h e y a l s o s e r v e t o r e m i n d t h e
u s e r of t h e c u r r e n t l a y o u t of t h e t o u c h t a b l e t .
In t h i s m o d u l e , t h e t o u c h t a b l e t is u s e d as a " ' v i r t u a l
o p e r a t i n g c o n s o l e " . Its l a y o u t is s h o w n (to s c a l e ) i n
F i g u r e 10. T h e r e a r e 3 v a l u a t o r s ( c o r r e s p o n d i n g t o
t h e b a r g r a p h s on t h e s c r e e n ) u s e d t o c o n t r o l
SAN FRANCISCO JULY 22-26
Volume 19, Number 3, 1985
c o l o u r , a n d tw o b u t t o n s : one, on t h e r i g h t , t o b r i n g
up a p o p - u p m e n u u s e d t o s e l e c t t h e c o l o u r to be
m o d i f i e d , a n d a n o t h e r , on t h e l e f t , t o e x i t .
•
......
"-~3
i
of t h e p a t c h .
valuators
-
-
~ " / / 8 c m x 8 cm
tablet
surface
F i g u r e 11. I n c r e a s i n g r e d c o n t e n t , by p r e s s i n g on
r e d v a l u a t o r a n d s l i d i n g up.
F i g u r e 10. L a y o u t of v i r t u a l d e v i c e s on t o u c h t a b l e t .
The s i n g l e m o s t i m p o r t a n t p o i n t t o be m a d e i n t h i s
e x a m p l e is t h a t a s i n g l e physica2 d e v i c e is b e i n g
u s e d t o i m p l e m e n t 5 v i r t u a l d e v i c e s (3 v a l u a t o r s
an d 2 b u t t o n s ) . This is a n a l o g o u s t o t h e u s e of a
d i s p l a y w i n d o w s y s t e m , i n i t s goals, a n d i t s i m p l e mentation.
The s e c o n d m a i n p o i n t is t h a t t h e r e is n o t h i n g on
t h e t a b l e t t o d e l i m i t t h e r e g i o n s . This d i f f e r s f r o m
t h e u s e of p h y s i c a l t e m p l a t e s as p r e v i o u s l y disc u s s e d , an d s h o w s how, in t h e a b s e n c e of t h e n e e d
fo r a p h y s i c a l t e m p l a t e , we c a n i n s t a n t l y c h a n g e t h e
" w i n d o w s " on t h e t a b l e t , w i t h o u t s a c r i f i c i n g t h e
ability to touch type.
We h a v e f o u n d t h a t w h e n t h e t a b l e t s u r f a c e is s m a l l ,
an d t h e p o r t i o n i n g of t h e s u r f a c e s is n o t t o o c o m plex, t h e u s e r s v e r y q u i c k l y ( t y p i c a l l y i n o n e or t w o
m i n u t e s ) l e a r n t h e p o s i t i o n s of t h e v i r t u a l d e v i c e s
r e l a t i v e t o t h e e d g e s of t h e t a b l e t . More i m p o r tantly, they can use the virtual devices, practically
error free, without diverting attention from the
display. (We h a v e r e p e a t e d l y o b s e r v e d t h i s
b e h a v i o u r in t h e u s e of a n a p p l i c a t i o n t h a t u s e s a l0
c m s q u a r e t a b l e t t h a t is d i v i d e d i n t o 3 s l i d e r s w i t h a
s i n g l e b u t t o n a c r o s s t h e top).
B e c a u s e no t e m p l a t e is n e e d e d , t h e r e is no n e e d f o r
the user to pause to change a template when entering t h e e o l o u r m i x i n g m o d u l e . Also, at no p o i n t is
the u s e r ' s a t t e n t i o n d i v e r t e d f r o m the display.
T h e s e a d v a n t a g e s c a n n o t be a c h i e v e d w i t h an y o t h e r
d e v i c e we k n o w of, w i t h o u t c o n s u m i n g d i s p l a y r e a l
estate.
