The document summarizes research on techniques for improving selection of small targets on multi-touch screens. It describes issues with finger occlusion and imprecision. Previous approaches are outlined. The paper then introduces dual-finger techniques like offset, midpoint, stretch and an X-menu for navigating without clicks. Experiments compare these and find stretch performed best with fastest times and fewest errors. Stretch was also most preferred. Future work could include cursor stabilization and feedback.

1. Precise Selection Techniques for Multi-Touch Screens By: IQxplorer

2. Selecting a small target is very HARD! CHI 2006

3. Small target size comparison Average finger ~ 15 mm wide CHI 2006 Target UI element Width (abstract screen) Width 17” screen 1024x768 Width 30” screen 1024x768 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)

4. Touchscreen Issues Finger >>> Target Finger occludes the target Fingers/hands shake and jitter Tracking can be noisy (e.g. video) 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) CHI 2006 Sears, A. and Shneiderman, B. “High Precision Touchscreens: Design Strategies and Comparisons with a Mouse.” (’91)

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 Offset Midpoint Stretch X-Menu Slider Primary finger  cursor position & click Secondary finger  cursor speed or C/D CHI 2006

12. Dual Finger Offset CHI 2006 Fixed offset WRT finger Ambidextrous control

13. Dual Finger Midpoint CHI 2006 Cursor  ½ distance between fingers Variable speed control Max speed reduction is 2x Dead spots on screen!

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 CHI 2006 Offset is preserved after selection!

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 CHI 2006 Normal Slow 4X Slow 10X Freeze Snap

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 CHI 2006 F (4,44) =62.598, p<0.001

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 CHI 2006 F (6,66) = 8.025, p<0.001

27. Part 2: Error Rate Analysis CHI 2006 Interaction of Width x Technique F (9,99) =29.473, p<0.001

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 CHI 2006 Missing

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 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 CHI 2006

31. Questions

32. Multi-Touch Tabletops MERL DiamondTouch (Dietz & Lehigh, ’01) SmartSkin (Rekimoto, ’02) PlayAnywhere and TouchLight (Wilson, ’04, ’05) CHI 2006

33. ANOVA Table CHI 2006 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