User Interface Design

1. Jan 20, 2011 IAT 334 1
IAT 334
Interface Design
Cognitive Aspects (Review)
Usability Principles
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Agenda
 Cognitive Processes
– Implications
– Motor system
 Usability Principles
– Learnability Principles
– Flexibility Principles
– Robustness Principles

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Basic HCI
 Model Human Processor
– A simple model of human cognition
– Card, Moran, Newell 1983
 Components:
– Senses
– Sensory store
– Short-term memory
– Long-term memory
– Cognition

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Model Human Processor
Basics
 Based on Empirical Data
 Three interacting subsystems
– Perceptual (read-scan)
– Cognitive (think)
– Motor (respond)

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Information Processing
 Usually serial action
– Respond to buzzer by pressing button
 Usually parallel recognition
• Driving, reading signs, listening to radio

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Processes
 Four main processes of cognitive system:
– Selective Attention
– Learning
– Problem Solving
– Language

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Selective Attention
 We can focus on one particular thing
– Eg cocktail party talk
 Salient visual cues can facilitate s.a.
– Examples?
– Bold, Larger fonts

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Learning
 Procedural Learning:
– How to do something
 Declarative Learning:
– Facts about something
 Involves
– Memorization
– Understanding concepts & rules
– Acquiring motor skills
– Automization

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Learning
 Facilitated
– By analogy
– By structure & organization
– If presented in incremental units
– Repetition
 Use user’s previous knowledge in interface
– Hence, I hate PowerPoint 07!

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Observations
 Users focus on getting job done, not
learning to effectively use system
 Users apply analogy even when it doesn’t
apply
– Mac Trashcan for disk eject

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Problem Solving
 Storage in LTM, then application
 Reasoning
– Deductive- If P then Q, P
– Inductive- If P then Q, Q
– Abductive- Generalization

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Observations
 People are more heuristic than algorithmic
 People often choose suboptimal strategies
for low priority problems
 People learn better strategies with
practice

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Implications
 Allow flexible shortcuts
– Forcing lengthy, mechanistic plans on user
will bore them
– Quick Keys! ALT-Q to Quit
 Have active rather than passive help
– Recognize waste

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Language
 Rule-based
– How do you make plurals?
 Productive
– We make up sentences
 Key-word and positional
– Patterns
 Should systems have natural language
interfaces?

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People
 “Good”
– Infinite capacity LTM
– LTM duration &
complexity
– High-learning
capability
– Powerful attention
mechanism
– Powerful pattern
recognition
 “Bad”
– Limited capacity STM
– Limited duration STM
– Unreliable access to
LTM
– Error-prone processing
– Slow processing

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Recap
 I. Senses
– A. Sight
– B. Sound
– C. Touch
 II. Information processing
– A. Perceptual
– B. Cognitive
• 1. Memory
– a. Short term
– b. Medium term
– c. Long term
• 2. Processes
– a. Selective attention
– b. Learning
– c. Problem solving
– d. Language
– C. Motor system

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UI Design Principles
 Categories
– Learnability
• support for learning for users of all levels
– Flexibility
• support for multiple ways of doing tasks
– Robustness
• support for recovery
 Always think about exceptions, suitability

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Learnability Principles
 Predictability
 Synthesizability
 Familiarity
 Generalizability
 Consistency

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Predictability
 I think that this action will do…
 Operation visibility - can see avail actions
– e.g. menus vs. command shell
– grayed menu items

20. Predictable?
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Synthesizability
 From the resulting system state, My
previous action did…
– compare in command prompt vs UI
– same feedback needed for all users, all apps?

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Familiarity
 Does UI task relate real-world task or
domain knowledge?
– to anything user is familiar with?
– Use of metaphors
• pitfalls
– Are there limitations on familiarity?

23. Familiarity
 What does the blinking green traffic light
mean in Ontario?
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Generalizability
 Does knowledge of one UI apply to
others?
– Cut and paste in many apps
 Does knowledge of one aspect of a UI
apply to rest of the UI?
– File browsers in MacOS/ Windows
 Aid: UI Developers guidelines

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Consistency
 Similar ways of doing tasks
– interacting
– output
– screen layout
 Is this always desirable for all systems, all
users?

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Flexibility Principles
 Dialog Initiative
 Multithreading
 Task migratibility
 Substitutivity
 Customizability

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Dialog Initiative
 System pre-emptive
– system does all prompts, user responds
• sometimes necessary
• Eg. Bank machine
 User pre-emptive
– user initiates actions
• more flexible

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Multithreading
 Two types
– Concurrent
• input to multiple tasks simultaneously
– Interleaved
• many tasks, but input to one task at a time

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Task migratability
 Ability to move performance of task to
entity (machine or person) that can do it
better
– Eg. Autopilot
– Spellchecking
– When is this good? Bad?

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Substitutivity
 Flexibility in details of operations
– Allow user to choose suitable interaction
methods
– Allow different ways to
• perform actions
• specify data
• configure
– Allow different ways of presenting output
• to suit task, user

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Customizability
 Ability to modify interface
– By user - adaptability
– By system - adaptivity

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Robustness Principles
 Observability
 Recoverability
 Responsiveness
 Task Conformance

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Observability
 Can user determine internal state of
system from observable state?
– Browsability
• explore current state (without changing it)
– Reachability
• navigate through observable states
– Persistence
• how long does observable state persist?

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Recoverability
 Ability to continue to a goal after
recognizing error
• Difficulty of Recovery procedure should relate to
difficulty of original task
– Forward Recoverability
• ability to fix when we can’t undo?
– Backward Recoverability
• undo previous error(s)

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Responsiveness
 Rate of communication between user and
system
– Response time
• time for system to respond in some way to user
action(s)
– Stability principle
• response time, rate should be consistent
– As computers have gotten better, required
computer response has gotten shorter

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Task Conformance
 Task coverage
– can system do all tasks of interest?
 Task adequacy
– Can user do tasks?
– Does system match real-world tasks?