1. Human-Computer Interaction
User Psychology 1 1 1

2. Lecture Overview Contribution to HCI Left brain / right brain
Model human processor
Sensory registers
Short term memory
Long term memory
Implications of the model
Other psychological observations 2 2 2

3. User Psychology and HCI
Helps identify target for design
Helps explain success or failure of designs
Provides little prescriptive guidance for design 3 3 3

4. Left brain Right brain Words Images and Patterns
Analysis Overall situation
Logic Spatial relationships
Sequential Parallel
Simple tasks Complex scenes
Must be taught No teaching required 4 4 4

5. The Model Human Processor
Model suppresses detail
Allows simple predictions
Model human as three interacting subsystems
Perceptual system
Cognitive system
Motor system
(Card, Moran and Newell, 1983)
The Model Human Processor 5 5 5

6. Information Processing Cycle Times (in milliseconds)
Average Range
Perceptual system
Cognitive system
Motor system 6 6 6

7. Human Information Processing
External Environment
Sensory Registers
Perception
Consciousness
Short Term Memory
Cognitive Functions
Motor Response
Long Term Memory 7 7 7

8. 7 Stages of Interaction (Norman, 1986)

9. Sensory Registers Temporary buffers
Information in unprocessed / uncoded state
Persistence 0.2 seconds (visual)
2 seconds (audible) 9 9 9

10. Short Term Memory
Temporary storage buffer (20-30 seconds or more with rehearsal)
Symbolically coded information
Limited capacity - 7 plus or minus 2 chunks (Miller, 1956)
Number of chunks independent of bits/chunk
Used for storage and decision-making
Recency effect 10 10 10

11. Long Term Memory Semantically based Virtually unlimited in size
Ease of access related to:
frequency of access / refresh
time since last access
number and type of associative links
interference from other information activated by same associations 11 11 11

12. STM to LTM Link Indirect (no conscious path)
Asymmetric (fast read, slow write) 12 12 12

13. Implications from the Model
Human processing capacity is very small
Constant danger of overload
Implies designers must :
Use meaningful / familiar chunks wherever possible
Simplify decision-making
Minimise STM storage if problem solving / decision-making also required 13 13 13

14. “Pigs is Pigs” 14 14 14

15. Other Psychological Observations: Closure
Strong desire for users to “close” current task and discard information in STM
Make STM available for new info / processing 15 15 15

16. Other Psychological Observations: User Attitude and Anxiety
Negative attitude results in slower learning
Anxiety (e.g. fear of failure) reduces STM capacity and causes slower learning
Workplace politics
Level of training 16 16 16

17. Other Psychological Observations: Control
Inexperienced users
willing to be led slowly by the computer
Experienced users
wish to take the initiative and operate the system rapidly
As people gain experience, so their desire to control the computer increases 17 17 17

18. Other Psychological Observations: Various
Better at recognition than recall
Major rationale for desktop metaphor
Remember grouped things better
Learn by doing
Rely on previous experiences
Differ in how we learn 18 18 18

19. Lecture Review Contribution to HCI Left brain - right brain
Model human processor
Closure
User attitude and anxiety
Control
Various observations 19 19 19