CMT 3210: Understanding the human element in HCI

1. CMT 3210: Understanding the human element in HCI Week 10: External cognition - Designing external representations Elke Duncker

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

3. 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?

4. 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.

5. How to turn it into an easier taks:

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 * 20 yards) / (3*20 min)= (30000 yards) / 60 min= (15*2000 yards) / 1h= 15 nm/h= 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 artefact • Optimises distance / speed / time calculations • Simplifies the organisation of the task

10. 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 The Three Minute Rule Answer = 15 knots

11. 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

12. 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

13. 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

14. 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?

15. “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” Example 237.4

16. 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?

17. 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

18. 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

19. Users task: find cheapest flight Cost represented by size Cost judgements achieved by perceptual operation Example: airline information HTR LAX MEX DUS COL CHG HTR LAX MEX DUS COL CHG

20. User’s task: compare female student results to male student results. Who is more successful? Numbers and results represented graphically Comparison achieved perceptually Example: statistical data

21. 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

22. 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/