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User Psychology

Human-Computer Interaction

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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

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User Psychology and HCI

Helps identify target for design Helps explain success or failure of designs Provides little prescriptive guidance for

design

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Left brain Right brainLeft brain Right brain

Words Images and PatternsWords Images and Patterns

Analysis Overall situationAnalysis Overall situation

Logic Spatial relationshipsLogic Spatial relationships

Sequential ParallelSequential Parallel

Simple tasks Complex scenesSimple tasks Complex scenes

Must be taught No teaching requiredMust be taught No teaching required

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T

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

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Information Processing CycleTimes (in milliseconds)

Perceptual system 100 50 - 200

Cognitive system 70 25 - 170

Motor system 70 30 - 100

Average Range

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Human Information Processing

External Environment

Sensory Registers

Perception

Consciousness

Short Term Memory

Cognitive Functions

Motor Response

Long Term Memory

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7 Stages of Interaction (Norman, 1986)

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Sensory Registers

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

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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

Short Term Memory

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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

Long Term Memory

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STM to LTM Link

Indirect (no conscious path) Asymmetric (fast read, slow write)

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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

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“Pigs is Pigs”

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Other Psychological Observations: Closure

Strong desire for users to “close” current task and discard information in STM

Make STM available for new info / processing

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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

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Other Psychological Observations: Control

As people gain experience, so their desire to control the computer increases

Inexperienced users– willing to be led slowly by the computer

Experienced users– wish to take the initiative and operate the system

rapidly

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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

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Lecture Review

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