i
INF385P – Intro to Usability
Week 2 – Norman’s book and
mental models
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
1
I’m gonna go fast because . . .
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• It ain’t rocket science.
• You’ve already read the book.
• I’d rather make you scramble to keep up
than bore you.
• I have 80 slides I’m gonna do in 60 minutes
(yeah, right!).
– While I’m presenting this, see if you can
characterize your good and bad designs that
you’ve discovered this week in Norman’s
terms.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
2
Chapter 1
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• The PsychoPATHOLOGY of everyday
things
• Assumption: We blame ourselves for
errors, but the real culprit is faulty
design.
• Assumption: There’s nothing special
about computers. They have the same
sorts of design problems as simpler,
everyday things.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
3
Good Design
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• Well designed objects . . .
– are easy for the mind to understand
– contain visible cues to their operation
• Poorly designed objects . . .
– provide no clues, or
– provide false clues.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
4
Natural Signals
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• Natural signals lead to natural design.
• A metal plate “naturally” is to be pushed.
• Visible hinges “naturally” indicate
attachment, and that the other side
swings open. (And swings open
TOWARD me?)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
5
Mapping
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• Mapping is a relationship between two
things (e.g., between what you want to
do and what appears possible).
• Good design allows for a clear (visible)
mapping between . . .
– intended actions and
– actual operations.
• Now -- think of what this might mean in a
web site.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
6
Good Design
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• Principles of good design
– the importance of visibility
– appropriate clues
– feedback of ones actions.
• Just so you’ll know -- others have proposed
OTHER principles of good design. Go
check out the web site of Bruce Tognazzini:
http://www.asktog.com/basics/firstPrinciples.html
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
7
Affordance
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• Affordance is the perceived and actual properties of a
thing.
– Primarily those fundamental properties that
determine how a thing could possibly be used.
– “Affords” means, basically, “is for.”
– A chair affords support, therefore affords sitting.
• Affordances provide strong clues to things’ operations.
• When affordances are taken advantage of, the user
knows what to do just by looking.
– No label, picture, or instruction (“Push”) is required.
• - When simple things need pictures, labels, or
instructions,
the
design
has
failed.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
8
Complex World
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• 30,000 readily discriminable objects. How do we deal
with all of them?
– Partly, the way the mind works.
– Partly, the information available from the
appearance of objects.
– Partly, the ability of the designer to:
• make the operation clear,
• project a good image of the operation, and
• take advantage of the other things people might know.
• Here is where the designer’s knowledge of the
psychology of people coupled with the knowledge of
how things work becomes crucial.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
9
Principles of Design
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•
Four principles of Design for
Understandability and Usability.
1. Provide a good conceptual model.
– A good conceptual model allows us to
predict the effects of our actions.
– Simply knowing the relationship between
the controls and the outcomes.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
10
Principles of Design (cont’d.)
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2. Make things visible.
3. The principle of mapping.
– Natural mapping (taking advantage of
physical analogies and cultural standards)
leads to immediate understanding.
– Move the control up, the sound gets
louder.
– Seat adjustment in Fig. 1.13 is a good
example.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
11
Principles of Design (cont’d.)
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4. The principle of feedback.
– Feedback is sending back to the user
information about what action actually has
been done, what result has been
accomplished.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
12
The Paradox of Technology
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– Added functionality generally comes along
at the price of added complexity.
– The same technology that simplifies life by
providing more functions also complicates
life by making the device harder to learn
and use.
– The Paradox of Technology should never be
used as an excuse for poor design.
– Added complexity cannot be avoided when
functions are added, but with clever design
they can be minimized.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
13
Chapter 2 -- Psy of Everyday
Actions
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• Norman’s credo on errors -- if an error is
possible, someone will make it.
• The designer must design so as to:
– minimize the chance of errors in the first
place
– minimize the effects of an error
– make errors easy to detect
– make errors reversible, if possible.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
14
Models
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• Mental Models = our conceptual models of the way . . .
– objects work
– events take place
– people behave
• Mental models result from our tendency to form
explanation of things.
• Models are essential in helping us . . .
– understand our experiences
– predict the outcomes of our actions
– handle unexpected occurrences.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
15
Models (cont’d.)
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• We base our models on whatever knowledge we have:
– real or imaginary
– naïve or sophisticated
– even fragmentary evidence.
• Everyone forms theories (mental models) to explain
what they have observed.
