SIMS 213: User Interface Design &

Development

Marti Hearst

Thurs, Feb 1, 2001

Cooper Chapter 11

Scenarios– Daily use vs Edge Case

Perpetual Intermediaries The Importance of Precise Vocabulary Case study: Image processing tool

– Who are the Personas? Found some common goals Focus on a few key capabilities Matched to the capabilities of the system

– Had fewer features, but seemed most powerful!

Cognitive Considerations

From Don Norman’s book, The Psychology (Design) of Everyday Things– Affordances, Constraints, and Mappings– Mental Models– Action Cycle and Gulf of Execution

Based on slide by Saul Greenberg

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!

Slide adapted from Saul Greenberg

Our mental models of how bicycles workcan “simulate” this to know it won’t work

Slide adapted from Saul Greenberg

People are always trying to explain things

Mental models often extracted from fragmentary evidence

People find ways to explain things– Computer terminal breaks when accessing the

library catalog– Sure your driving on the correct road

Norman’s Action Cycle

Human action has two aspects– execution and evaluation

Execution: doing something Evaluation: comparison of what happened to

what was desired

Action Cycle

Goals

EvaluationExecution

The World

start here

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 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!

Based on slide by Saul Greenberg

Good 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

Digital Watch Redesigned for Affordances (Rachna Dhamija)

Digital Watch Redesigned for Affordances (Ping Yee)

Slide adapted from Saul Greenberg

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 toolis like

a slide projector

Slide adapted from Saul Greenberg

Interface Metaphors

– Use metaphors that matches user's conceptual task – desktop metaphor for office workers– paintbrush metaphor for artists...

– Given a choice, choose the metaphor close to the way the system works

– Ensure emotional tone is appropriate to usersE.g., file deletion metaphors

– trashcan– black hole– paper shredder– pit bull terrier– nuclear disposal unit...

Slide adapted from Saul Greenberg

Metaphors continued

metaphors can be overdone! Common pitfalls

– overly literal unnecessary fidelity excessive interactions

– overly cute novelty quickly wears off

– overly restrictive cannot move beyond

– mismatched does not match user’s

task and/or thinking

Slide adapted from Saul Greenberg

The Metaphor of Direct Manipulation

Direct Manipulation– the feeling of working directly on the task– 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)

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

Phone list

List metaphor Rolodex metaphor

Slide adapted from Saul Greenberg

Games

Slide adapted from Saul Greenberg

Direct Manipulation

Xerox Star: pioneered in early '80s, copied by almost everyone– simulates desktop with icons

in and out baskets file folders and documents calculators printers blank forms for letters and memos

– small number of generic actions applicable system wide move, copy, delete, show properties, again, undo, help

– eg same way to move text, documents, etc property sheets

– pop-up form, alterable by user

– What you see is what you get (WYSIWYG)

Slide adapted from Saul Greenberg

Xerox Star continued

Star's observers:– objects understood in terms of their visual characteristics

affordances, constraints

– actions understood in terms of their effects on the screen causality

– intuitively reasonable actions can be performed at any time conceptual model

A subtle thing happens when everything is visible: the display becomes reality

Slide adapted from Saul Greenberg

Is direct manipulation the way to go?

Some Disadvantages– Ill-suited for abstract operations

spell-checker?

– Tedium manually search large database vs query

– Task domain may not have adequate physical/visual metaphor

– Metaphor may be overly-restrictive

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

Conventional Applications: A Mix

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

Slide adapted from Saul Greenberg

Summary

Good Representations– captures essential elements of the event / world– deliberately leave out / mute the irrelevant– appropriate for the targetted users, 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

Raskin on Cognition

Cognitive Engineering– Ergonomics: sizes and capabilities of the human

body– Cognetics: Ergonomics of the mind– Applied side of cognitive science

Image from Newsweek, Jan 2001

Raskin on Cognition

Cognitive Conscious / Unconscious– Examples?– Differences?

Locus of Attention– What is it?– Why is it important for HCI?

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

Inane Dialog Boxes

Slide adapted from Saul Greenberg

Silly Help

Midwest Microwave's online catalog

ClearCase, a source-code control system from Rational Software

Slide adapted from Saul Greenberg

“HIT ANY KEY TO CONTINUE”

Next Time: Design