Transcript COM 3210: Understanding the human element in HCI

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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9
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1
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3
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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) / (3*20 min)
= (30000 yards) / 60 min
= (15*2000 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
Internal devices
External devices
specific rules,
memorised
calculationstables,
formulae
e.g. calculator,
pen and paper,
notes, manuals,
diaries, slides
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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 “precalculated” 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
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 Many similar external
memory aids in computer
systems and “real life”
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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
Graphical
A
B
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77.2
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
HTR LAX MEX DUS COL CHG
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Example: statistical data
Comparison of Grades
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no of students
 User’s 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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10
8
6
4
2
0
grade
girls
boys
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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/
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