• In the absence of feedback to the contrary, people are
free to let their imaginations run free.
• More on models in Chapter 3.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
16
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Blame
• People assign causal relation whenever two things
occur in succession.
• When we try something and fail, we blame ourselves
(especially when we know others have succeeded).
• Thus, a “Conspiracy of Silence,” leading to
– guilt
– helplessness
• Learned Helplessness
• Taught Helplessness
– Badly designed objects constructed so as to lead
to misunderstanding (faulty mental models). Think
of an internally inconsistent app or web site.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
17
7 Stages of Action
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•
On p. 47 is a series of four figures that
illustrate Norman’s view of the structure
of action.
• Actions have two major aspects:
1. Doing something (execution)
2. Checking (evaluation)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
18
7 Stages (cont’d.)
•
Action is broken down into 7 stages:
1.
2.
3.
4.
5.
6.
7.
Perceiving the state of the world
Interpreting the perception
Evaluating the interpretations
Setting a goal
Intention to act
Sequence of actions
Execution of actions
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
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7 Stages (cont’d.)
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• Specific actions bridge the gap between
– What we would like to do (goals and
intentions) and
– All possible physical actions.
• 7 stages form an “approximate model,”
not a complete psychological theory.
• One key -- continual feedback loop.
– Process can be started at any point.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
20
Gulfs . . .
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• Of Execution and Evaluation.
– Gulf of Execution -- the difference between
intentions and allowable actions.
– Gulf of Evaluation -- difficulty in interpreting
the physical state of a “system,” interpreting
how well the expectations and intentions
have been met.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
21
Designing
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• The 7-stage structure can be a valuable
design aid.
• Provides basic checklist of questions to
ask to ensure that
– the Gulf of Execution and
– the Gulf of Evaluation
are bridged.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
22
Designing (cont’d.)
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• There’s a question to ask for each stage
(see Fig. 2.7) and they boil down to the
principles of good design:
– visibility
– good conceptual model
– good mappings
– feedback.
• Next time you can’t immediately figure out
the shower control in a motel, remember
that the problem is in the design!
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
23
Chapter 3 - Knowledge in the
Head and in the World
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• Not all knowledge required for precise
behavior must be in the head. It can be
distributed:
– partly in the head
– partly in the world
– partly in the constraints of the world.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
24
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Knowledge
•
Precise behavior can emerge from
imprecise knowledge, because . . .
1. Information is in the world (e.g., signs).
2. Great precision is not required. (Not just one
path to school.)
3. Natural constraints are present. (Didn’t have
to worry about going UP as you drove to
school.)
4. Cultural constraints are present (e.g., driving
on the right).
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
25
Behavior
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• In everyday situations, behavior is
determined by the combination of . . .
– internal knowledge
– external info
– constraints.
• There’s a tradeoff between the amount
of mental knowledge and the amount of
external knowledge needed.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
26
In the world
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• An example.
• Typing:
– Letter names on keycaps.
– Requires that the typist look at keycaps.
– Goal of power typing is to get that
knowledge from the world into the head of
the typist.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
27
Knowledge OF and
Knowledge HOW
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• Knowledge OF = Declarative
Knowledge
– Knowledge of facts and rules
– Easy to write down, teach
• Knowledge HOW = Procedural Know.
– Difficult or impossible to write down, teach
– Best taught by demonstration and learned
through practice
– Largely subconscious
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
28
Constraints
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• The power of constraints -- the “memory” for epic poetry
is found to be mostly reconstruction, with the aid of the
constraints of rhyme, meter, etc.
• We use constraints to simplify what we must remember.
• For example, putting mechanical parts together.
– Some are constrained by what will and will not fit
together.
– Also cultural constraints -- screws tighten clockwise.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
29
Memory
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• . . . is knowledge in the head.
• Think of all you can remember. Phone
numbers, postal codes, passwords,
SSN, birthdays, etc., etc.
• It’s tough!
– So, we put memory in the world.
(Daytimers. Palm Pilots. Address books.
Stickies.)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
30
Memory Structure
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• Two major classes of memory: STM & LTM
• STM
– Memory of the just-present
– Retained automatically
– Retrieved without effort
– Limited capacity (7 +/- 2)
– Items easily bumped
– Capacity can be increased by chunking
– Items retained by rehearsal
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
31
Memory Structure (cont’d.)
