A Comparison of Consecutive and Concurrent Input Text entry Techniques for Mobile Phones

Daniel Wigdor & Ravin Balakrishnan

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Text Messaging• Estimated 500,000,000,000 text messages

in 2003 worldwide

• More popular outside North America

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Ambiguity• Pressing “2” : {2,a,b,c,A,B,C}

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Problem• Multiple selection actions required• MacKenzie & Soukoreff:

• Between group selection: {2,a,b,c,A,B,C}• Within group selection: {a}

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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?

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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

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Taxonomy: Multiplexed KeypadSingle 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

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Mobile Chording• Chording input for mobile devices:

• Selection tasks suggests better fit for chording on mobile phone

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ChordTap• Mobile phone selection tasks:

• Between group selection (phone keypad)• Within group selection (chord keys)

• Performed concurrently

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Design Issues• Mapping chord states to within-group

selection• Event that triggers text generation

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Chord Mappings• Ignoring case, buttons have 4 or 5

characters• Each chord has 2 states (down=0, up=1)• log25 = 3, 3 chords needed

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Chord MappingsChord 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

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Character Generation Event• Issue: when is character generated?• Actions To Generate a Character:Depresskeypad button

Depresschord Key1. 2. 3. Release…

which?

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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

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Keypad Button Release (eg):1. Depress

keypad button:2. Depress chord key:

Screen: 9 W X Y Z

3. Release keypad button – text is generated.If next character requires same chord, keepit held down to skip step 2.

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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

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Keypad Button Release• Allows for visualization of within-

group selection• Allows same chord to be held for

successive characters• Savings on 20% of pairings

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Chord Key Release (eg):1. Depress

chord key:2. Depress keypad button:

3. Release chord key – text is generated.If next character requires same chord, keepit held down to skip step 2.

Screen: A D G J …

…

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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

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Chord-Key Release• Character generated when chord-key

released• Allows for visualization of between-

group selection• Allows same button to be held for

successive characters• Savings on 9% of pairings

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Chord-Key or Keypad Button• Text generated every time any key

released• Allows for no pre-visualization• Greatest savings: 29%

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Our Prototype• Button release text

generation• Equipped with 3 chords• Implemented on Mot i95cl• Mouse board for chords• 2-handed

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The Study• Comparing ChordTap to MultiTap• Between-Subject Design:

15 participants3 techniques (MultiTap: 1 or 2 handed, ChordTap)16 blocks of 20 phrases each2 sessions

• Same phrases for both techniques• Measured time & accuracy• Participants told to correct mistakes

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Results: Overall Speed• End of experiment: MT1: 11.05, MT2: 12.04, CT: 16.06

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Block

Text

Ent

ry S

peed

(WP

M)

One-Handed MTTwo-Handed MTChordTap

`

Day 1 Day 2

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Power-Law Extrapolation

y = 8.0351x0.1195

R2 = 0.9032

y = 7.7391x0.1466

R2 = 0.7964

y = 8.4133x0.2411

R2 = 0.9479

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10

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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

Block

Tex

t Ent

ry S

peed

(W

PM

)

One-Handed MTTwo-Handed MTChordTap

`

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Results: Error Rate

0

1

2

3

4

5

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7

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Block

Err

or r

ate

(%)

One-Handed MTTwo-Handed MTChordTap

Day 1 Day 2

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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

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Future Work• Chording for one hand• Further exploration of taxonomy• Study of text generation event and

mappings

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Acknowledgements• Tovi Grossman• Maya Przybylski• Krista Strickland• DGP Lab members• Study participants• Microsoft Research

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Thank You!