CMT 3210: Understanding the human element in HCI

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CMT 3210 Understanding the human element in HCI

• Week 10 External cognition
• - Designing external representations
• Elke Duncker

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Topics

• Cognition as involving external and internal
  structures and processes
• External representations that support cognition
• When and how to design external representations

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The story so far.

• Design of displays
• on the basis of characteristics of human
  perception
• Feedback to support the development of mental
  models
• for interpretation, evaluation, decision making
  and learning
• How can we make tasks easier by using certain
  types of displays?
• Relationship between type of task and type of
  display?

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Example a game

• Two players
• numbers 1, 2, 3, 4, 5, 6, 7, 8, 9
• Each player takes a number each turn. This number
  is no longer available.
• The game continues until all numbers have been
  taken or until one of the players has three
  numbers that add up to 15.
• The first player with three numbers that add up
  to 15 wins.

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How to turn it into an easier taks
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Example Calculation

• Calculations in navigation
• A ship travels 1500 yards in 3 minutes.
• What is its speed in knots?
• How is this done?
• use
• Pen, paper,
• Calculator, 1 nm 2000 yards, 1h 60 min, D
  ST
• Three scale nomogram
• Three minute rule

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Using pen and paper

• Required knowledge
• 1 nm 2000 yards, 1h 60 min,
• 1 knot nm/h, Speed Distance/Time
• speed (1500 yards) / (3 min) (1500 20
  yards) / (320 min) (30000 yards) / 60 min
  (152000 yards) / 1h 15 nm/h 15 knots

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Using a calculator

• Required knowledge
• 1 nm 2000 yards, 1h 60 min,
• 1 knot nm/h, Speed Distance/Time
• Calculator steps
• 60 / 3 20
• result 1500 30000
• result / 2000 15
• answer 15knots
• seems easier, but you have to know what you are
  doing before you start.

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Using a three scale nomogram

• Specialised external artefact
• Optimises distance / speed / time calculations
• Simplifies the organisation of the task

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The Three Minute Rule

• Specialised internal artefact
• Tailored for use in navigation
• Time interval, units and task fit together
• 1500 yards in 3 minutes.
• Speed in knots?

• Number of hundreds of yards travelled in three
  minutes
• speed in knots

Answer 15 knots
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Theory

• How do these devices work?
• Need to look beyond information processing
  psychology
• External Cognition
• look outside the head of the individual
• cognitive system of person plus external
  representations
• cognitive process involve the co-ordination of
  internal and external structures

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External cognition
Individual performing a task
Cognition
External devices e.g. calculator, pen and
paper,notes, manuals,diaries, slides
Internal devices specific rules,memorised
calculationstables,formulae
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Mechanisms of external cognition

• External memory
• memory the composition of internal memories and
  external representations
• Computational offloading
• computations and cognitive tasks can be
  pre-calculated and embedded in external
  representations
• Transformation from cognitive into perceptual
  tasks
• form of external representation can transform
  hard mental operations into easier perceptual
  ones

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External memory

• External artefacts often used to enhance internal
  human memory
• Often created specially for the purpose of
  remembering
• Memory function relies on the combination of
  internal and external components
• Examples?

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Example

• Speed bugs
• markers set by pilot to indicate desired speed
• Serve as a memory
• reducing the burden on internal memory
• Many similar external memory aids in computer
  systems and real life

237.4
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Computational offloading

• Reduce cognitive effort by choosing
  representations that transform tasks into
  simpler, but equivalent ones
• Example Multiply 1011(2) by 10(2)
• either 11(10) x 2(10) (external representation
  changes)
• or shift to left by one digit 1011 x 10 10110
  (internal specific rule applied)
• More examples?

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From cognitive to perceptual tasks

• Perceptual inferences can allow users to easily
  gain information about
• distance and proximity
• size
• spatial coincidence
• colour
• etc.
• Perceptual operations often easier and quicker
  than other cognitive operations

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Example

• Which display shows the larger value?
• Which type of display makes the comparison
  easiest?

A
B
A
B
22.7
77.2
Graphical
Textual
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Example airline information

• Users task find cheapest flight
• Cost represented by size
• Cost judgements achieved by perceptual operation

HTR
LAX
MEX
DUS
COL
CHG
MEX
DUS
COL
CHG
LAX
HTR
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Example statistical data

• Users task compare female student results to
  male student results. Who is more successful?
• Numbers and results represented graphically
• Comparison achieved perceptually

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Summary Designing external representations

• Support external memories
• offer external memory functions
• allow users to create them
• Find ways of pre-computing
• make relationships explicit in representations
• Choose representations that simplify cognitive
  work
• Choose representations that support perceptual
  operations rather than cognitive ones

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Further reading

• Scaife, M. Rogers, Y. (1996) External
  Cognition How Do Graphical Representations Work?
  Int. Jnl. of Human-Computer Studies, 45, 185-213
• Casner, S. (1991) A Task Analytic Approach to the
  Automated Design of Graphic Presentations. ACM
  Trans. on Graphics. 10(2).
• Hutchins, E. (1996) Cognition in the Wild. MIT
  Press.
• Jiajie Zhang's papers http//acad88.sahs.uth.tmc.
  edu/