Introduction to Usability
Engineering
Laura Leventhal and Julie Barnes
1
Sources
 Chapter
1, Protobook
2
Motivation for this Unit
 When
you are finished with the introduction
(lectures 1 - 3), you should be able to :
•
Look at an object or a system that you have in your
home. Separate the functional components of that
system from the interface.
 View
a technology in a magazine, in real life or in a
museum. Reflect on where that technology fell in
the historical development of similar technologies.
3
Everyday Things Have a User
Interface
 Ken
Olsen, founded and CEO of Digital
Equipment, confessed that he can't figure out how
to heat coffee in the company’s microwave.
 POET stands for Psychology of Everyday Things.
This book is by Don Norman.
 The book contains many different examples of
poorly designed everyday objects. It also
discusses how the design process could be altered
to ensure better design.
4
Some everyday examples:
 Figure
1.1 coffee pot overhead
 "If I were placed in the cockpit of a modern
day jet airliner my inability to perform
gracefully and smoothly would neither
surprise nor bother me. But I shouldn't have
trouble with doors and switches, taps and
cookers (Norman, 1988, p. 2).
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More examples
–
–
–
A friend told me of the time he got trapped in the doorway of a post office in a European city.
The entrance was an imposing row of perhaps six glass swinging doors, followed immediately
by a second, identical row. That's a standard design - it helps reduce the airflow and maintain
the indoor temperature of the building.
My friend pushed on the side of one of the leftmost pair of outer doors. It swung inward and he
entered the building. Then before he could get to the next row of doors he was distracted and
turned around for and instant. He didn't realize it at the time, but he had moved slightly to the
right. So when he came to the next door and pushed it nothing happened. "Hmmm," he
thought, "must be locked." So he pushed the side of the adjacent door. Nothing. Puzzled my
friend decided to go outside again. He turned around and pushed the door. Nothing. He tried
the adjacent door. Nothing. The door he had just come in through no longer worked. He
turned around once more and tried the inside doors again. Nothing. Concern to mild panic....
he was trapped! Just then a group of people on the other side of the entrance way (far to the
right) passed easily through both sets of doors. My friend hurried over and followed them
through.
How could such a thing happen? A swinging door has two sides. One is pillar and hinge, the
other moves. To open the door one must push the moveable side. Pushing on the hinges has no
effect. In this case, the designed had aimed for beauty, not utility. No distracting lines, no
visible pillars, no visible hinges. So how can you tell which side to push?
6
More examples
 Computer
Disks - old floppy can go in any
way/ small floppy only one way. Why - it is
not really square! It is slightly rectangular.
 CS department, ergonomically correct chair.
Can anyone adjust it?
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Conclusions from these
examples:




Everyday devices have an interface, or boundary between
device and user, which can be good, ok or terrible.
As we will learn in this course, software interfaces, like
everyday devices can be good, ok or terrible.
Principles that assist in the design of usable everyday
objects are useful to consider when designing software
interfaces.
Heightened awareness of good vs. poor design of everyday
devices makes us better evaluators of software interfaces.
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How are we able to use
everyday objects like doors?
 Objects
and their user interfaces give us
subtle clues as to how to operate the
interface.
 From experience, we recognize and
interpret these clues.
 For example, the location and shape of a
door knob may give us clues as to
whether to push the knob or to turn it
– The location and shape of a door knob may give us
clues as to whether to push the knob or to turn it.
– If in public buildings and wish to get out; do doors
swing in or out? Why? [Fire Codes].
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Visibility
 Norman
(1988) recognized that our ability to
perceive and interpret these subtle clues is key to
our ability to operate a user interface.
– He defines a property of the user interface called
visibility to describe the how well the interface presents
these cues.
– To promote usability, the correct parts of the user
interface must be visible, and they must convey the
correct message.
– To be visible, a user interface must provide the
appropriate information for achieving relevant tasks.
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Examples of visibility


