SIMS 213:
User Interface Design & Development
Marti Hearst
Thurs, Feb 12, 2004
Mental Models
People have mental models of how things work:
– how does your car start?
– how does an ATM machine work?
– how does your computer boot?
Allows people to make predictions about how
things will work
Based on slide by Saul Greenberg
Mental Models
Mental models built from
–
–
–
–
–
–
–
affordances
constraints
mappings
positive transfer
cultural associations/standards
instructions
interactions
Mental models are often wrong!
Based on slide by Saul Greenberg
Our mental models of how bicycles work
can “simulate” this to know it won’t work
Slide adapted from Saul Greenberg
People are always trying to
make sense of things
Mental models often extracted from fragmentary
evidence
People find ways to explain things
– Computer terminal breaks when accessing the
library catalog
– Certain you’re driving on the correct road
Norman’s Action Cycle
Human action has two primary aspects
– Execution: doing something
– Evaluation: comparison of what happened to what
was desired
Action Cycle
start here
Goals
Execution
Evaluation
The World
Action Cycle
start here
Goals
Execution
Evaluation
Intention to act
Evaluation of interpretations
Sequence of actions
Interpreting the perception
Execution of seq uence of actions
Perceiving the state of the world
The World
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 actions
Evaluation 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!
Example
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?
Based on slide by Saul Greenberg
Digital Watch Redesigned for Affordances
(Rachna Dhamija)
Digital Watch Redesigned for Affordances
(Ping Yee)
Interface Metaphors Revisited
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 tool
is like
a slide projector
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 system
Central 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)
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
move
my.doc
• inappropriate ones can be hidden
– generic commands
• the same type of action can be performed on the object
• eg drag ‘n drop:
Slide adapted from Saul Greenberg
Direct manipulation
Representation directly determines what can manipulated
Slide adapted from Saul Greenberg
Games
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”)
Slide adapted from 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
Based on slide by Saul Greenberg
Summary
Good Representations
– capture essential elements of the event / world
– deliberately leave out / mute the irrelevant
– appropriate for the user, their task, and their interpretation
Metaphors
– use our knowledge of the familiar and concrete to represent abstract concepts
– need not be literal
– have limitations that must be understood
Direct manipulation
– visibility of the objects of interest
– rapid, reversible, incremental actions
– manipulation by pointing and moving
– immediate and continuous display of results
Next Time
Raskin on Cognition
Modes
Cooper & Norman on Errors