CS376 Input Techniques

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Input Techniques
Jeffrey Heer 14 May 2009
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Pointing Device Evaluation

• Experimental task target acquisition
• abstract, elementary

• Real task interacting with GUIs
• pointing is fundamental

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Fitts Law Paul Fitts, 1954
MT a b log2 (D/W 1)
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

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Experimental Data
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Considers Distance and Target Size
MT a b log2 (D/W 1)
Target 1
Target 2
Same ID ? Same Difficulty
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Considers Distance and Target Size
MT a b log2 (D/W 1)
Smaller ID ? Easier
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Considers Distance and Target Size
MT a b log2 (D/W 1)
Target 2
Larger ID ? Harder
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What does Fitts law really model?
Target Width
Velocity
(c)
(a)
(b)
Distance
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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) 1.6
• Eyetracker Ware Mikaelian (1987) 13.7

Reference MacKenzie, I. Fitts Law as a research
and design tool in human computer interaction.
Human Computer Interaction, 1992, vol. 7, pp.
91-139
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Using laws to predict performance

• Which will be faster on average?
• Pie menu (bigger targets less distance)?

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Fitts Law Paul Fitts, 1954
MT a b log2 (D/W 1)
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

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Beyond pointing trajectories
Steering Law Accot Zhai
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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)
• NDH operates at a coarse temporal and spatial
  scale DH operates at a finer scales