Jan 20, 2011 IAT 334 1

IAT 334Interface Design

Cognitive Aspects (Review)Usability Principles______________________________________________________________________________________

SCHOOL OF INTERACTIVE ARTS + TECHNOLOGY [SIAT] | WWW.SIAT.SFU.CA

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Agendag Cognitive Processes

– Implications– Motor system

g Usability Principles– Learnability Principles– Flexibility Principles– Robustness Principles

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Basic HCIg Model Human Processor

– A simple model of human cognition– Card, Moran, Newell 1983

g Components:– Senses – Sensory store– Short-term memory– Long-term memory– Cognition

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Model Human Processor Basicsg Based on Empirical Datag Three interacting subsystems

– Perceptual (read-scan)– Cognitive (think)– Motor (respond)

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Information Processingg Usually serial action

– Respond to buzzer by pressing button g Usually parallel recognition

• Driving, reading signs, listening to radio

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Processesg Four main processes of cognitive

system:– Selective Attention– Learning– Problem Solving– Language

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Selective Attentiong We can focus on one particular thing

– Eg cocktail party talk

g Salient visual cues can facilitate s.a.– Examples?– Bold, Larger fonts

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Learningg Procedural Learning:

– How to do somethingg Declarative Learning:

– Facts about somethingg Involves

– Memorization– Understanding concepts & rules– Acquiring motor skills– Automization

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Learningg Facilitated

– By analogy– By structure & organization– If presented in incremental units– Repetition

g Use user’s previous knowledge in interface– Hence, I hate PowerPoint 07!

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Observationsg Users focus on getting job done, not

learning to effectively use system

g Users apply analogy even when it doesn’t apply– Mac Trashcan for disk eject

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Problem Solvingg Storage in LTM, then applicationg Reasoning

– Deductive- If P then Q, P

– Inductive- If P then Q, Q

– Abductive- Generalization

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Observationsg People are more heuristic than

algorithmic

g People often choose suboptimal strategies for low priority problems

g People learn better strategies with practice

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Implicationsg Allow flexible shortcuts

– Forcing lengthy, mechanistic plans on user will bore them

– Quick Keys! ALT-Q to Quitg Have active rather than passive help

– Recognize waste

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Languageg Rule-based

– How do you make plurals?g Productive

– We make up sentencesg Key-word and positional

– Patterns

g Should systems have natural language interfaces?

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Peopleg “Good”

– Infinite capacity LTM– LTM duration & complexity– High-learning capability– Powerful attention mechanism– Powerful pattern recognition

g “Bad”– Limited capacity STM– Limited duration STM– Unreliable access to LTM– Error-prone processing– Slow processing

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Recapg I. Senses

– A. Sight– B. Sound– C. Touch

g 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 Principlesg Categories

– Learnability• support for learning for users of all levels

– Flexibility• support for multiple ways of doing tasks

– Robustness• support for recovery

g Always think about exceptions, suitability

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Learnability Principlesg Predictabilityg Synthesizabilityg Familiarityg Generalizabilityg Consistency

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Predictabilityg I think that this action will do…

g Operation visibility - can see avail actions– e.g. menus vs. command shell– grayed menu items

Predictable?

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Synthesizabilityg 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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Familiarityg 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?

Familiarityg What does the blinking green traffic

light mean in Ontario?

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Generalizabilityg Does knowledge of one UI apply to

others?– Cut and paste in many apps

g Does knowledge of one aspect of a UI apply to rest of the UI?– File browsers in MacOS/ Windows

g Aid: UI Developers guidelines

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Consistencyg Similar ways of doing tasks

– interacting– output– screen layout

g Is this always desirable for all systems, all users?

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Flexibility Principlesg Dialog Initiativeg Multithreadingg Task migratibilityg Substitutivityg Customizability

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Dialog Initiativeg System pre-emptive

– system does all prompts, user responds• sometimes necessary• Eg. Bank machine

g User pre-emptive– user initiates actions

• more flexible

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Multithreadingg Two types

– Concurrent • input to multiple tasks simultaneously

– Interleaved• many tasks, but input to one task at a time

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Task migratabilityg 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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Substitutivityg 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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Customizabilityg Ability to modify interface

– By user - adaptability

– By system - adaptivity

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Robustness Principlesg Observabilityg Recoverabilityg Responsivenessg Task Conformance

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Observabilityg 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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Recoverabilityg 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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Responsivenessg 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 Conformanceg Task coverage

– can system do all tasks of interest?

g Task adequacy– Can user do tasks?– Does system match real-world tasks?