Human-Computer Interaction User Psychology 1 1 1

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

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

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

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

Information Processing Cycle Times (in milliseconds) Average Range Perceptual system 100 50 - 200 Cognitive system 70 25 - 170 Motor system 70 30 - 100 6 6 6

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

7 Stages of Interaction (Norman, 1986)

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

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

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

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

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

“Pigs is Pigs” 14 14 14

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

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

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

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

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