The e o l o u r of t h e c o l o u r p a t c h is m a n i p u l a t e d by
dTagg£r~g t h e r e d , g r e e n a n d b l u e v a l u e s up a n d
down w i t h t h e v a l u a t o r s on t h e t o u c h t a b l e t . The
v a l u a t o r s a r e i m p l e m e n t e d in r e l a t i v e m o d e (i.e.,
t h e y a r e s e n s i t i v e t o c h a n g e s in p o s i t i o n , n o t a b s o l u t e p o s i t i o n ) , a n d a r e m a n i p u l a t e d l i k e one d i m e n sional mice. For example, to m a k e the p a t c h m o r e
r e d , t h e u s e r p r e s s e s n e a r t h e l e f t s i d e of t h e
t a b l e t , about half way to the top, and slides the
f i n g e r up ( s e e F i g u r e i i). F o r l a r g e r c h a n g e s , t h e
device can be r e p e a t e d l y s t r o k e d ( m u c h like stroking a m o u s e ) . F e e d b a c k is p r o v i d e d by c h a n g i n g t h e
l e v e l in t h e b a r g r a p h on t h e s c r e e n a n d t h e c o l o u r
Using a mouse, the above i n t e r a c t i o n could be
a p p r o x i m a t e d by p l a c i n g t h e t r a c k i n g s y m b o l o v e r
t h e b a r s of c o l o u r , a n d d r a g g i n g t h e m up or down.
H o w e v e r , if t h e b a r s a r e n a r r o w , t h i s t a k e s a c u i t y
an d c o n c e n t r a t i o n t h a t d i s t r a c t s a t t e n t i o n f r o m t h e
p r i m a r y t a s k -- m o n i t o r i n g t h e c o l o u r of t h e p a t c h .
Furthermore, note that the touch tablet implement a t i o n d o e s n o t n e e d t h e b a r s t o be d i s p l a y e d a t all,
t h e y a r e only a c o n v e n i e n c e t o t h e u s e r . T h e r e a r e
i n t e r f a c e s w h e r e , in t h e i n t e r e s t s of m a x i m i z i n g
a v a i l a b l e d i s p l a y a r e a , t h e r e will be no i t e m s on t h e
d i s p l a y a n a l o g o u s t o t h e s e b a r s . T h a t is, t h e r e
w o u l d be n o t h i n g on t h e d i s p l a y t o s u p p o r t an
i n t e r a c t i o n t e c h n i q u e t h a t allows v a l u e s t o be m a n i p u l a t e d by a m o u s e .
Finally, we c a n t a k e t h e e x a m p l e o n e s t e p f u r t h e r by
i n t r o d u c i n g t h e u s e of a t o u c h t a b l e t t h a t c a n s e n s e
m u l t i p l e p o i n t s of c o n t a c t (e.g., [Lee, e t el. 1985]).
With t h i s t e c h n o l o g y , all t h r e e c o l o u r v a l u e s c o u l d
be c h a n g e d a t t h e s a m e t i m e (for e x a m p l e , f a d i n g t o
b l a c k by d r a w i n g all t h r e e s l i d e r s d o w n t o g e t h e r
w i t h t h r e e f i n g e r s of o n e hand). This s i m u l t a n e o u s
a d j u s t m e n t of c o l o u r s c o u l d n o t b e s u p p o r t e d by a
m o u s e , n o r an y s i n g l e c o m m e r c i a l l y a v a i l a b l e i n p u t
d e v i c e we know of. C o n t r o l l i n g s e v e r a l v a l u a t o r s
w i t h o n e h a n d is c o m m o n i n m a n y o p e r a t i n g consoles, for example: s t u d i o light control, audio
m i x e r s , an d t h r o t t l e s f o r m u l t i - e n g i n e v e h i c l e s (e.g.,
a i r c r a f t an d b o a t s ) . H e n c e , t h i s e x a m p l e d e m o n s t r a t e s a cost effective m e t h o d for providing funct i o n a l i t y t h a t is c u r r e n t l y u n a v a i l a b l e (or a v a i l a b l e
only a t g r e a t c o s t , in t h e f o r m of a c u s t o m f a b r i c a t e d console), b u t has wide applicability.
