Transcript CS376 Input Techniques

stanford hci group
/ cs376
Input Techniques
Jeffrey Heer · 14 May 2009
http://cs376.stanford.ed
Pointing Device
Evaluation
Real task: interacting with GUIs
 pointing is fundamental
Experimental task: target acquisition
 abstract, elementary
W
D
2
Fitts’ Law [Paul Fitts, 1954]
MT = a + b log2 (D/W + 1)
Index of Difficulty (ID )
a, b = constants (empirically derived)
D = distance
W = size
Index of Performance (IP ) = 1/b (bits/s)
Models well-rehearsed selection task
MT increases as the distance to the target
increases
MT decreases as the size of the target increases
4
Experimental Data
Considers Distance and Target Size
MT = a + b log2 (D/W + 1)
Target 1
Same ID → Same
Difficulty
Target 2
Considers Distance and Target Size
MT = a + b log2 (D/W + 1)
Target
1
Target 2
Smaller ID → Easier
Considers Distance and Target Size
MT = a + b log2 (D/W + 1)
Target
1
Target 2
Larger ID → Harder
What does Fitts’ law
really model?
Target Width
Veloci
ty
(c)
(a)
(b)
Distance
9
Comparing device performance
Device
Study
IP
(bits/s)
Hand
Fitts (1954)
10.6
Mouse
Card, English, & Burr (1978)
10.4
Joystick
Card, English, & Burr (1978)
5.0
Trackball Epps (1986)
2.9
Touchpad Epps (1986)
Reference:
1.6
MacKenzie, I. Fitts’ Law as a research and design tool in human computer
interaction. Human
Computer
Interaction, (1987)
1992, vol. 7, pp. 91-139
Eyetracker
Ware
& Mikaelian
13.7
10
Using laws to predict
performance
Which will be faster on average?
 Pie menu (bigger targets & less distance)?
Pop-up Linear Menu
Pop-up Pie Menu
Today
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
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Fitts’ Law [Paul Fitts, 1954]
MT = a + b log2 (D/W + 1)
Index of Difficulty (ID )
a, b = constants (empirically derived)
D = distance
W = size
Index of Performance (IP ) = 1/b (bits/s)
Models well-rehearsed selection task
MT increases as the distance to the target
increases
MT decreases as the size of the target increases
Beyond pointing: trajectories
Steering Law
Accot & Zhai
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15
EdgeWrite
Corner-based text input
Uses physical constraints
 Hard edges and corners
 Can help offset motor
impairments
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Crossing UIs
[Apitz & Guimbretière
04]
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Yves Guiard: Kinematic
Chain
Asymmetry in bimanual activities
“Under standard conditions, the
spontaneous writing speed of
adults is reduced by some 20%
when instructions prevent the
non-preferred hand from
manipulating the page”
Non-dominant hand (NDH) provides
a frame of reference for the
dominant hand (DH)
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