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• LTM
– Memory for the past
– Storage and retrieval takes time
– Items stored according to interpretation (multikeyed indexing)
– Virtually unlimited capacity
– Storage and retrieval are easier when the
material makes sense
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
32
•
3 Categories of things
remembered
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Memory for arbitrary things, meaningful relationships,
memory through explanation
1. For arbitrary things:
– Rote learning
– Takes more time to encode
– When there’s a problem, memorized sequence of
events gives no hint of what’s gone wrong or how
to fix it.
– We impose structure or associations to help
• E.g., tune to help remember the alphabet
– Items aren’t understood. No mental model.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
33
3 Categories of things
remembered (cont’d.)
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2. Memory for meaningful relationships
– Enabled by mental models
– Interpretation is essential, but it is NOT
understanding.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
34
3 Categories of things
remembered (cont’d.)
3.
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Memory through explanation.
–
–
–
–
Most powerful form of internal memory
Mental models play a major role -- simplify learning because
the details can be DERIVED when needed.
• NOTE: The use of mental models to DERIVE behavior is not
ideal for tasks that must be done rapidly or smoothly.
Designers should provide users with appropriate models,
‘cause people make ‘em up, otherwise.
The power of mental models -- let you figure out what would
happen in novel situations.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
35
Memory . . .
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• . . . is also knowledge in the world.
• But only available when you are there.
(What if you don’t see that note you left
for yourself.)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
36
Reminding
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• A good example of the interplay between info in the
world and in your head.
• Strategies for reminding:
– Rehearsal
– Notes to self
– Put the burden on the thing to be remembered (put
the book by the door)
• Two different aspects of a reminder
– The signal (string around finger)
– The message (ring around finger)
• The ideal reminder has both components.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
37
In the World
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• Lots of products make it easier to put
knowledge in the world.
– Alarm clocks
– Diaries
– Calendars
– Watches
– PDAs
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
38
Natural Mappings . . .
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• . . . Reduce the need for information in
memory.
• Simple design principle:
If a design depends on labels, it may be
faulty.
Labels are important, and often necessary.
But the appropriate use of natural mappings
can minimize their need. (E.g., stove controls.)
Wherever labels seem necessary, consider
another design.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
39
Tradeoff . . .
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• . . . between info in the world and in the
head.
– Knowledge in the world acts as its own
reminder.
– Knowledge in the head is efficient. (You can
travel light.)
– Knowledge in the world is easier (no learn
time), but often difficult to use. Relies heavily
on the physical presence of info.
• See Fig. 3.6, p. 79.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
40
Ch. 4 -- Knowing what to do
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• When we encounter a novel object,
either
– We’ve dealt with something similar before,
and we transfer old knowledge, or
– We get instruction.
• Thus, information in the head.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
41
Design
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• How can the design of an object (NOTE:
info in the world) signal the appropriate
actions?
– Natural (physical) constraints
– Affordances, that convey messages about the
item’s possible uses, actions, and functions
• “The thoughtful uses of affordances and
constraints together in design lets a user
determine readily the proper course of
action even in a novel situation.”
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
42
Constraints - 4 Classes
•
•
•
•
i
Physical
Semantic
Cultural
Logical
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
43
Physical Constraints
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• Constrain possible operations
• Rely on properties of the physical world,
so no special training is required.
• Are made more effective and useful if
they are easy to see and interpret.
(Example: Glass over fire alarm.)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
44
Semantic Constraints
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• Rely on the meaning of the situation to
control the set of possible actions.
• Rely on our knowledge of the situation
and the world.
Example -- Windshield goes in front of
rider, in Legos!
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
45
Cultural Constraints
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• Signs are meant to be read.
• Guidelines for cultural behavior are
represented in the mind by schemas.
– Schemas are “knowledge structures that
contain the general rules and info necessary
for interpreting situations and for guiding
behavior.”
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
46
Logical Constraints
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• Logic dictates that all parts be used, and
fit together.
• Natural mappings work by providing
logical constraints.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
47
The Problem with Doors
i
• An example of applying affordances and constraints to
everyday objects.
• When we approach a door we expect to find some
visible signal.
– Tells us where to act
– Next step is to figure out how to act
– Sometimes we need a manual (a one-word manual)
– The proper hardware will operate a door smoothly
PLUS will indicate how the door is to be operated
• It will exhibit proper AFFORDANCES.
