Cognitive, Physical, Sensory, and Functional Affordances

Cognitive, Physical, Sensory, and Functional Affordances
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Cognitive, Physical, Sensory, and Functional Affordances
in Interaction Design
H. Rex Hartson
Department of Computer Science – 0106
Virginia Tech
Blacksburg, VA 24061
Phone: 540/231-4857
Fax: 540/231-6075
email: hartson @vt.edu
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Cognitive, Physical, Sensory, and Functional Affordances
in Interaction Design
H. Rex Hartson
Department of Computer Science – 0106
Virginia Tech
Blacksburg, VA 24061
540/231-4857, hartson @vt.edu
…they may indeed look, but not
perceive, and may indeed listen,
but not understand
Mark 4.12 (NRSV)
Abstract
In reaction to Norman’s [1999] essay on misuse of the term affordance in human-computer
interaction literature, this article is a concept paper affirming the importance of this powerful
concept, reinforcing Norman’s distinctions of terminology, and expanding on the usefulness
of the concepts in terms of their application to interaction design and evaluation. We define
and use four complementary types of affordance in the context of interaction design and
evaluation: cognitive affordance, physical affordance, sensory affordance, and functional
affordance. The terms cognitive affordance (Norman’s perceived affordance) and physical
affordance (Norman’s real affordance) refer to parallel and equally important usability
concepts for interaction design, to which sensory affordance plays a supporting role. We
argue that the concept of physical affordance carries a mandatory component of utility or
purposeful action (functional affordance). Finally, we provide guidelines to help designers
think about how these four kinds of affordance work together naturally in contextualized HCI
design or evaluation.
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1. Introduction
Reacting to his urge to speak up while lurking among CHI-Web discussants over- using and
misusing the term affordance, Don Norman was compelled to explain the concept of
affordance in his essay [1999], ‘Affordance, conventions, and design’. We 1 agree with most
of what Norman said, but feel there is more to be said about the concept of affordance,
especially to the end of making it a useful and applicable concept for usability designers and
practitioners. Since Norman encouraged it in his opening paragraph: ‘Hope it doesn’t stop
the discussion again’ [Norman, 1999], we decided to add to the discussion, affirming the
importance of this powerful concept, reinforcing Norman’s distinctions of terminology, and
adding some of our own ideas about applying affordance to interaction design and
evaluation.
1.1.
The importance of semantics and terminology
This is a concept paper, not a methodology paper or a report of an empirical study. The
epistemological cycle in the science of human-computer interaction (HCI), as in most
disciplines, alternates empirical observation with theory formulation to explain and predict
the observed. Norman’s stages of action model [1986] is a practical example of HCI theory,
in that it explains and predicts what users do while interacting with systems (from
refrigerators to computers) to accomplish goals in a work domain. It is our intention here to
develop more fully some key concepts as a contribution to that kind of HCI theory.
In essence this paper is about semantics and terminology to express semantics. HCI is a
relatively young field and the terminology we require for discussing, analyzing, and applying
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Although this is a single-author paper, most of it is written in first person plural to acknowledge much help from many
HCI colleagues at Virginia Tech.
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our concepts with a common understanding is incomplete. The terms we use for concepts are
not inherently important, but the semantics behind the terminology commands our attention.
In response to, ‘It’s just semantics,’ we heartily agree with Allen and Buie [2002, p. 21] who
proclaim: ‘Let us say it outright: There is no such thing as just semantics. . . . In
communication, nothing is more important than semantics.’ Allen and Buie [2002, p. 18] are
dead on: ‘This isn’t just nit-picking—a rich and evocative word like intuitive is wasted as
long as it sits in a fog of uncertain associations.’ This statement was never more true than it
is for the term affordance, as Norman’s essay [1999] attests. Shared meanings and
representations (through common language) are an absolute must in science, art, and
everything in-between.
1.2.
Gibson on affordance
Norman begins by referring to Gibson’s earlier definitions of afford and affordance [1977;
1979], as well as to discussions he and Gibson have had about these concepts. Setting a
paraphrase of Gibson [1979, p. 127] within an HCI design context, affordance as an attribute
of an interaction design feature is what that feature offers the user, what it provides or
furnishes. Here Gibson is talking about physical properties, what Norman calls real
affordances. Gibson gives an example of how a horizontal, flat, and rigid surface affords
support for an animal. In his ecological view, affordance is reckoned with respect to the
user, in this case the animal, who is part of the affordance relationship. Thus, as Norman
[1999] points out, Gibson sees an affordance as a physical relationship between an actor
(e.g., user) and physical artefacts in the world reflecting possible actions on those artefacts.
Such an affordance does not have to be visible, known, or even desirable.
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1.3.
