More Laws of HCI EEE459'14

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More Laws of HCIEEE459.14
Royal Military College of Canada Electrical and
Computer Engineering

• Professor Greg Phillips
• Greg.Phillips_at_rmc.ca
• 1-613-541-6000 ext. 6491

Major JW Paul Jeff.Paul_at_rmc.ca 1-613-541-6000
ext. 6656
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References

• MacKenzie, I. Fitts Law as a research and design
  tool in human computer interaction. Human
  Computer Interaction, 1992, Vol. 7, pp. 91-139
• Beyond Fitts Law Models for trajectory based
  HCI tasks. Proceedings of ACM CHI 1997
  Conference
• Other HCI Courses
• http//www.cs.ubc.ca/cs444/
• http//www-faculty.cs.uiuc.edu/bpbailey/teaching/
  2004-Fall/cs498/
• http//hci.ethz.ch/seminar/

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Laws

• Fitts Law
• Steering Law
• Webers Law
• Hicks Law
• Power Law of Practice

log 2 ( x ) log10( x ) / log10 ( 2 )
log10( x ) / 0.301
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Fitts Law
target zone
W
amplitude of deflection to target
A
starting point

• MT a b log2 (A/W 1)
• where
• a reaction time, time to click (constants of
  the task and device)
• b speed of device in sec/bit

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Fitts constants
1/b IP (information processing speed of
device)
Reference MacKenzie, I. Fitts Law as a research
and design tool in human computer interaction.
Human Computer Interaction, 1992, Vol. 7, pp.
91-139
Other studies have also looked at elbow vs wrist
vs arm, etc effects
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Fitts Example Problem
MT a b log2 (A/W 1) a 630, b 200

• Let us assume a particular button/situation has a
  
• MT 1630msec
• What happens if we make the target four times
  larger?

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Fitts Solution
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Steering Law

• many tasks require navigating a menu structure
• equivalent to following a tunnel
• Fitts law not sufficient to model this

Beyond Fitts Law Models for trajectory based
HCI tasks.Proceedings of ACM CHI 1997 Conference
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Steering task
W(s)

• MT a b

ds
? ?
W(s)
ID index of difficulty Recall for Fitts law
this was log2 (A/W 1) (can also have simpler
shapes - and thus simpler ID)
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• 1 goal to pass through

• 2 goals to pass through

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Hicks Law

• decision time is based on number of choices
• T a b log2(n1)
• where
• n number of choices
• a, b empirically determined constants
• T time to make decision
• does not include acting on decision

Fitts Law, but in this case log2(n1)
represents amount of information processed by
human operator (in bits)
note this is slightly more complex if the
probability of selecting each option is not equal
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Hicks Law Example
T a b log2(n1) a 10, b 20

• Compare 1 menu of 16 items
• Vice 2 menus of 8 items

Recall, this does not include acting on the
decision
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Using Hicks Law
Common actions at the top (thus not all are
searched)
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Power Law of Practice

• task time on nth trial follows a power law
• Tn T1 n-a, where a .4 (empirically
  determined)
• i.e., you get faster the more times you do it!
• applies to skilled behavior (sensory motor)
• does not apply to knowledge acquisition or
  quality
• note studies have shown that directional motor
  memory is more effective than distance
• thus pie menus with direction can be
  recalled more efficiently by experienced users

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Back to our disappearing menu
You can never practice the same choice thus
Hicks Law always applies no practice allowed!
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Webers Law

• The smallest perceptible difference between two
  things is a constant 0.16
• applies to size, luminosity, etc
• also applies to number of items
• up to 5 items, k is greater than .16 so you can
  easily count them
• beyond that, lots

?S/S k
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How Many Items?
Now, watch carefully, is there the same, more or
less on the next slide?
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How Many Items?
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Excellent, lets try again
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Excellent, lets try again
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What happened?

• In the first example we had three items, and
  added one
• In the second example we had twelve items and
  dropped one

?S/S 1/3 .333 gt .16
?S/S 1/12 .083 lt .16
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Another Webers Law example
Is the quarter the right size?

• Dime 18mm
• Nickel 21mm
• Quarter 23.5mm

What size should it be?
Thus it should be 24.36mm (about one mm bigger!)
.16 x/21 3.36
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Questions?