– Focus on aesthetics can blind the designer (and the
purchaser) to the lack of usability.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
48
The Problem with Switches
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• 2 fundamental problems
• Grouping problem (which switch goes with
which function)
– Controls that cause trouble should not be located
where they can be operated by accident.
– Solution -- separate the switches for two sets of
functions
– Another solution -- use different types of switches
– Combine the two solutions
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
49
The Problem with Switches
(cont’d.)
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• Mapping Problem (which switch goes
with which light)
– Unsolvable given current light switch design
(mismatch in spatial arrangement (horiz. vs.
vert.) makes a natural mapping impossible.
– Match the layout of the lights with the layout
of the switches.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
50
Visibility and Feedback
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• Visibility -- make relevant parts visible
• Feedback -- give each action an
immediate and obvious effect
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
51
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Using Sound for Visibility
• Sounds should be generated to give info about the
source
• Should convey something about the actions that are
taking place
• Natural sounds (not beeps) reflect the complex
interaction of natural objects
– The way one part moves against another
– The material of which the parts are made -- hollow
or solid, metal or wood, soft or hard, rough or
smooth
• One of the virtues of sounds is that they can be
detected even when attention is applied elsewhere.
But, thus, can be obtrusive.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
52
Ch. 5 - To err is human
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• Errors come in several forms
– Slips -- result from automatic behavior,
when subconscious actions get waylaid en
route (“performance errors”)
– Mistakes -- result from conscious
deliberations (“competence errors”)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
53
In terms of the 7 stages of
action . . .
i
• If you form an appropriate goal, but mess
up in the performance, you’ve made a
slip.
• If you form a wrong goal, you’ve made a
mistake.
• Slips are usually small things, relatively
easy to discover.
• Mistakes can be more major, harder to
detect. (Says Norman.)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
54
Slips
i
• Show up most often in skilled behavior.
(Does that seem contradictory? Think about it.)
• We don’t make many when we are still
learning.
• Result from lack of attention. (Or from a
speed-accuracy tradeoff.)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
55
Types of Slips
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• Capture errors -- a frequently done activity suddenly takes charge
instead of the intended one (e.g., typing THE instead of THY).
• Description errors -- the intended action has much in common
with others possible (e.g., turn on the wrong burner on stove).
• Data-driven errors -- automatic actions, triggered by the arrival of
some sensory data, intrude into an ongoing action sequence
(e.g., pick up the phone when you hear a ring on TV).
• Associative activation errors -- internal thoughts and associations
intrude, causing errors (e.g., think you’re leaving a phone
message for your wife, end with “I love you”).
• Loss-of-activation errors -- simply forgetting to do something
• Mode errors -- when devices have different modes of operation,
and the action appropriate for one mode has different meaning in
another mode (e.g., hitting the accelerator pedal when in neutral).
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
56
Modes
i
• Modes can be detected only if there is
feedback.
• Problem of level -- where (at what level
in the sequence) is the error?
• Problems of level constantly thwart the
correction of error.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
57
Design
i
• Design lessons from the study of slips.
– Don’t prevent errors by requiring
confirmation.
– Rather, eliminate irreversible errors.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
58
Mistakes
i
• Mistakes as errors of thought.
(Competence errors.)
• Mistakes result from the choice of
inappropriate goals.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
59
Three Models of Human
Cognition
1.
i
Photo Album Theory. (BUZZZ. Thank you for
playing.)
Schema Theory.
2.
–
–
–
Filing cabinet model
Lots of cross-references and pointers
Basic beliefs
• There is logic and order to individual structures (schema)
• Human memory is associative, with each schema pointing
and referring to multiple others (networked!)
• Much of the power for deductive thought comes from using
the info in one schema to deduce the properties of another.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
60
Third Approach -Connectionist
i
– Still unproven
– Less logical
– Each connectionist unit (whatever!) is connected to many
others
– Signals are either positive (activation) or negative
(inhibition)
– Thoughts = stable patterns of activity
– New thoughts are triggered by a change in the system
(from within or without) -- new info arrives and changes
the pattern of activation and inhibition
– Referred to as the “multiple exposure” theory of memory
– Good quote, p. 118, last para., through middle of p. 119.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
61
Tasks
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• The structure of tasks.
• Everyday structures are either shallow
and wide (ice cream list) or narrow and
deep (cookbook).
• Any task that involves a sequence of
activities where the action to be taken at
any point is determined by its place in
the sequence is “narrow.”