The holes in salt and pepper shakers help us identify which
shaker is which.
From Norman - I have a slide projector on which the slides
are changed with a single button, yet I sometimes want to
move the magazine backwards instead of forwards. To do
so requires me to hold the button down for a longer press.
This is invisible and makes for difficult use even when one
knows how to do it and horrendous learning at first. (note
many multifunction watches are similar)
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Too much visibility can be a
bad thing
 Norman
(1988) points out that if a user interface
has too many cues, the user may become confused
or overwhelmed

From Norman. In England, I visited a home with a fancy
new Italian washer-drier combination, with super-duper
multi-symbol controls, all to do everything you ever
wanted to do with the washing and drying of clothes. The
husband (an engineering psychologist) said he refused to
go near the thing. The wife (a doctor) said she had
memorized one setting and tried to ignore the rest.
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Norman’s Too Much Visibility
Example (cont.)

Someone went to a lot of trouble to create that design. I
read the instruction manual. That machine took into
account everything about today's wide variety of synthetic
and natural fabrics. The designers worked hard. They
really cared. But obviously they had never thought of
trying it out or of watching someone try to use it.
– If the design was so bad, if the controls were so
unusable, why did the couple purchase it? If people
keep buying poorly designed products, manufacturers
and designers will think they are doing the right thing
and continue as usual.
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An important property of
visibility
 Visibility
must be interpreted for the
specific context in which users will be
performing their tasks!
14
To summarize so far
 A user
interface provides information to the
user.
 Experience helps the user find these clues.I
 f the clues are absent or confusing, the
interface will likely be difficult to operate.
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The user’s role in the
process.
 The
user receives information from the
environment.
 This information, in concert with the user’s
prior knowledge allows them to build
mental models of the device, its
functionality and operation.
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User Models of Devices
 We
understand how things work come from
a mental (internal) model of the device or
interface.
– We build mental models of how to operate a
device based in part on what user interface tells
you about how a system functions (what it
does).
– Your mental model of the bicycle in from
Carelman tells you that the bike will not work.
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User Models of Devices
 Our
mental model is based in part on clues for
how things work, from the visible structure of the
device. In particular, we perceive
– What can you do with the interface (called
“Affordances” by Norman)
– How does the interface limit what you can do with it or
how its usage is constrained (called “Constraints” by
Norman)
– What is the relationship of action at the user interface to
action of the device (called “Mappings” by Norman)
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-- Information from a User
Interface - Consider scissors




What is the user interface - UI are the finger holes.
What can you do with the interface - UI affords (allows
you to) put fingers through holes and grasp scissors.
How is the use of the interface constrained - Use of UI is
constrained by size of holes in context of finger size.
What is the mapping between the operation of the interface
and the resulting function - Mapping is between holes and
blades. Move the holes in and out and the blades slice
together and apart.
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In-Class Exercise
 Consider
the everyday objects that your
teacher brought to class.
–
–
–
–
Identify interface
How do you operate the device?
How is the operation constrained?
How is the input of the interface related to the
expected function?
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More about Mappings and how they can
go wrong. Don Norman's Refrigerator
 Don
Norman's refrigerator has the controls
that are shown in 1.8. Suppose the freezer
is too cold but the fresh food is just right.
How would you adjust the controls so that
the freezer is warmer, and the fresh food
stays the same?
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Don Norman’s Refrigerator (2)
 There
are two possible models of the
refrigerator's operation because there are
two possible mappings of controls to
function. (fig 1.9)
 Which is right? Turns out that it is "B" and
that the controls are not independent, even
though they look as if they are.
22
Example - mappings. Don
Norman's stove. 3.3 - 3.5
-
How well/ natural controls map to
functions they control (including affordance
and constraints)
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Example mappings



Recall Mappings - relationships of interface to action.
Consider the relationship between a set of controls and the
results in a device.
For example, with a steering wheel, turning the wheel to
the right makes the tires turn right. The mapping is the
relationship between steering wheel interface and the
action of the tires.
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User Models Conclusions