5.5. Szlmmary of Examples
T h r o u g h t h e s e s i m p l e e x a m p l e s , we h a v e d e m o n strated several things:
*
The a b i l i t y t o s e n s e a t l e a s t t w o l e v e l s of p r e s s u r e is a v i r t u a l n e c e s s i t y f o r t o u c h t a b l e t s , as
w i t h o u t it, a u x i l i a r y d e v i c e s m u s t be u s e d f or
signaling, and " d i r e c t m a n i p u l a t i o n " i n t e r f a c e s
c a n n o t be e f f e c t i v e l y s u p p o r t e d .
•
The e x t e n s i o n t o c o n t i n u o u s p r e s s u r e s e n s i n g
o p e n s up n ew p o s s i b i l i t i e s i n h u m a n - c o m p u t e r
interaction.
221
@ S I G G R A P H '85
•
•
T ou ch t a b l e t s a r e s u p e r i o r to m i c e a n d t a b l e t s
w h e n m a n y s i m p l e d e v i c e s a r e t o be s i m u l a t e d .
This is b e c a u s e : (a) t h e r e is no n e e d f o r a
mechanical intermediary between the fingers
a nd t h e t a b l e t s u r f a c e , (b) t h e y allow t h e u s e of
t e m p l a t e s ( i n c l u d i n g t h e e d g e s of t h e t a b l e t ,
w h i c h is a t r i v i a l b u t u s e f u l t e m p l a t e ) , a n d (e)
t h e r e is no n e e d f o r p o s i t i o n a l f e e d b a c k t h a t
would consume valuable display space.
The a b i l i t y t o s e n s e m u l t i p l e p o i n t s of c o n t a c t
r a d i c a l l y c h a n g e s t h e w a y in w h i c h u s e r s m a y
i n t e r a c t w i t h t h e s y s t e m . The c o n c e p t of m u l t i p l e p o i n t s of c o n t a c t d o e s n o t e x i s t for, n o r is i t
a p p l i c a b l e to, c u r r e n t c o m m e r c i a l l y a v a i l a b l e
m i c e an d t a b l e t s .
6. I n h e r e n t P r o b l e m s w i t h T o u c h T a b l e t s
A p r o b l e m w i t h t o u c h t a b l e t s t h a t is a n n o y i n g in t h e
long t e r m is f r i c t i o n b e t w e e n t h e u s e r ' s f i n g e r and
t h e t a b l e t s u r f a c e . This c a n be a p a r t i c u l a r l y s e v e r e
p r o b l e m if a p r e s s u r e s e n s i t i v e t a b l e t is u s e d , a n d
t h e u s e r m u s t m a k e long m o t i o n s a t h i g h p r e s s u r e .
This p r o b l e m c a n b e a l l e v i a t e d by c a r e f u l s e l e c t i o n
of m a t e r i a l s an d c a r e i n t h e f a b r i c a t i o n and c a l i b r a t i o n of t h e t a b l e t , e Also, t h e u s e r i n t e r f a c e c a n b e
d e s i g n e d to a v o i d e x t e n d e d p e r i o d s of h i g h p r e s sure.
P e r h a p s t h e m o s t difficult p r o b l e m is p r o v i d i n g
g o o d f e e d b a c k to t h e u s e r w h e n u s i n g t o u c h t a b l e t s .
F o r e x a m p l e , if a s e t of p u s h - o n / p u s h - o f f b u t t o n s
a r e b e i n g s i m u l a t e d , t h e t r a d i t i o n a l f o r m s of f e e d b a c k ( i l l u m i n a t e d b u t t o n s or d i f f e r e n t b u t t o n
h e i g h t s ) c a n n o t be u s e d . Also, b u t t o n s a n d o t h e r
c o n t r o l s i m p l e m e n t e d on t o u c h t a b l e t s l a c k t h e
k i n e s t h e t i c feel a s s o c i a t e d with real switches and
k n o b s . As a r e s u l t , u s e r s m u s t be m o r e a t t e n t i v e t o
visual and audio feedback, and i n t e r f a c e designers
m u s t be f r e e r in p r o v i d i n g t h i s f e e d b a c k . (As an
e x a m p l e of how t h i s m i g h t b e e n c o u r a g e d , t h e i n p u t
"window manager" could automatically provide
a u d i b l e c l i c k s as f e e d b a c k f o r b u t t o n p r e s s e s ) .
