The document summarizes a research paper that studied how activating buttons at the point of impact can improve rapid button pressing. The researchers found that activating buttons at the point of maximum force (impact activation), compared to traditional activation, led to better temporal accuracy as measured by higher success rates and lower variability in asynchrony between button presses and stimuli. Impact activation took advantage of the stronger tactile sensation at the point of impact to help users better calibrate their responses. The findings suggest activation point setting is an important design parameter and analog sensing technologies may have advantages for tasks requiring precise timing of inputs.

1. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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• Impact Activation Improves Rapid Key Pressing Mon 16.30-17.50 516E
• Neuromechanics of Button Press Tue 11:00-12:20 518AB
• Moving Target Selection: A Cue Integration Model Tue 11:00-12:20 518AB

2. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Watch carefully...
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3. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Watch carefully...
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4. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Watch carefully...
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5. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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6. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
A button press.
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7. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
10x slower
one button press
= approx. 100 ms
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8. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018

9. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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Target
The ultimate button press: Input registration
at the precise moment aligned with the intended timing.
Intended Point
Button press

10. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Keystroke itself
is continuous.
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but registration is on point in time.

11. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
• Activation point is the point of signal registration during button press.
• Activation point setting has became a design parameter.
Activation point
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Logitech Romer-G switch
https://www.logitechg.com/en-us/
articles/romer-g
Aimpad
http://aimpad.com/aimpad-vs-
flaretech/
Flaretech
https://wooting.helpscoutdocs.com/
article/28-flaretech-switch-mechanics

12. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018

13. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Switch mechanism
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source: http://www.keyboardco.com/blog/index.php/2012/12/an-introduction-to-cherry-mx-mechanical-switches/
https://sitesdoneright.com/blog/2013/02/why-my-mechanical-computer-keyboard-is-better-than-your-keyboard

14. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
1.0
10 ms
2.0
3.0
4.0
(mm)
0.5
0
Displacement
Time(A)
Traditional Activation
(B)Fingertipforce
1.0
1.5
2.0 (N)
Impact Activation
compression release
Time
impact
Impact Activation
Activating a button at its impact point
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15. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018

16. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Listen and tap
to the rhythm
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17. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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Displacement
* 100 keystrokes

18. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
AveragedDisplacement
Traditional Activation
Impact Activation
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-50 ms
-15 ms

19. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Rationale and hypothesis
• At the impact point, maximum energy is transferred to the mechanoreceptors of the
fingertip [14].
• When perceived timing matches with the stronger sensation, users should be better
able to calibrate their responses with the displayed stimulus [16]
• Hypothesis
• Better calibration of button pressing with IA
• The effect is more pronounced in fast tapping task. (less temporal noise [34])
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1.0
10 ms
2.0
3.0
4.0
(mm)
0.5
0
Displacement
Time(A)
Traditional Activation
(B)
Fingertipforce
1.0
1.5
2.0 (N)
Impact Activation
compression release
Time
impact
≈ strength of mechanoreceptor stimulation

20. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
The change seems subtle.
Is there any difference?
1.0
10 ms
2.0
3.0
4.0
(mm)
0.5
0
Displacement
Time(A)
Traditional Activation
(B)
Fingertipforce
1.0
1.5
2.0 (N)
Impact Activation
compression release
Time
impact
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10-20 ms

21. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Even 10 ms matters.
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22. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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* 10x slower
Target Zone (50 ms)
Key activation
Traditional Activation

23. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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* 10x slower
Target Zone (50 ms)
Key activation
Impact Activation

24. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Implementation
• "Analog" sensing is required
• Optical, force, capacitance, magnetic, etc.
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25. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Algorithm
• Algorithm: detecting the first local maxima in button press
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1.0
10 ms
2.0
3.0
4.0
(mm)
0.5
0
Displacement
Time
Fingertipforce
1.0
1.5
2.0 (N)
compression release
Time
impact

26. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Implementation - Physical
• Displacement sensing by magnet and hall-effect sensor.
• Scan rate: 542 Hz
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Magnet
Hall-effect sensor
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
-40 -20 0 20 40 60 80 100
50 ms

27. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Implementation - Touch
• Touch area sensing by capacitance change
• Scan rate: 542 Hz
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0
10
20
30
40
50
60
70
80
-40 -20 0 20 40 60 80 100 120
50 ms
Touch sensor
module
(MPR121)

28. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Experiment
• Goal: to assess the effect of Impact Activation in terms of temporal accuracy
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Target
Activation

29. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Task
• "Please try to activate the button WITHIN the target"
• "Maximize the number of successful trial"
• "Adjust your button press timing"
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Failure Success Failure
...Sound
Button press
Interval Target Width
Repeat x100
Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018

30. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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In this experiment, we measured...
• Success Rate
= # success trials / # total trials
• Mean Asynchrony
= mean of asynchronies
(=time difference between input and the stimuli signal onset)
• Standard Deviation of Asynchrony
Mean Asynchrony
Data Analysis

31. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Experiment design
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32. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Results: success rate
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24.6% 27.0%
48.0%
37.1%
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
Physical Touch
Task Succss Rate
Traditional
Impact
94.9% increase
(23.4%p)
37.4% increase
(10.1%p)

33. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Result: Asynchrony
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Physical
Impact Activation Traditional Ac
+50
+100
+50
0
-50
-100
-150
+100
ms)Asynchrony(ms)
Target width = 50 ms 100 ms
Mean
Asynchrony
+-1 σ line
+-2 σ line
Interval Target Width

34. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Result: Asynchrony
!34
Physical
Impact Activation Traditional Ac
+50
0
-50
-100
-150
+100
ms)Asynchrony(ms)
Interval
200ms
300ms
400ms
500ms
600ms
Interval Target Width

35. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Result: Asynchrony
!35
Physical
Impact Activation Traditional Ac
+50
0
-50
-100
-150
+100
ms)Asynchrony(ms)
Interval Target Width
Slope
: Robustness against interval changes
Accuracy
: near-zero is better

36. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Result: Asynchrony
!36
Physical
Impact Activation Traditional Ac
+50
+100
+50
0
-50
-100
-150
+100
ms)Asynchrony(ms)
Interval Target Width
Variance (=precision)
: narrower one indicates better precision
±1σ ≈ 68%
±2σ ≈ 95%

37. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Result: Asynchrony
!37
Physical
Impact Activation Traditional Activation
Touch
Tone interval (from 200-600 ms)
Tone duration Mean asynchrony ±1σ ±2σ
+50
0
-50
-100
-150
+100
+50
0
-50
-100
-150
+100
Asynchrony(ms)Asynchrony(ms)
Physical
Impact Activation Traditional Activation
+50
0
-50
-100
-150
+100
Asynchrony(ms)Asynchrony(ms)

38. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Result: Asynchrony
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Physical
Impact Activation Traditional Activation
Touch
+50
0
-50
-100
-150
+100
+50
0
-50
-100
-150
+100
Asynchrony(ms)Asynchrony(ms)
• Accuracy
• Physical > Touch
• Impact > Traditional
• Slope
• Physical-Impact was the best
• Impact < Traditional

39. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Result: Asynchrony
!39
Physical
Impact Activation Traditional Activation
Touch
Tone interval (from 200-600 ms)
Tone duration Mean asynchrony ±1σ ±2σ
+50
0
-50
-100
-150
+100
+50
0
-50
-100
-150
+100
Asynchrony(ms)Asynchrony(ms)
• Variance
• Impact < Traditional
Tone interval (ms)
200 300 400 500 600 200 300 400 500 600
St.Dev.ofAsynchrony
80
(ms)
60
40
20
Tone duration = 50 ms Tone duration = 100 ms
Overall
Average
47.3
48.7
51.6
52.2
Physical
Impact
Physical
Traditional
Touch
Impact
Touch
Traditional

40. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Implications
• Analog keyswitch technology has advantages.
• Deeper activation point is better for timing precision.
• Activation point setting becomes a design parameter.
!40
Logitech Romer-G switch
https://www.logitechg.com/en-us/
articles/romer-g
Aimpad
http://aimpad.com/aimpad-vs-
flaretech/
Flaretech
https://wooting.helpscoutdocs.com/
article/28-flaretech-switch-mechanics

41. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
Future challenges
• Limited to a specific modality combination: audio stimulus / visual feedback.
• Long-term adaptation has not been tested.
• Tested only two specific buttons (4 mm tactile button and zero-travel touch button)
and sensors (displacement and touch area).
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42. Sunjun Kim, Byungjoo Lee, Antti Oulasvirta, Impact Activation Improves Rapid Button Pressing, CHI 2018
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Questions?
Summary
• Set the right activation point is crucial.
• Impact Activation is a new principle of
activation regarding human tactile
perception.
• Impact Activation improves both temporal
accuracy (2x success rate) and precision.
Physical
Impact Activation Traditional Activation
Touch
+50
0
-50
+100
+50
0
-50
-100
-150
+100
ynchrony(ms)Asynchrony(ms)
• Impact Activation Improves Rapid Key Pressing Mon 16.30-17.50 516E
• Neuromechanics of Button Press Tue 11:00-12:20 518AB
• Moving Target Selection: A Cue Integration Model Tue 11:00-12:20 518AB
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