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
62
Tasks (cont’d.)
i
• Most tasks of daily life are routine.
Shallow or narrow.
• What are NOT everyday activities?
Those with wide or deep structures, that
require considerable conscious planning
and thought, deliberate trial and error.
(Did someone say surfing the web to find
some particular info?)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
63
Conscious and Subconscious
Behavior
i
• Much human behavior is done subconsciously
– without conscious awareness
– not available to introspection
• Subconscious thought matches patterns
– finding best match between past experience and
current needs
– proceeds rapidly, automatically, without effort
– good at generalizing
– but can find inappropriate matches
– a bias towards regularity and structure
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
64
Conscious Thought
i
– Slow and labored
– Ponder decisions, consider alternatives,
compare choices
– Slow and serial
– Limited by small STM
– Uses subconscious thought as a tool
– memory limitation is overcome by appropriate
organization structure
• Mistakes are made by mismatch -- by taking current
situation and falsely matching it with something in the
past.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
65
Designing for Error
i
• Everyone makes errors
• Designers make the mistake of not taking errors into
account
• Read p. 131 for list of what designers SHOULD do
• Forcing functions -- form of physical constraint
– Can’t put convertible top up or down unless the car is
in “park.”
• Read “A design philosophy,” p. 140.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
66
Ch. 6 -- The Design Challenge
i
• Norman talks about what forces work
against evolutionary, or natural design
(pp. 142-143).
– The demands of time (quick product cycles)
– The pressure to be distinctive (related to the
curse of individuality)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
67
Typewriter - Case History
i
• Note the important design lesson on p.
150.
• To wit: Once a satisfactory product has
been achieved, further changes may be
counterproductive.
– (What does that have to say about web site
design.)
• Norman says you have to know when to
stop.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
68
Pitfalls
i
•
Three reasons why designers go
astray:
1. Putting aesthetics first
2. Designers aren’t typical users
3. Designers’ clients may not be the users
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
69
Complexity of the Design
Process
i
• Not a lot of meat in this chapter
• Understand the concepts of
– selective attention
– the problem of focus
• Understand the “two deadly temptations
for the designer”
– creeping featurism
– worshipping false images (e.g., complexity)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
70
Finally . . .
i
• . . . toward the end of the chapter (about
p. 177) he starts getting into computer
systems.
• That’s a pointer to our final projects.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
71
Ch. 7 - UCD
i
• Chapter 7 is the “punch line” of the whole
book.
• User-Centered Design
• Most of the chapter is given over to
describing “seven principles for
transforming difficult tasks into simple
ones.”
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
72
Principle 1
i
• Use both knowledge in the world and
knowledge in the head.
• Here Norman refers to his distinction
between the mental models of the
designer and the user, and the
relationship between these and the
actual system.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
73
Principle 2
i
• Simplify the structure of tasks
• Here Norman recalls our discussion of STM and LTM,
and their different weaknesses. He also offers 4 “major
technological approaches” that “can make the
mappings more visible or, better, more natural.”
– 1 Keep the task much the same, but provide mental
aids.
– 2 Use technology to make visible what would otherwise
be invisible, thus providing feedback and the ability to
keep control.
– 3 Automate, but keep the task much the same.
– 4 Change the nature of the task.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
74
3, 4, 5
i
• Principle 3 -- Make things visible: Bridge
the Gulfs of Execution and Evaluation.
• Principle 4 -- Get the mappings right.
• Principle 5 -- Exploit the power of
constraints, both natural and artificial.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
75
6 and 7
i
• Principle 6 -- Design for error. Assume
that any error than can be made will be
made.
• Principle 7 -- When all else fails,
standardize.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
76
Etc.
i
• He goes on to offer a section on why you
might want to design something to be
hard to use ON PURPOSE.
• And he ends with a few sections on
writing, the home of the future, and a
concluding section.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
77
Next . . . your homework
i
• Bad designs.
• Good designs.
Famous quote: “No one ever raised a statue to
a critic.” Sibelius
I want us all to remember that it is easier to
criticize another design than it is to design
something.
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
78
Now . . .
i
• Let’s try to put it in Norman’s terms why
the good designs were good and the bad
designs were bad. (“Some important
feature was, or was not, visible.”)
R. G. Bias | School of Information | SZB 562B | Phone: 512 471 7046 | rbias@ischool.utexas.edu
79