7. P o t e n t i a l E n h a n c e m e n t s
to Touch Tablets (and
other devices)
The f i r s t p r o b l e m t h a t one n o t i c e s w h e n u s i n g t o u c h
t a b l e t s is " j i t t e r " w h e n t h e f i n g e r is r e m o v e d f r o m
t h e t a b l e t . T h a t is, t h e l a s t few l o c a t i o n s r e p o r t e d
b y t h e t a b l e t , b e f o r e i t s e n s e s loss of c o n t a c t , t e n d
t o be v e r y u n r e l i a b l e .
This p r o b l e m c a n b e e l i m i n a t e d by m o d i f y i n g t h e
f i r m w a r e of t h e t o u c h t a b l e t c o n t r o l l e r so t h a t i t
k e e p s a s h o r t FIF0 q u e u e of t h e s a m p l e s t h a t h a v e
m o s t r e c e n t l y be s e n t to t h e h o s t . When t h e u s e r
r e l e a s e s p r e s s u r e , t h e o l d e s t s a m p l e is r e t r a n s m i t t e d , an d t h e q u e u e is e m p t i e d . The l e n g t h
of t h e q u e u e d e p e n d s on t h e p r o p e r t i e s of t h e t o u c h
t a b l e t (e.g., s e n s i t i v i t y , s a m p l i n g r a t e ) . We h a v e
found that determining a suitable value requires
e As a bad example, one commercial "touch" tablet requires so much pressure for reliable sensing that the
finger cannot be smoothly dragged across the surface.
Instead, a wooden or plastic stylus must be used, thus
loosing many of the advantages of touch sensing.
222
o n l y a f ew m i n u t e s of e x p e r i m e n t a t i o n .
A r e l a t e d p r o b l e m with m o s t c u r r e n t t a b l e t cont r o l l e r s ( n o t j u s t t o u c h t a b l e t s ) is t h a t t h e y do n o t
i n f o r m the host c o m p u t e r when the u s e r has ceased
p r e s s i n g on t h e t a b l e t (or m o v e d t h e p u c k o u t of
r a n g e ) . This i n f o r m a t i o n is e s s e n t i a l t o t h e d e v e l o p m e n t of c e r t a i n t y p e s of i n t e r f a c e s . (As a l r e a d y
m e n t i o n e d , t h i s s i g n a l is n o t a v a i l a b l e f r o m m i c e ) .
C u r r e n t l y , one is r e d u c e d t o d e d u c i n g t h i s e v e n t b y
t i m i n g t h e i n t e r v a l b e t w e e n s a m p l e s s e n t by t h e
tablet. Since the tablet controller can easily determ i n e w h e n p r e s s u r e is r e m o v e d (and m u s t if i t is t o
a p p l y a d e - j i t t e r i n g a l g o r i t h m as a b o v e ) , i t s h o u l d
share this information with the host.
Clearly, p r e s s u r e s e n s i n g is an a r e a o p e n t o
d e v e l o p m e n t . Two p r e s s u r e s e n s i t i v e t a b l e t s h a v e
b e e n d e v e l o p e d a t t h e U n i v e r s i t y of T o r o n t o [ S a s a k i ,
e t al. 1981; Lee, e t al. 1985]. One h a s b e e n u s e d t o
d e v e l o p s e v e r a l e x p e r i m e n t a l i n t e r f a c e s an d w a s
f o u n d t o be a v e r y p o w e r f u l tool. They h a v e r e c e n t l y
b e c o m e a v a i l a b l e f r o m E l o g r a p h i c s an d Big B r i a r
( s e e A p p e n d i x A). P r e s s u r e s e n s i n g is n o t o n l y f o r
t o u c h t a b l e t s . Mice, t a b l e t p u c k s a n d s t y l i c o u l d all
benefit by a u g m e n t i n g switches with s t r a i n gauges,
or o t h e r p r e s s u r e s e n s i n g i n s t r u m e n t s . GTCO, f o r
example, manufactures a stylus with a pressure
s e n s i n g t i p [GTCO 1982], a n d t h i s , l i k e o u r p r e s s u r e
s e n s i n g t o u c h t a b l e t s , h as p r o v e n v e r y u s e f u l .
