This document summarizes the results of a study that tested different touchscreen interaction techniques for people with motor impairments. The study tested target sizes of 7mm, 12mm and 17mm and techniques like tapping, crossing, exiting and gesturing in different screen areas like corners, edges and middle. The best target size was found to be 12mm for most techniques but error rates remained high. Interacting at screen edges had lower error rates than the middle. Gesturing was the best technique for edge targets while tapping was best for middle targets. The best technique, size and area combinations are discussed to inform the design of more accessible touch interfaces. Future work could explore differences between able-bodied users and those with motor impairments.

1. Towards Accessible
Touch Interfaces
Tiago Guerreiro
Hugo Nicolau
Joaquim Jorge
Daniel Gonçalves

2. Mobile evolution …

3. Leading to …
Touch Interfaces

4. pleasant

5. Tactile feedback
loss of tactile
feedback

6. Loss of physical stability

7. hard to select targets

8. it occurs to everyone

9. … and motor
impaired

10. require less strength

11. Adapt to users’ needs

12. Provide the knowledge to
build better touch interfaces

13. We performed …

14. Tested several …
Interaction
Techniques

15. Screen areas …
… corners

16. Screen areas …
… edges

17. … and target sizes
7 mm 12 mm 17 mm

18. Tapping

19. Crossing

20. Exiting

21. Gesturing

22. 15 participants
28-64 years old
C4-C7 lesion level
6 left-handed
never used touchscreens

23. Results

24. Error Rate
X

25. Precision

26. Movement Error

27. Movement Time
t0 tn

28. Tapping

29. Target Size
50%
40%
Error Rate (%)
30%
20%
10%
0%
7mm 12mm 17mm
Target sizes (milimeters)

30. Corners and Edges precision

31. Vertical error rate
7mm 12mm 17mm
45% 28% 27%
39% 28% 24%
43% 19% 12%

32. Distance error rate
17mm
28%
20%
12%
28%
11%
20%
12%
11% 6%

33. Crossing

34. Target Size
50%
40%
Error Rate (%)
30%
20%
10%
0%
7mm 12mm 17mm
Target size (milimeters)

35. Exiting

36. Target Size
80%
70%
60%
Error Rate (%)
50%
40%
30%
20%
10%
0%
7mm 12mm 17mm
Target size (milimeters)

37. Gesturing

38. Edges
60
50
Movement Error (pixels)
40
30
20
10
0
Center Edge
Gesture

39. Movement Error (pixels)
0
50
150
200
250
100
NW
NE
SW
SE
SLeft
Directions
N
WUpper
S
E
W
Gesture Direction
SRight
NRight
EUpper
NLeft
WBottom
EBottom

40. Mixing
All
Techniques

41. All Techniques
80%
70%
60%
Error Rate (%)
50%
40%
30%
20%
10%
0%
7mm 12mm 17mm
Target Size (milimeters)
Exiting Gestures Tapping Crossing

43. Interact with edge support

44. Interact with edge support
22%
36%

46. Acquiring edge targets

47. Acquiring edge targets

48. Edge or Middle

49. Edge or Middle

50. Interacting mid-screen

51. Interacting mid-screen
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
7mm 12mm 17mm
Crossing GesturesM4Way Tapping Middle

52. Interacting mid-screen
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
7mm 12mm 17mm
Crossing GesturesM4Way Tapping Middle

54. 5
4
3
2
1
0
Exiting Tapping Crossing Gesturing

55. Conclusions

56. What is the best size for
each interaction technique?

57. 12 mm

58. However, error rates are still …
High

59. What is the best screen
area for each interaction
technique?

63. Regarding target position …
Support

65. What is the best interaction
technique for motor-
impaired people?

68. What is the best interaction
technique for each screen
area?

75. What is the best technique-
size-area combination?

78. Future Work
Explore target size for the target population
Differences between able-bodied and tetraplegics

79. The End
Tiago Guerreiro
tjvg@vimmi.inesc-id.pt