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Norman on affordance
In his article, Norman [1999] takes issue with a common and growing misuse (or perhaps
uninformed use) of the term affordance. In simple terms, much of the difficulty stems from
confusion between what Norman calls real affordance and perceived affordance. To Norman
[1999], the unqualified term affordance refers to real affordance, which is about physical
characteristics of a device or interface that allow its operation, as described by Gibson in the
previous section. However, in many HCI and usability discussions the term is also used
without qualification to refer to what Norman calls perceived affordance, which is about
characteristics in the appearance of a device that give clues for its proper operation. Since
the two concepts are very different, perhaps orthogonal, Norman admonishes his readers not
to misuse the terms and, in particular, not to use the term affordance alone to refer to his
concept of perceived affordance and, perhaps, not to use these terms at all without
understanding the difference.
1.4.
Seeking a balance for interaction designers
In these admonishments [1999], Norman focuses mainly on real affordance. We believe that
what Norman calls perceived affordance has an equally important role, perhaps even a
starring role, in interaction design. We know that Norman believes this, too. In his book
Design of Everyday Things [Norman, 1990], sometimes called the DOET book – formerly
Psychology of Everyday Things [Norman, 1988], known as the POET book – Norman
describes his struggles with refrigerators, British water taps, and other physical devices and
says much about perceived affordances in the context of problems that users of these devices
have in determining how to operate them. Norman feels that DOET might have played a part
in the confusion of terms because, as he says [1999], ‘I was really talking about perceived
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affordances, which are not at all the same as real ones’. However, in the course of
emphasizing the difference in his more recent article, we feel that the importance of
perceived affordances became somewhat lost, leaving researchers and practitioners in a
quandary about how we can legitimately refer to this important usability concept. In hopes
of a remedy we offer a perspective on the concept of affordance that has been working for us.
We would like to strike a balance and we think Norman would approve.
1.5.
Objectives
We think it is healthy when an article like Norman’s leads to a follow-up discussion,
especially about a topic essential to interaction design. In that spirit, this is not a critique or
rebuttal. Rather, Norman has called for understanding of these concepts, and has highlighted
the problem of inadequate terminology. We wish to respond to that call by suggesting
terminology for four kinds of affordance without violating Norman’s or Gibson’s basic
precepts but, in fact, amplifying and extending them in a useful way. Like Norman, we
would like to see these concepts understood and properly distinguished in their use by
researchers and practitioners alike. In the process, we would also like to give Norman credit
for a broader contribution in his stages-of-action model [Norman, 1986] than perhaps he may
have given himself.
We have named the different kinds of affordances for the role they play in supporting users
during interaction, reflecting user processes and the kinds of actions users make in task
performance. Norman’s perceived affordance becomes cognitive affordance, helping users
with their cognitive actions. Norman’s real affordance becomes physical affordance, helping
users with their physical actions. We add a third kind of affordance that also plays an
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important role in interaction design and evaluation, sensory affordance, helping users with
their sensory actions. A fourth kind, functional affordance, ties usage to usefulness. We
offer guidelines for considering these kinds of affordance together in a design context.
2. Related work
2.1.
Calibrating terminology
Since Norman brought the term affordance into common usage in the HCI domain with his
book Design of Everyday Things [Norman, 1990], the term has appeared many times in the
literature. For example, an interesting recent treatment by Thimbleby shows how key aspects
can be formalised as mathematical symmetry [2002].
In this section, we show the relationships among others’ use of the terminology and ours. In
so doing, we give a preview of our definitions and usage, along with a rationale for our
particular choices.
Beyond Gibson and Norman, McGrenere & Ho [2000] and Gaver [1991] have influenced our
thinking about affordances. McGrenere & Ho [2000] give credit to Gibson for originating
the concept of affordance in psychology and to Norman for introducing this important
concept into human-computer interaction. McGrenere & Ho also target current misuse and
confusion of terms, noting the need to clarify the concepts for effective communication
among researchers and practitioners and make a connection to usability design. Gaver
[1991] sees affordances in design as a way of focusing on strengths and weaknesses of
technologies with respect to the possibilities they offer to people who use the m. Gaver also
summarizes his view of the Gibson and Norman contributions. He extends the concepts by
showing how complex actions can be described in terms of groups of affordances, sequential
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in time and/or nested in space, showing how affordances can be revealed over time, with
successive user actions, for example, in the multiple actions of a hierarchical drop-down
menu. That McGrenere and Ho [2000] also needed to calibrate their terminology against
Gaver’s further demonstrates the difficulty of discussing these concepts without access to a
richer, more consistent vocabulary. Table 1 shows how various authors use the terminology,
compared to usage in this paper.