8. C o n c l u s i o n s
We h a v e s h o w n t h a t t h e r e a r e e n v i r o n m e n t s f o r
which some devices are better adapted than others.
In p a r t i c u l a r , t o u c h t a b l e t s h a v e a d v a n t a g e s in
m a n y h o s t i l e e n v i r o n m e n t s . F o r t h i s r e a s o n , we
suggest t h a t t h e r e are e n v i r o n m e n t s and applications w h e r e touch t a b l e t s m a y be the m o s t
appropriate input technology.
This b e i n g t h e c a s e , we h a v e e n u m e r a t e d t h r e e
m a j o r d i s t i n c t i o n s b e t w e e n t o u c h t a b l e t s a n d one
b u t t o n mice (although similar distinctions exist for
m u l t i - b u t t o n mice and conventional tablets). These
a s s i s t in i d e n t i f y i n g e n v i r o n m e n t s a n d a p p l i c a t i o n s
w h e r e touch t a b l e t s would be m o s t a p p r o p r i a t e .
These distinctions concern:
•
l i m i t a t i o n in t h e a b i l i t y t o s i g n a l e v e n t s ,
•
s u i t a b i l i t y for m u l t i p l e point sensing, and
•
t h e a p p l i c a b i l i t y of t a c t i l e t e m p l a t e s .
These distinctions have been r e i n f o r c e d , and s o m e
s u g g e s t i o n s on how t o u c h t a b l e t s m a y be u s e d h a v e
b e e n g i v e n , by d i s c u s s i n g a s i m p l e u s e r i n t e r f a c e .
F r o m t h i s e x a m p l e , an d t h e d i s c u s s i o n of t h e dist i n c t i o n s , we h a v e i d e n t i f i e d s o m e e n h a n c e m e n t s
t h a t can be m a d e to t o u c h t a b l e t s and o t h e r input
d e v i c e s . The m o s t i m p o r t a n t of t h e s e a r e p r e s s u r e
s e n s i n g a n d t h e a b i l i t y t o s e n s e m u l t i p l e p o i n t s of
contact.
We h o p e t h a t t h i s p a p e r m o t i v a t e s i n t e r f a c e
d e s i g n e r s t o c o n s i d e r t h e u s e of t o u c h t a b l e t s a n d
sh o w s s o m e ways t o u s e t h e m e f f e c t i v e l y . Also, we
h o p e i t e n c o u r a g e s d e s i g n e r s a n d m a n u f a c t u r e r s of
input devices to develop and m a r k e t input devices
w i t h t h e e n h a n c e m e n t s t h a t we h a v e d i s c u s s e d .
SAN FRANCISCO JULY 22-26
The c h a l l e n g e f o r t h e f u t u r e is t o d e v e l o p t o u c h
tablets that sense continuous pressure at multiple
p o i n t s of c o n t a c t a n d i n c o r p o r a t e t h e m i n p r a c t i c a l
i n t e r f a c e s . We b e l i e v e t h a t we h a v e s h o w n t h a t t h i s
is w o r t h w h i l e a n d h a v e s h o w n s o m e p r a c t i c a l w a y s
to use touch tablets. However, interface designers
m u s t s t i l l do a g r e a t d e a l of w o r k t o d e t e r m i n e
w h e r e a m o u s e is b e t t e r t h a n a t o u c h t a b l e t a n d
vice versa.
F i n a l l y , we h a v e i l l u s t r a t e d , b y e x a m p l e , a n
a p p r o a c h t o t h e s t u d y of i n p u t d e v i c e s , s u m m a r i z e d
b y t h e c r e d o : " K n o w t h e i n t e r a c t i o n s a d e v i c e is
i n t e n d e d t o p a r t i c i p a t e in, a n d t h e s t r e n g t h s a n d
w e a k n e s s e s of t h e d e v i c e . " This a p p r o a c h s t r e s s e s
t h a t t h e r e is no s u c h t h i n g as a " g o o d i n p u t d e v i c e , "
only good i n t e r a c t i o n t a s k / d e v i c e c o m b i n a t i o n s .
