COMP 3715 Spring 05

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COMP 3715 Spring 05
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Computer Interface

• Interaction between human and computer
• Has to deal with two things
• Users mental model
• Different user has different models
• The state of the computer
• Need to adapt to different users need

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Interface design principles

• Naturalness
• Consistency
• Relevance
• Supportiveness
• Flexibility

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Naturalness

• Intuitive to user
• Natural language
• Minimize IT jargon
• But jargon related to the task ok
• Instructional, not personal
• Self-explanatory
• Minimize human pre/post-process
• Need to adopt to user

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Consistency

• Input format
• Output format
• Menu layout
• Messages
• No surprises!

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Relevance

• No redundancy
• Minimize required input
• Key strokes
• Minimize required information
• Minimize output messages
• Unnecessary information
• Irrelevant information scare users

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Supportiveness

• Need adequate information to user
• Enough feedback to user
• Need to determine the users need
• Novice vs. Expert

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Flexibility

• Need to accommodate differences
• User preference
• User requirement
• User expertise
• Personalization
• But, more personalization less help among users
• Need a way to restore and remember

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Interaction style command language

• E.g. DOS prompt, UNIX prompt
• Typically restricted language set (list of
  commands)
• Commands with modifiers/parameters
• Advantages
• Flexibility
• Speed for expert users
• Feeling of control
• Disadvantages
• Non-supportive
• Not necessarily natural

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Interaction style command language

• Design questions
• What should be the legal command?
• Long form vs. abbreviation
• Error messages need to be supportive
• Hierarchy of commands?
• Learning curve

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Interaction style

• Graphical user interface
• Question and answer
• Menu
• Form

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Interaction style -- GUI

• Question and answer
• System ask question, user answers, system decide
  what to do next
• Answer can be in different formats
• Choices radio buttons, acceptable characters
• Free form
• Advantages
• Moderately supportive
• Flexible short-cuts, various input types
• Disadvantages
• Can be tedious if not careful
• Problem of irrelevancy magnified

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Interaction style -- GUI

• Question and answer

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Interaction style -- GUI

• Question and answer
• Design issues
• Need careful planning of dialog
• Avoid getting stuck in loops
• Dont ask the same thing twice unless necessary
• Default is useful
• Nicely designed, good for novices

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Interaction style -- GUI

• Menus
• Various types
• Bars
• Block
• Button
• Full screen
• Pop-up, tear-off
• Cascade menus
• System dictates what can be input next
• Advantage
• Supportive clear signal of what to input next
• Disadvantage
• Less flexible amount of input limited
• Multiple selection can be cumbersome
• What if user want to select nothing?

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Interaction style -- GUI

• Menus
• Design decisions
• 7?2 rules avoid too many items on menus
• Also make novice hard to choose
• Naming menus
• Unify menus if possible
• Board vs. Deep menus
• Ordering of menu items
• Frequency vs. Alphabetical vs. Categorical vs.
  Conventional

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Interaction style -- GUI

• Forms
• A predefined sequence
• User cannot move-on until all parts of form
  filled
• Auto-skip feature to move to the next input
• Advantage
• Supportive very clear directives
• Disadvantage
• Non-flexible

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Interaction style -- GUI

• Forms
• Design issues
• Ordering/Division of requests
• Next step
• When to check for errors

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Issues in GUIs

• Use of metaphors
• Process drag and drop mimics moving
• Symbols icons represent objects/tasks
• E.g. of iconic interfaces
• Desktop
• Paintbox
• Spreadsheet

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• Why icons
• Metaphor mimic reality comfort for users
• Easy to learn
• Easy to retain knowledge
• Good feedback available

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• Limitations
• Possibility of confusion
• Meaning of icons
• Meaning of action
• Selection vs Dragging
• Single-click vs. double-click
• Lack of flexibility

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Guideline in designing GUI for human need

• Need to concern about human responses
• Reaction time
• Movement time
• Attention
• Selective attention
• Focused attention
• Divided attention
• Sustained attention

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• Reaction time
• Typically 200ms
• Longer if unexpected
• Longer for young and old
• Longer if periphery vision
• Movement time
• Movement speed varies for different
  directions/part of body

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• Selective attention
• Monitoring multiple channels
• watch two windows
• Listen and watch
• Memory limitation
• 7?2 principle
• Stressful less attention
• Design notes
• Need to be clear about importance of each channel
• Should avoid surprises (let user know what will
  likely to happen next)
• Channels should be close together

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• Focused attention
• Attention to a single channel without distraction
• Typing on the WordPad while other things are
  happening
• Design guidelines
• Channel of interests should demand attention
• Competing channels should be far apart
  distinct

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• Divided attentions
• Attempting to do multiple things at once
• Design guidelines
• Tasks should be easy
• Allow prioritization