A Comparison of Consecutive and
Concurrent Input Text entry
Techniques for Mobile Phones
Daniel Wigdor & Ravin Balakrishnan
Text Messaging
• Estimated 500,000,000,000 text messages
in 2003 worldwide
• More popular outside North America
2
Ambiguity
• Pressing “2” : {2,a,b,c,A,B,C}
3
Problem
• Multiple selection actions required
• MacKenzie & Soukoreff:
• Between group selection: {2,a,b,c,A,B,C}
• Within group selection: {a}
4
Consecutive Selection
• Most prior techniques consecutive:
• First make between group selection
• Then make within group selection, or
disambiguation of automatic selection
• MultiTap, T9, 2-Key, LetterWise,
WordWise…
• What about selecting concurrently?
5
Concurrent Selection: TiltText
•
•
•
•
•
Presented at UIST 2003
Between-group selection: press key
Within-group selection: tilt phone
Actions performed concurrently
Suggests new area of research
6
Taxonomy: Multiplexed Keypad
Single Key
Multiple Keys
Single Press Multi Press
Single Press Multi Press
Consecutive
#1
MultiTap
Linguistic,
Two-key
#4
Concurrent
TiltText
(with tilt
sensor)
#2
#3
#5
• 1,2 not possible
• 4 & 5 are regressive
• 3 suggests a use for chording
7
Mobile Chording
• Chording input for mobile devices:
• Selection tasks suggests better fit for
chording on mobile phone
8
ChordTap
• Mobile phone selection tasks:
• Between group selection (phone keypad)
• Within group selection (chord keys)
• Performed concurrently
9
Design Issues
• Mapping chord states to within-group
selection
• Event that triggers text generation
10
Chord Mappings
• Ignoring case, buttons have 4 or 5
characters
• Each chord has 2 states (down=0, up=1)
• log25 = 3, 3 chords needed
11
Chord Mappings
Chord
States
Character
Selected
Example
000
Numeral
7
001
First letter
p
010
Second letter
q
100
Third letter
r
011
Fourth letter
s
101
Fourth letter
s
110
Fourth letter
s
111
Fourth letter
s
12
Character Generation Event
• Issue: when is character generated?
• Actions To Generate a Character:
1.
Depress
keypad button
2.
Depress
chord Key
3.
Release…
which?
13
Why Does it Matter?
• Non-event keys can be visualized
• Reduces erroneous text entry
• Helps with learning
• Non-event key can be held for
subsequent character, savings
14
Keypad Button Release (eg):
1.
Depress
keypad button:
2. Depress chord key:
Screen: 9
3.
W
X
Y
Z
Release keypad button – text is generated.
If next character requires same chord, keep
it held down to skip step 2.
15
Work Savings
• Subsequent characters with same chords:
000
001
010
100
110
2
A
B
C
-
3
D
E
F
-
4
G
H
I
-
5
J
K
L
-
6
M
N
O
-
7
P
Q
R
S
8
T
U
V
-
9
W
X
Y
Z
16
Keypad Button Release
• Allows for visualization of withingroup selection
• Allows same chord to be held for
successive characters
• Savings on 20% of pairings
17
Chord Key Release (eg):
1.
Depress
chord key:
2. Depress keypad button:
…
Screen: A
3.
D
G
J
…
Release chord key – text is generated.
If next character requires same chord, keep
it held down to skip step 2.
18
Work Savings
• Subsequent characters with same keypad
button:
2
A
B
C
-
3
D
E
F
-
4
G
H
I
-
5
J
K
L
-
6
M
N
O
-
7
P
Q
R
S
8
T
U
V
-
9
W
X
Y
Z
19
Chord-Key Release
• Character generated when chord-key
released
• Allows for visualization of betweengroup selection
• Allows same button to be held for
successive characters
• Savings on 9% of pairings
20
Chord-Key or Keypad Button
• Text generated every time any key
released
• Allows for no pre-visualization
• Greatest savings: 29%
21
Our Prototype
• Button release text
generation
• Equipped with 3 chords
• Implemented on Mot i95cl
• Mouse board for chords
• 2-handed
22
The Study
• Comparing ChordTap to MultiTap
• Between-Subject Design:
15 participants
3 techniques (MultiTap: 1 or 2 handed, ChordTap)
16 blocks of 20 phrases each
2 sessions
• Same phrases for both techniques
• Measured time & accuracy
• Participants told to correct mistakes
23
Results: Overall Speed
End of experiment: MT1: 11.05, MT2: 12.04, CT: 16.06
20
One-Handed MT
Two-Handed MT
ChordTap
18
16
14
12
`
10
8
Day 1
Day 2
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
6
1
Text Entry Speed (WPM)
•
Block
24
Power-Law Extrapolation
20
16
y = 7.7391x0.1466
R2 = 0.7964
14
12
`
10
y = 8.0351x0.1195
R2 = 0.9032
8
6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Text Entry Speed (WPM)
18
y = 8.4133x0.2411
R2 = 0.9479
One-Handed MT
Two-Handed MT
ChordTap
Block
25
Results: Error Rate
8
One-Handed MT
Two-Handed MT
ChordTap
7
Error rate (%)
6
5
4
3
2
1
Day 1
Day 2
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
Block
26
Conclusions
• Identified taxonomy of research
• Explored a new area within taxonomy
• Fit chording to mobile-phone keypad:
• Mappings
• Text generation event
• Implemented prototype
• Formal study conducted
• Chording better than MultiTap
27
Future Work
• Chording for one hand
• Further exploration of taxonomy
• Study of text generation event and
mappings
28
Acknowledgements
•
•
•
•
•
•
Tovi Grossman
Maya Przybylski
Krista Strickland
DGP Lab members
Study participants
Microsoft Research
29
Thank You!
30