Course Introduction;
Principles of Good Design
Professor Larry Heimann
Carnegie Mellon University
88-272 Lecture Notes — Fall 1999
Agenda
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Course Introduction & Overview
The Problems of Design
The Psychology of Users
Principles for User-Centered Design
Why Designers Go Astray
Course Business
• Welcome to 88-272
• Introduction of Professors
– Professor Peter Muhlberger
– Professor Larry Heimann
• Course Policies
– complete listing of course policies at website
– http://www.andrew.cmu.edu/course/88-272/index.html
– print out syllabus and first lab instructional material
Course Expectations & Overview
• Course Expectations
– What is this course supposed to be?
– What this course is not supposed to be
• Course Overview
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Begin with design and interface issues
Spend time on database issues and SQL
Move to web development via ASP and CGI
Return to usability and software processes
The Problems of Design
• The frustration of everyday life
– my problems using our cordless phone
– using my digital watch as a stop watch
– opening doors
• The need for good conceptual models
– my solution to the door opening problem
– example of freezer/refrigerator
Freezer/Refrigerator Controls
NORMAL SETTING
C AND
COLDER FRESH FOOD
C AND 6-7
1 SET BOTH CONTROLS
COLDEST FRESH FOOD
B AND 8-9
2 ALLOW 24 HOURS
COLDER FREEZER
D AND 7-8
WARMER FRESH FOOD
C AND 4-1
OFF (FRESH FD & FRZ)
0
A
B
C
D
FREEZER
E
5
TO STABILIZE
7
6
5
4
FRESH FOOD
3
A Conceptual Model of F/R
Freezer
Fresh Food
(w/ thermostat)
(w/ thermostat)
Freezer
Control
Cooling
Unit
Fresh FD
Control
Cooling
Unit
Correct Conceptual Model of F/R
Thermostat
Control A
Freezer
COLD AIR
Fresh
Food
Control B
Cooling
Unit
The Problems of Design
• The frustration of everyday life
– my problems with using our cordless phone
– using my digital watch as a stop watch
– opening doors
• The need for good conceptual models
– my solution to the door opening problem
– example of freezer/refrigerator
– conceptual models guide user actions; wrong
conceptual models leads to inexplicable errors
Design Problems…
(continued)
• The principle of mapping
– relationship between two things; in this case, between
the controls and results
– natural mapping takes advantage of physical analogies
and cultural standards (e.g., sound volume control)
– artificial mapping schemes may be necessary when no
obvious natural mapping scheme exists (e.g., gas range)
• The principle of feedback
– let users know condition of task in progress or
whether it has been successfully completed
– good feedback reduces user frustration and/or confusion
Trade-offs in Knowledge Location
Property
Knowledge in the world
Knowledge in the head
Retrievability
Retrievable whenever
visible or audible.
Not readily retrievable.
Requires memory search or
reminding.
Learning
Not required. Interpretation
substitutes for learning.
Ease of interpretation is a
function of ability to exploit
natural mappings and
constraints.
Required and can be
considerable. Learning
made easier if there is a
good mental model to guide.
Efficiency
of use
Slowed up by need to find
and interpret external
information
Can be very efficient.
Ease of use at
1st encounter
High.
Low.
Aesthetics
Maintaining a lot of
information can lead to
clutter and unaesthetic
designs (depending on skill
of designer
Nothing need be visible
which gives freedom to
designer to work on design
aesthetics
The Psychology of Users
• Falsely blaming yourself
– usability testing runs into problems: no one likes to be
watched because it makes them feel clumsy or stupid
– If an error occurs on a task that appears simple, people
tend to blame themselves -- not the design
• Misconceptions of everyday life
• Blaming the wrong cause
• Learned and taught helplessness
– people experience failure at a task; assume it can’t be done
– with poor design, it’s as if we teach people to be helpless
Errors Users Make
• Slips -- typically occurring when we are
distracted, tired, or stressed
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capture errors (driving a familiar route rather than correct route)
description errors (throwing dirty clothes in garbage, not hamper)
mode errors (digital watch in wrong mode for action)
data-driven errors (dialing phone number of room I’m in)
loss-of-activation errors (forgetting why I went to kitchen)
• Selective attention and the problem of focus
Errors…
(continued)
• Errors in different task structures
– wide and deep structures (chess)
– shallow structures (choosing ice cream flavor)
– narrow structures (cookbook)
• Social pressures and errors in judgment
– example of KAL 007 shot down over Soviet air space
– better design can sometimes (but not always!) help
reduce this type of error
– forcing functions may also be effective solutions
Execution and Evaluation
• The “Action Cycle” explained
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begin with goals: what we want to see happen
execution: what we do to the world
evaluation: comparing what happened to what we wanted
back to goals step; should they be revised?
• The gulf of execution -- the difference between
intentions and allowable actions.
• The gulf of evaluation -- the amount of effort
needed to determine how well results meet
expectations.
Principles of User-Centered Design
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Use both knowledge in world and in head
Simplify task structures
Narrow gulfs of execution & evaluation
Get mappings right
Exploit the power of constraints
Design for error
When all else fails, standardize
Why Designers Go Astray
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Ignorance
Put aesthetics first
Worship complexity
Designers forget they are not typical users
Identify the wrong group of users
Designers give way to “creeping featurism”