9. Acknowledgements
The s u p p o r t of t h i s r e s e a r c h b y t h e N a t u r a l S c i e n c e s a n d E n g i n e e r i n g R e s e a r c h C o u n c i l of C a n a d a
is g r a t e f u l l y a c k n o w l e d g e d . We a r e i n d e b t e d t o
K e v i n M u r t a g h a n d Ed B r o w n f o r t h e i r w o r k o n v i r t u a l i n p u t d e v i c e s a n d w i n d o w i n g on i n p u t . Also, we
are indebted to Elographics Corporation for having
s u p p l i e d u s w i t h t h e - h a r d w a r e o n w h i c h s o m e of t h e
underlying studies are based.
We w o u l d l i k e t o t h a n k t h e r e f e r e e s w h o p r o v i d e d
many useful comments that have helped us with the
presentation.
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A Multi-Touch T h r e e Dimensional T o u c h S e n s i t i v e Tablet. Human Factors i n
CoMputer Systems: pp. 21-25. (CHI'85
C o n f e r e n c e P r o c e e d i n g s , April 14-18,
1985, San F r a n s i s c o ) .
Minsky, M.R.
Jul 1984
Manipulating S i m u l a t e d Objects w i t h
R e a l - w o r l d G e s t u r e s using a F o r c e a n d
P o s i t i o n Sensitive Screen. CoTrt/ruter
Graphics 18.3: pp. 195-203. (SIGGRAPH'84 C o n f e r e n c e P r o c e e d i n g s , July
23-27, 1984, Minneapolis, Minnesota).
Nakatani, L.H.
Rohrlieh, J.A.
Dec 1983
S o f t Machines: A P h i l o s o p h y of U s e r C o m p u t e r I n t e r f a c e Design. H u m a n Factors i,n Computing 2~jstems: pp. 19-23.
(CHI'83 C o n f e r e n c e P r o c e d i n g s ,
D e c e m b e r 12-15, 1983, Boston>.
Sets aki, L.
Fedorkow, G.
Buxton, W.
R e t t e r a t h , C.
Smith, K.C.
1981
A T o u c h S e n s i t i v e I n p u t Device.
}:~'oceedings o f the 5th trttern~t'~onal
Conference on CovrLputer Mus/,c. N o r t h
Texas S t a t e University, Denton Texas,
N o v e m b e r 1981.
S h n e i d e r m a n . B.Direct Manipulation: A S t e p B e y o n d P r o Aug 1983
g r a m m i n g Languages. Computer 16.8:
pp. 57-69.
Williams, G.
Feb 1984
The Apple M a c i n t o s h Computer. Byte 9.2:
pp. 30-54.
Appendix k T o u c h T a b l e t S o u r c e s
Big Briar: 3 by 3 i n c h c o n t i n u o u s p r e s s u r e sensing t o u c h
tabiet
Big Briar, Inc.
Leicester, NC
28748
Chalk B o a r d Inc.: "Power Pad", l a r g e t o u c h t a b l e for
micro-computers
Chalk Board Inc.
3772 P l e a s a n t d a l e Rd.,
Atlanta, GA 30340
Elographics: v a r i o u s s i z e s of t o u c h t a b l e t s , including
p r e s s u r e sensing
Elographics, Inc.
105 Randolph Toad
Oak Ridge, T e n n e s s e e
37830
(515)-48Z-4100
223
@
Key T r o n i c : K e y b o a r d w i t h t o u c h pad.
Keytronic
P.O. Box 14687
S p o k a n e , WA 99214
(5o9)-92s-sooo
K o a l a P a d T e c h n o l o g i e s : Approx. 5 b y 7 i n c h t o u c h t a b l e t
for micro-computers
Koala T e c h n o l o g i e s
3100 P a t r i c k H e n r y Drive
S a n t a Clara, C a l i f o r n i a
95050
Spiral Systems: Trazor Touch Panel, 3 by 3 inch touch
tablet
Spiral System I n s t r u m e n t s , Inc.
4853 CordelI Avenue, Suite A-10
Bethesda. Maryland
20814
TASA: 4 b y 4 i n c h t o u c h t a b l e t ( r e l a t i v e s e n s i n g only)
T o u c h A c t i v a t e d S w i t c h A r r a y s Inc.
1270 L a w r e n c e Sin. Road. S u i t e G
Sunnyvale. California
94089
224
SIG
GR
AP
H '85