1

CMT 3210: Understanding the human element in HCI

Week 10: External cognition- Designing external representations

Elke Duncker / Paola Amaldi-Trilló

2

Topics

Cognition as involving external and internal structures and processes

External representations that support cognitionWhen and how to design external

representations

3

The story so far….

Design of information 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 formats for representing information?

Relationship between type of task and type of information displayed?

4

Example: a game

Two playersnumbers 1, 2, 3, 4, 5, 6, 7, 8, 9Each 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.

5

How to turn it into an easier taks:

2 7 6

9 5 1

4 3 8

6

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”

7

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 : 2000 yards) / (3:60 min)= (1500/2000) * (60/3)= 15 knots

8

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.

9

Using a three scale nomogram

Specialised external artefactOptimises distance / speed / time calculationsSimplifies the organisation of the task

10

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

11

Theory

How do these devices work?Need to look beyond human information

processing psychology which focuses on characteristics of individual cognition cognitive system of person plus external

representations External representations are converted by some

cognitive mechanisms into internal representation

12

Theory (2)

External Cognition look outside the head of the individual. The unit of

analysis is the human-machine system

cognitive process involve the co-ordination of internal and external structures among individuals. What does individual cognition become when it is

shared between individuals?

13

External distributed cognition

Individuals performing a task

External resources

e.g. calculator, peers, team

notes, manuals,diaries.

Internal devices

specific rules,memorized calculation

stables,formulae

Distributed Cognition

14

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

15

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?

16

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

17

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?

18

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

19

Perceptual inferences

The history of use is available in many ways. It informs our interactions with artifacts. For ex., well-used pad on the door new paperback most recently used papers seating on top of the pile

20

Example

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

easiest?

22.7 77.2

A B A B

Graphical Digital

21

Example: airline information

HTR

MEX

DUS

COL

CHG

LAX

MEX DUS COL CHGLAXHTR

Users task: find cheapest flight

Cost represented by size Cost judgements

achieved by perceptual operation

22

Example: statistical data

User’s task: compare female student results to male student results. Who is more successful?

Numbers and results represented graphically

Comparison achieved perceptually

Comparison of Grades

0

2

4

6

8

10

12

14

16

grade

no o

f stu

dent

s

girls boys

23

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

24

Further reading

Scaife, M. & Rogers, Y. (1996) External Cognition: How Do Graphical Representations Work? Int. Journal. 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).

25

Further readings

Hollan, J., Hutchins, E., & Kirsh, D. (2001). Distributed cognition: Towards a new foundation for human-computer interaction research. In J.M. Carroll (ed.) (2001) Human-computer interaction in the new millenium. Addison-Wesley.

Hutchins, E. (1996) Cognition in the Wild. MIT Press.

Jiajie Zhang's papers: http://acad88.sahs.uth.tmc.edu/