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Usability Principles
Concepts, Principles, Guidelines Fall 2008 PSYCH / CS 6750^2
Agenda
Usability Principles Why? Systems of categorization Levels of detail Example system of Principles Fall 2008 PSYCH / CS 6750 3
Good Design (our goal!)
“Every designer wants to build a high- quality interactive system that is admired by colleagues, celebrated by users, circulated widely, and imitated frequently.” (Shneiderman, 1992, p.7) …and anything goes!… Fall 2008 PSYCH / CS 6750 4
Why Principles & Guidelines?
…Because, well, not everything goes… Intended to prevent many bad designs, before they begin, or evaluate existing designs on a scientific basis Guidelines based on previous designs, experimental findings Rules can all be “broken” (but usually in order to satisfy another principle)
Fall 2008 PSYCH / CS 6750^5
Concepts, Principles, Guidelines
No “cookbooks” No simple, universal checklists There are many concepts, principles, and guidelines Understand the higher level principles that apply across situations, display types, etc. Implement the standards and guidelines …a few details… Fall 2008 PSYCH / CS 6750^6
Levels of Consideration
- Meta-display level Apply to the whole system, across media & across displays Focus on this in Basic Layout Stage
- Display Layout Apply to groups of elements in a display Focus on this in Prototyping and Redesign
- Element level Details about specific parts of a display Colors, sound attributes, symbols Fall 2008 PSYCH / CS 6750 7
UI Design Principles (Dix et al.)
Categories
- Learnability
- support for learning for users of all levels
- Flexibility
- support for multiple ways of doing tasks
- Robustness
- support for recovery Think about these in terms of meta- display, display, and element levels Fall 2008 PSYCH / CS 6750 8
1. Learnability Principles
Ease with which new users can begin effective interaction and achieve maximal performance Predictability Synthesizability Familiarity Generalizability Consistency
Fall 2008 PSYCH / CS 6750^13
Generalizability
Can knowledge of one system/UI be extended to other similar ones? Example: cut & paste in different applications Does knowledge of one aspect of a UI apply to rest of the UI?
- e.g. file browser in OS, file locater in MS-Word Aid: UI Developers guidelines Fall 2008 PSYCH / CS 6750^14
Consistency
Likeness in behavior between similar tasks/operations/situations In different things
- interacting
- output
- screen layout Is this always desirable for all systems, all users? Fall 2008 PSYCH / CS 6750 15
2. Flexibility Principles
Multiplicity of ways that users and system exchange information Dialog Initiative Multithreading Task migratability Substitutivity Customizability Fall 2008 PSYCH / CS 6750 16
Dialog Initiative
Not hampering the user by placing constraints on how dialog is done User pre-emptive
- User initiates actions
- More flexible, generally more desirable System pre-emptive
- System does all prompts, user responds
- Sometimes necessary
Fall 2008 PSYCH / CS 6750^17
Multithreading
Allowing user to perform more than one task at a time Two types Concurrent
- Input to multiple tasks simultaneously Interleaved
- Many tasks, but input to one at a time Fall 2008 PSYCH / CS 6750^18
Task migratability
Ability to move performance of task to entity (user or system) who can do it better Auto-pilot/FMC in planes Spell-checking Safety controls in plant For what kinds of tasks should the user be in control? Fall 2008 PSYCH / CS 6750 19
Substitutivity
Flexibility in details of operations Allow user to choose interaction methods Allow different ways to
- perform actions
- specify data
- configure Allow different ways of presenting output
- to suit task, user Fall 2008 PSYCH / CS 6750 20
Customizability
Ability of user to modify interface By user - adaptability
- Is this a good thing? By system - adaptivity
- Is this a good thing?
Fall 2008 PSYCH / CS 6750^25
Task Conformance
Does system support all tasks user wishes to perform in expected ways? Task completeness
- Can system do all tasks of interest? Task adequacy
- Can user understand how to do tasks? Does it allow user to define new tasks? Fall 2008 PSYCH / CS 6750^26
And Don’t Forget Comfort!
Fall 2008 PSYCH / CS 6750 27
Application of Principles
In doing design and implementation of your project, revisit this list Assess your design against these usability principles REMEMBER: There are other principles! (see the end of this lecture’s slides) Fall 2008 PSYCH / CS 6750 28
Project
Web space Group finalizing Help getting general topic area Reminder: IRB Online Training Assignment
Fall 2008 PSYCH / CS 6750^29
Upcoming
Human Capabilities Physical Cognitive Project team & topic due soon! Fall 2008 PSYCH / CS 6750^30
Some Practical Principles
The following pages contain a number of different, practical guidelines at each of the three levels (meta, display, and element levels) Some are the same or similar to ones we have discussed in class Some are more specific They have proven useful to me, but, of course, your mileage may vary Fall 2008 PSYCH / CS 6750 31
Meta-display Principles, I
Navigation model Decide on one navigation metaphor (e.g., menu structure vs. home page), and use it consistently. Consistent navigation cues Families of logos, color schemes, and sounds used to indicate displays are related. Be subtle, consistent, and don’t forget aesthetics! Fail-safe design principle Allow user to go back to previous items, steps, screens, etc. Allow user to undo as many actions as possible. Provide a true “Quit” or “Cancel” option. Fall 2008 PSYCH / CS 6750 32
Meta-display Principles, II
Open-ended vs. Task completion model Distinguish between browsing (open-ended) interaction, and task completion behavior. Concert vs. Conversation model A continuum of interaction types from passive recipient of the information (“concert”) to ask-and-respond dialog between the user and the system (“conversation”). Computer vs. Appliance model May need to avoid “computerese” and jargon.
Fall 2008 PSYCH / CS 6750^37
Element Level Guidelines, I
- A few “controls” guidelines… Label-Action match Controls say what they do, and do what they say. Consistent both within and across applications. Note: “OK” is not okay! Button location / icon /action compatibility (1) Control icon is compatible with action (2) Control location is compatible with the action (and with the icon) Consistent menus Menus should be consistent within and across applications. Most frequently used options located to the top and left. Fall 2008 PSYCH / CS 6750^38
Element Level Guidelines, II
- Several auditory guidelines… Duration: 100 ms minimum Loudness: 10-15 dB over ambient; max 90 dB Onset (“attack”) rate: 1-5 dB per second; 20 ms minimum Frequency: 300 - 3000 Hz. Varies with age. Levels of data in a dimension: Intensity (pure tones) 4- Frequency 4- Duration 2- Fall 2008 PSYCH / CS 6750 39
Element Level Guidelines, III
- More auditory guidelines… Appropriate spectrum Complex spectral features for warning or detection; transients for localization; simple spectrum for discrimination Avoid similar frequencies (Leads to “beating”, poor discrimination) Use population expectancies for mappings Louder, brighter, faster, higher pitch = “more” or “up” Rising pitch = “moving up” or “getting full” Major key, bright spectrum = “happy” or “good” Note: Make sure you know which population stereotypes apply (e.g., sighted vs. blind listeners)
