1. Input: Devices and Theory

2. Input for Selection and
Positioning
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Devices
Power Law of Practice
Fitt’s Law (2D, 3D lag)
Eye hand coordination
Two handed
Methods and Metaphors

3. 5 Virtual DevicesAdapted from Wallace, 1976.
"The Semantics of Graphic Input Devices"
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Button - Indicates Choice (binary)
- radio buttons are an extension of this concept.
Keyboard - Alpha numeric strings
- a lot of buttons (voice)
Pick Device - For selection of graphic objects
The canonical example of this is a light pen.
Locator - For specifying screen coords
- x, y position(e.g. mouse)
Valuator - generating floating point values:
A potentiometer.

6. Power Law of Practice

Time to perform a task is proportional to the log
of the number of times the task has been carried
out.
log(Tn) = log(T1) - α.log(n)

The law is usually expressed in terms of blocks
of trials since the time to perform a single trial is
too variable.

7. Law of
Diminishing
Returns
Applicable to
Choice reaction
Typing
Many skilled behaviors

8. Fitt’s Law for position selection

MeanTime = C1 + C2log2(D/W + 0.5) (1)
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MeanTime = C1 + C2log2(D/W + 1.0) (2)
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Index of difficulty = log2(D/W + 1.0)
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Index of performance = 1/C2
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About 5-8 bits per second (many devices)

9. Modified Fitt’s Law
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MeanTime = C1 + C2(Human + Machine)ID

10. Control loop
Detect start
signal
No
Human Processing
Judge distance
to target
Effect hand
movement
In
Target?
Yes
Machine Processing
Update display
On to next task
Measure
hand position

11. Fish Tank VR (is head pos
important) is stereo important.
Head Position Tracking
Stereo Glasses
Ar
Mirror
Phantom
Virtual Image of Screen
Arsenault and Ware (2001) TOCHI

12. Effects of incorrect perspective

14. Task: Tapping from target to
target

15. Effects of stereo in eye hand
coordination
Approx 3 bits per second (best case)
Mean Time (sec)
4
3
No Stereo
2
Stereo
1
0
0
1
2
3
4
Index of Difficulty (bits)
5
6

16. Effects of correct perspective
(HT)
Mean Time (sec)
4
3
No HT
2
HT
1
0
0
Index of
Performance
Summary
1
2
3
4
5
6
Index of Difficulty (bits)
No Stereo
Stereo
No HT
1.58
2.41
HT
1.75
2.70
In bits per second

17. Factors in input device design
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Degrees of Freedom
Order of control (Milgram) p = a + bt + ct2
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Mappings between devices and tasks
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Position (0)
Velocity (1)
Acceleration (2)
S-R compatibility
Integral/separable
Isometric/compliant

18. Direct Manipulation
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Visibility of objects and actions
Rapid reversability
< 100 msec lag in visual feedback
Users
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Feelings of mastery and control
Ease of learning
Perceived Transparency “The user is able to apply
intellect directly to the task; the tool itself seems to
disappear”. (Rutowsky, 1982)

19. 3D Rotations with a 2D interface
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Virtual Trackball (Chen, 17.5 seconds,
Hickley 26 sec.)
Arcball 26 seconds (Hinckely, 1997
Shoemake 1992)

20. Rotations 3dof
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Ware: 55 seconds accuracy, 14 seconds
speed
Hinckley 3ball 20.7 f sec 14 m sec
Zhai 18 sec.
Wang: real object rotations of 45 deg in
less than a second
Ware and Rose: real object rotation <
2sec virtual objects, real handles

21. Handles Real and Virtual
Ware and Rose

22. Real Object Rotations
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Hand in the same place as an object helps

23. Where, between real and virtual
does performance break down?
Monitor
Mirror

24. Ware and Rose: results
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Hand in the same place as an object helps
(30 %).
Random end harder than random start.
Sphere vs shape match is a minor factor

25. Experiment
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Two objects:
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Wire-frame, color coded tetrahedron
Solid shape

26. Results
Color result confirms
Hypothesis
Ineficiency (percent)
600
500
400
solid
300
wire
200
100
0
ball
No major difference
In efficiency
rod
vSphere
10
9
Time (seconds)
8
7
6
solid
5
wire
4
3
2
1
0
ball
rod
vSphere

27. Radical solutions
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Gadget methods
Screen space methods

28. Props: Physical Objects that
Support Interaction (Hinckley)

29. Guiard’s Kinematic Chain Theory
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The left and right hands make up a functional
kinematic chain: for right-handers, the right hand
moves relative to the output of the left hand.
General principles:
1. Right-to-left reference: The right hand
performs its motion relative to the frame of
reference set by the left hand.
2. Asymmetric scales: Different temporal-spatial
scales of motion.
3. Left hand precedence: The left hand precedes
the right: for example, the left hand first positions
the paper, then the right hand begins to write.

30. Two Handed Interaction
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Props
Toolglasses and magic lenses
Tool use, e.g. rulers and guides

31. Gestures

32. 
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Gestures can speed up input
Can be iconic
Sketch beautification
Erase, create objects, etc.

33. Dynamic Querie (Schneiderman)
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Interactively expose an hide multidimensional discrete data.
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One slider per data dimension.

34. Frames of Reference
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Retinocentric (2df) look at something
Head centered (2df) pan and tilt
Torso centered (2df) turn move forward
Hand centered (6df) object orientation
Exocentric: Object centered point
direction, intersection, docking, ROV
control