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Precise Selection Techniques for Multi-
Touch Screens
Hrvoje BenkoAndy D. Wilson
Patrick Baudisch
Columbia University and Microsoft ResearchCHI 2006
CHI 2006 2
Selecting a small target is very HARD!
CHI 2006 3
Small target size comparison Average finger ~ 15 mm wide
TargetUI element
Width(abstract screen)
Width17” screen1024x768
Width 30” screen1024x768
Close button 18 pixels
6 mm(40% of finger)
10.8 mm(66% of finger)
Resize handle 4 pixels
1.34 mm(9% of finger)
2.4 mm(16% of finger)
CHI 2006 4
Touchscreen Issues
1. Finger >>> Target2. Finger occludes the target3. Fingers/hands shake and jitter4. Tracking can be noisy (e.g. video) 5. No hover state (hover == drag)
CHI 2006 5
Previous Work
Solutions based on single touch interfaces and complex on-screen widgets:
Albinsson, P. A. and Zhai, S. “High Precision Touch Screen Interaction.” (CHI ’03)
Sears, A. and Shneiderman, B. “High Precision Touchscreens: Design Strategies and Comparisons with a Mouse.” (’91)
CHI 2006 6
Dual Finger Selections
Multi-touch techniques Single fluid interaction
no lifting/repositioning of fingers Design guidelines:
Keep simple things simple. Provide an offset to the cursor when so
desired. Enable user controlled control-display
ratio.
CHI 2006 7
Simulating Hover State
Extension of the “area==pressure” idea (MacKenzie and Oniszczak, CHI 1998)
Problem: LARGE area difference reliable clicking SMALL movement (i.e. SMALL area
difference) precise and accurate clicking
CHI 2006 8
SimPress (Simulated Pressure)
Clicking gesture – “finger rocking”
Goal: Maximize ∆ touch
area Minimize ∆ cursor
location
CHI 2006 9
Top Middle Cursor
Large ∆ touch area Small ∆ cursor loc.
Center-of-Mass Cursor
Large ∆ touch area Large ∆ cursor loc.
SimPress Cursor Placement
CHI 2006 10
SimPress in Action
CHI 2006 11
Dual Finger Selections
1. Offset2. Midpoint3. Stretch4. X-Menu5. Slider
Primary finger cursor position & clickSecondary finger cursor speed or C/D
CHI 2006 12
Dual Finger Offset
Fixed offset WRT finger
Ambidextrous control
CHI 2006 13
Dual Finger Midpoint
Cursor ½ distance between fingers
Variable speed control
Max speed reduction is 2x
Dead spots on screen!
CHI 2006 14
Dual Finger Stretch
Inspired by ZoomPointing (Albinsson & Zhai,‘03)
Primary finger anchor Secondary finger
defines the zooming area scales the area in all
directions away from the anchor
CHI 2006 15
Dual Finger Stretch
Offset is preserved after selection!
CHI 2006 16
Zooming Comparison
Bounding Box Zoom Fingers placed OFF
target Target distance
increases w/ zoom
“Stretch” Zoom Primary finger
placed ON target Same motion = 2x
zoom
CHI 2006 17
Dual Finger X-Menu
Crossing Menu (no buttons/no clicks) 4 speed modes 2 helper modes
Cursor notification widget Eyes-free interaction
Freezing cursor Quick offset setup Eliminate errors in noisy conditions
Helpers: Snap – Remove offset Magnification Lens
CHI 2006 18
Dual Finger X-Menu
CHI 2006 19
Dual Finger X-Menu with Magnification Lens
CHI 2006 20
Dual Finger Slider
NormalSlow 4X
Slow 10XFreeze
Snap
CHI 2006 21
Dual Finger Slider
CHI 2006 22
Multi-Touch Table Prototype
Back projected diffuse screen
IR vision-based tracking
Similar to TouchLight (Wilson, ICMI’04)
CHI 2006 23
User Experiments
Measure the impact of a particular technique on the reduction of error rate while clicking
2 parts: Evaluation of SimPress clicking Comparison of Four Dual Finger Techniques
Task: Reciprocal target selection Varying the square target width Fixed distance (100 pixels)
12 paid participants (9 male,3 female, ages 20–40), frequent computer users, various levels of touchscreen use
CHI 2006 24
Part 1: SimPress Evaluation
Within subjects repeated measures design
5 target widths: 1,2,4,8,16 pxls
Hypothesis: only 16 pxls targets are reliably selectable
Results: 8 pixel targets still have ~10% error rate
0102030405060708090
100
1 2 4 8 16
Target Width (pixel)
Per
cent
of
Tria
ls ±
SE
M
F(4,44)=62.598, p<0.001
CHI 2006 25
Part 2: Comparison of 4 Dual Finger Selection Techniques
Compare: Offset, Stretch, X-Menu, Slider Varying noise conditions
Inserted Gaussian noise: σ=0, 0.5, 2 Within subjects repeated measures design:
3 noise levels x 4 techniques x 4 target widths (1,2,4,8 pxls)
6 repetitions 288 trials per user Hypotheses:
Techniques that control the C/D will reduce the impact of noise
Slider should outperform X-Menu
CHI 2006 26
Part 2: Error Rate Analysis
Interaction of Noise x Technique
0
10
20
30
40
50
60
70
Ofset X-Menu Slider Stretch
Err
orR
ate
(%
) ±
SE
M
low medium high
F(6,66)= 8.025, p<0.001
CHI 2006 27
Part 2: Error Rate Analysis
0
20
40
60
80
100
W-1 W-2 W-4 W-8
Err
or
Rate
(%
) ± S
EM
Offset X-Menu Slider Stretch
Interaction of Width x Technique
F(9,99)=29.473, p<0.001
CHI 2006 28
Part 2: Movement Time Analysis
Analysis on median times
Stretch is ~ 1s faster than Slider/X-Menu (t(11)=5.011, p<0.001)
Slider similar performance to X-Menu
0
1
2
3
4
5
6
7
W-1 W-2 W-4 W-8
Mov
emen
t T
ime
(s)
± S
EM
Offset X-Menu Slider Stretch
Missing
CHI 2006 29
Subjective Evaluation
Post-experiment questionnaire (5 pt Likert scale) Most mental effort: X-Menu (~2.88) Hardest to learn: X-Menu ( ~2.09) Most enjoyable: Stretch (~4.12), Slider (~4.08) No significant differences WRT fatigue
Best Technique for Noise Condition
02
46
810
12
Low Noise Medium Noise High Noise
Offset XMenu Slider Stretch
Overall Preference
012345678
Offset X-Menu Slider Stretch
CHI 2006 30
Conclusions and Future Work
Top performer & most preferred: Stretch Slider/X-Menu
Comparable error rates to Stretch No distortion of user interface Cost: ~1s extra
Freezing the cursor (positive feedback) Like “are you sure?” dialog for clicking…
Possible future SimPress extensions: Detect user position/orientation Stabilization of the cursor
Questions
CHI 2006 32
Multi-Touch Tabletops
MERL DiamondTouch (Dietz & Lehigh, ’01)
SmartSkin (Rekimoto, ’02) PlayAnywhere and TouchLight (Wilson,
’04, ’05)
CHI 2006 33
ANOVA Table
Source df F p
Noise (N) (2,22) 20.24 <0.001
Technique (T) (3,33) 169.14 <0.001
Width (W) (3,33) 150.40 <0.001
N x T (6,66) 8.03 <0.001
T x W (9,99) 29.47 <0.001
N x W
N x T x W
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