A device which leads to a good user mental model is likely
to be more usable than one that does not lead to such a
model.
For everyday things, the user models are not necessarily
complex.
When our mental model is incorrect or inadequate, we may
have problems using the device.
The closer the mapping between the control (user
interface) and its function, the more accurate the user
model
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Feedback
 Definition
- sending back to the user
information about what action has actually
been done or what action has been
accomplished.
 Feedback is a mechanism by which users
can adjust their mental models.
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Feedback examples



Old style telephones provided tactile feedback ("feel"
when you pushed a button), sound feedback (tone sound
when you pushed a button), sounds from the connection.
Contemporary style phones have more functions but often
less feedback.
Contemporary phones may be more difficult to learn and
feel confident about using.
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Conclusions



Everyday devices have an interface. The user interface is
the boundary between the user and the function of the
device.
Information perceived from the user interface in concert
with the user’s knowledge are used to form a mental model
of the device and its operation.
Some specific information from the user interface that is
potentially incorporated into this mental model are how the
device is to be used, how its use is constrained and how the
operation of the interface maps to the functional outcome.
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More Conclusions
 Feedback
from the user interface is a way that
users can check and evolve their mental models.
 Everyday
devices can be designed well or poorly
for the user and the task. We cannot evaluate their
design independently of either the user’s
background or the context of the task.
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Overview of KEY issues for Chapter 1.

All objects have a user interface. The user interface is the boundary
between the person and the functionality of the device. If the boundary
is transparent or seamless, the UI is probably usable. If the boundary
is a barrier, it is probably not very usable.

Most people experience the functionality of the device as it is
presented in the UI. Designers must separate the functionality of the
device from the UI.

Here is an example of how functionality and UI are different. Quote
from CEO of DEC. He can't operate his microwave, but he probably
understands the physics of how the microwave works. The failure of
the device is not in the functionality, but in the UI. But, if people can't
operate the UI, they are not likely to get to the functionality.
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Overview of KEY issues for Chapter 1
 The UI is sort of like the "skin" of an object. The UI is where people
often get information as to how to operate an object.
 How do we get this information? We perceive information from the UI
and build a mental model of the characteristics of the UI. This mental
model may be more or less accurate. Norman discusses the idea of the
UI presenting subtle clues.
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Overview of KEY issues for Chapter 1
 Perceptual information from a UI can be more or less "visible" in
Norman's terms or more or less "perceivable" in a more general sense. If
information is not visible, it is not likely that we will be able to operate the
UI. Norman's example of the European Post Office doors is a good
example of a UI in which the subtle clues (where to push) was not visible
because the door and its hardware were all transparent. Our ability to
extract subtle cues may also be compromised if the visible information is
misleading (eg, the word "Salt" on the pepper shaker) or if there is so
much visible information that it is in conflict with what we think is the
intended function of the device. Norman's example of the Italian
washer/dryer is an example in which the UI seems more complex than the
intended function.
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Overview of KEY issues for Chapter 1
 So good visibility of vital cues is critical for us to know how to operate the
UI. What are the nature of the cues or type of information that can be
extracted from the UI. There are at least three types of information that
are relevant. 1) Information about what we can do or how we are to
interact with the UI. Norman calls these the affordances of the device.
Examples for simple devices with simple UI's often involve pushing,
pulling, grasping. 2) Information about how is our interaction
constrained. For simple UI's we may be constrained by motor skill
considerations. 3) Information about the mapping of the action at the UI
to the function of the device.
 If any of these types of information is missing, difficult to extract
(perceive), or confusing, the UI will likely fail or at least be unusable.
Norman's stove and refrigerators are examples in which the apparent
mapping of UI actions to functions may be wrong.
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Overview of KEY issues for Chapter 1
 Feedback from a UI can enhance usability and help users form more
complete mental models of the operation of the device.
 When designing the UI's for complex systems, such as software, it is
instructive to think about how we form mental models and operate UI's for
simple devices. Complex system UI's can also fail if the user cannot
extract reliable information about the UI (poor visibility), if the
information about how the user interacts is wrong, if information about the
UI's constraints, relative to the user is wrong, if information about the
relationship of UI actions to functionality is wrong, and/or if the UI does
not provide feedback.
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