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Review Affordances, Mappings, Mental ModelsNorman’s Action CycleMetaphors in InterfacesRaskin’s Locus of AttentionError Messages
Based on slide by Saul Greenberg
Putting These Together
Scissors– affordances:
• holes for insertion of fingers• blades for cutting
– constraints• big hole for several fingers, small hole for thumb
– mapping• between holes and fingers suggested and constrained by appearance
– positive transfer• learnt when young
– conceptual model• implications clear of how the operating parts work
Based on slide by Saul Greenberg
Bad Example
Digital Watch– affordances
• four push buttons, not clear what they do– contraints and mapping unknown
• no visible relation between buttons and the end-result of their actions– negative transfer
• little association with analog watches– cultural standards
• somewhat standardized functionality, but highly variable– conceptual model
• must be taught; not obvious
How to design a better one?
Norman’s Action Cycle
Human action has two primary aspects– Execution: doing something– Evaluation: comparison of what happened to what
was desired
Action Cycle
Goals
EvaluationEvaluation of interpretations
Interpreting the perception
Perceiving the state of the world
ExecutionIntention to act
Sequence of actions
Execution of seq uence of actions
The World
start here
Norman’s Action Cycle
Execution has three stages:– Start with a goal– Translate into an intention– Translate into a sequence of actions
Now execute the actionsEvaluation has three stages:– Perceive world– Interpret what was perceived– Compare with respect to original intentions
Gulf of Evaluation
The amount of effort a person must exert to interpret – the physical state of the system– how well the expectations and intentions have been
met
We want a small gulf!
Slide adapted from James Landay
Metaphor
Lakoff & Johnson– “...the way we think, what we experience, and what we do
every day is very much a matter of metaphor.'' – in our language & thinking - “argument is war”
• …he attacked every weak point ... criticisms right on target ... if you use that strategy
We can use metaphor to highlight certain features & suppress others– There is some systematicity to the transference
Interface Metaphors
Definition of Metaphor– application of name or descriptive term to an object to which it is not
literally applicable
Purpose– function as natural models – leverages our knowledge of familiar, concrete objects/experiences to
understand abstract computer and task concepts
Problem– metaphor may portray inaccurate or naive conceptual model of the system
A presentation toolis like
a slide projector
The Desktop MetaphorStarted at Xerox PARC – Xerox Star (see video)– Bitmapped screens made it possible
Not meant to be a real desktop– Idea is to organize information in a way to allow people to use it in the way they
user information on their desktops– Allow windows to overlap – make the screen act as if there were objects on it
Apple took it farther– Waste basket, etc
Microsoft took it to extremes– Microsoft Bob – a recognized failure
Beyond the Desktop
Robertson, George et al. "The Task Gallery: A 3D Window Manager." In Proceedings of CHI 2000
Beyond the Desktop
Jun Rekimoto, Multiple-Computer User Interfaces: "Beyond the Desktop" Direct Manipulation Environments, ACM CHI2000 Video Proceedings, 2000.
Identify the mis-matched metaphors(from the Interface Hall of Shame)
The classic (from the mac desktop)– To eject a disk you drag it to the trashcan
Identify the mis-matched metaphors(from the Interface Hall of Shame)
VCR buttons to control a printer??
Identify the mis-matched metaphors(from the Interface Hall of Shame)
Using tabs to make arbitrary groups
The Metaphor of Direct Manipulation
Direct Engagement– the feeling of working directly on the task
Direct Manipulation– An interface that behaves as though the interaction was with a real-world
object rather than with an abstract systemCentral ideas– visibility of the objects of interest– rapid, reversible, incremental actions– manipulation by pointing and moving– immediate and continuous display of results
Almost always based on a metaphor– mapped onto some facet of the real world task semantics)
Direct Manipulation uses a Metaphor
Metaphor– Computer objects as visible, moveable objects
Consequences– Items represented as icons– Items can be “picked up” and “moved” on a surface– Items can be “thrown out”– Items can be “copied”
• Do we really want to have to drag them to a photocopier?
How much is too much?
Slide adapted from Saul Greenberg
Object-Action vs Action-Object
Select object, then do action– interface emphasizes 'nouns' (visible objects) rather than 'verbs' (actions)
Advantages– closer to real world– modeless interaction– actions always within context of object
• inappropriate ones can be hidden– generic commands
• the same type of action can be performed on the object• eg drag ‘n drop:
my.doc
move
Slide adapted from Saul Greenberg
Direct manipulation
Representation directly determines what can manipulated
Slide adapted from Saul Greenberg
Is direct manipulation the way to go?
Some Disadvantages– Ill-suited for abstract operations
• Spell-checker?
• Search database by scrolling or by query?
Solution: Most systems combine direct manipulation and abstractions
• Word processor:– WYSIWYG document (direct manipulation)– buttons, menus, dialog boxes (abstractions, but direct manipulation “in
the small”)
Guidelines for Design
Metaphors– use our knowledge of the familiar and concrete to represent
abstract concepts– need not be literal– have limitations that must be understood
Based on slide by Saul Greenberg
Guidelines for Design
Provide a good conceptual model– allows users to predict consequences of actions– communicated thorugh the image of the system
Make things visible– relations between user’s intentions, required actions, and
results should be• sensible• consistent• meaningful (non-arbitrary)
– make use of visible affordances, mappings, and constraints– remind person of what can be done and how to do it
Guidelines for Design
Good Representations• capture essential elements of the event / world• deliberately leave out / mute the irrelevant• appropriate for the user, their task, and their interpretation
Raskin on Cognition
Cognitive Engineering– Ergonomics:
• Takes into account the statistical variation of human variability– Design a car seat that fits 95% of the population
• Says that designing products that interact with us physically is reasonable straightforward
– Cognetics: Ergonomics of the mind• The study of the “engineering scope of our mental abilities”
– This is the applied side of cognitive science
Image from Newsweek, Jan 2001
Raskin on Cognition
Cognitive Conscious / Unconscious– Examples?
• What is the last letter in your first name?– You know it but weren’t consciously accessing this information a
moment ago, but now you are.• How do your shoes feel right now?• How did “The Shining” make you feel?• Having a name on the “tip of your tongue”
– Differences?• New situations/routines• Decisions / one standard choice• Sequential / simultaneous
Image from Newsweek, Jan 2001
Raskin on Cognition
Locus of Attention– What is it?
• An idea/object/event about which you are intently and actively thinking.
• The one entity on which you are currently concentrating– You see and hear much more– E.g., white noise
» Turn the lights off, you have a full-fidelity recording of their sound in your mind, which fades quickly
– Why locus?• Focus implies volition; locus not always under conscious control• Attention can be either active or “going with the flow”
Raskin on Cognition
Locus of Attention– Why is it important for HCI?
• Cannot be conscious of more than one task at a time• Make the task the locus of attention
– Don’t count on people to read labels or directions• Beware of the power of mental habits
– Repetitive confirmations don’t work• Take advantage of it
– Do pre-loading while user thinking about next step– Streamline resumption of interrupted tasks
Cooper on error dialog boxes
Why are they problematic?How related to locus of attention?What are the alternatives?– Cooper is talking to programmers
• “Silicon Sanctimony”• You should feel as guilty as for using a goto – an
admission of failure in design
What happens when you cancel a cancelled operation?
Do I have any choice in this?
Umm, thanks for the warning,but what should I do?
Uhhh… I give up on this one