Table 1. Comparison of affordance terminology
Hartson
Gibson
Norman
McGrenere & Ho
Gaver
Physical
affordance
Affordance
Cognitive
affordance
Perceptual
information about an
affordance
Real affordance Perceived affordance
Affordance
Perceptual
information about an
affordance
Affordance, also Perceptual
perceptible
information about an
affordance
affordance, also
apparent affordance
Sensory
affordance
Implied
Implied
Indirectly included
in perceptibility of
an affordance
Indirectly included
in perceptibility of
an affordance
In most of the related literature, design of cognitive affordance (whatever it is called in a
given paper) is acknowledged to be about design for the cognitive part of usability, ease-ofuse in the form of learnability for new and intermittent users (who need the most help in
knowing how to do something). But the concept gets confused because a cognitive
affordance is variously called a perceived affordance, an apparent affordance, or perceptual
information about an affordance.
What McGrenere & Ho and Gaver simply call an affordance and what Norman calls a real
affordance is, by and large, what we call a physical affordance, offered by artefacts that can
be acted upon or physically manipulated for a particular purpose. All authors who write
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about affordances give their own definitions of the concept, but almost no one, including
Norman [1986] (who, to be fair, intended to focus on the cognitive side) and McGrenere &
Ho [2000] (e.g., in their Section 6.2), mentions design of physical affordances. Design of
physical affordances is about design fo r the physical action part of usability, ease-of- use in
the form of high performance and productivity for experienced and power users as well as to
help disabled users achieve maximum efficiency in physical actions. McGrenere & Ho come
close to recognizing this role of physical affordance in design in the discussion about their
Figure 4, which relates cognitive affordance and physical affordance to design improvement.
Most other authors, including those in Table 1, include sensory affordance only implicitly
and/or lumped in with cognitive affordance rather than featuring it as an separate explicit
concept. Thus, when these authors talk about perceiving affordances, including Gaver’s and
McGrenere & Ho’s phrase ‘perceptibility of an affordance’, they are referring (in our terms)
to a combination of sensing (e.g., seeing) and understanding physical affordances through
sensory affordances and cognitive affordances. Gaver refers to this same mix of affordances
when he says, ‘People perceive the environment directly in terms of its potential for action’.
As we explain in the next section, our use of the term ‘sense’ has a markedly narrower
orientation on sensory inputs such as seeing and hearing.
2.2. Level setting
Why maintain separate terms and concepts when they are to be integrated in design, anyway?
The answer is simply that the differences among these concepts requires that each type of
affordance must be identified for what it is and considered on its own terms in analysis and
design. Each type of affordance plays a different role, uses different mechanisms,
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corresponds to different kinds of user actions, exhibits different characteristics, has different
requirements for design, and implies different things in evaluation and diagnosis.
In this section we articulate a rationale for boundaries in the particular use of psychological
terminology in the context of affordances, guided by a motivation to clearly bring out issues
of HCI design and analysis. The concepts of sensing, perception, and cognition all have a
large scope in their broadest interpretation, too broad for isolating the HCI design factors of
affordances. In the general context of psychology, these concepts are more intertwined than
orthogonal. To avoid this intertwining we use, for example, the term ‘sensing’ instead of
‘perception’ in most places, because perception usually embraces significant cognition
[Hochberg, 1964]. Our motivation for attempting a degree of arbitrary
compartmentalization, via reasonable operational definitions that work on a practical level
for design, is that the HCI design issues we wish to associate with these levels of user actions
are mostly orthogonal.
While overlapping and borderline cases are interesting to psychologists, HCI designers want
to avoid marginal design and ensure that designs work for wide-ranging user characteristics.
An abstraction that separates the types of user actions (e.g., sensing from cognition) removes
the overlap. As an illustration, consider text legibility, which at a low level is about
identifying shapes in displayed text as letters in the alphabet, but not about the meanings of
these letters as grouped into words and sentences. Text legibility is an area where user
perception, sensing, and cognition can overlap. To make out text that is just barely or almost
barely discernable, users can augment or mediate sensing with cognition, using inference and
the context of words in a message to fill in the blanks. Context can make some candidate
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letters more likely than other. Users can recognize words in their own language more easily
than words in another language or in nonsense letter combinations.
In contrast, HCI design in this context requires solutions resolved on the side of pure sensing.
Simply put, a label in a user interface that cannot be fully discerned by the relevant user
population, without reliance on cognitive augmentation, is a failed HCI design. Thus, we
wish to define sensing at a level of abstraction that eliminates these cases of borderline user
performance so that HCI designers can achieve legibility, for example, beyond question for
the target user community. We desire an understanding of affordance that will guide the HCI
designer to attack a text legibility problem by adjusting the font size, for example, not by
adjusting the wording to make it easier to deduce text displayed in a tiny font.
In our abstraction, a user’s sensory experience can include gestalt aspects of object
appearance and perceptual organisation [Arnheim, 1954; Koffka, 1935], such as
figure/ground relationships, and might sometimes include some judgment and lexical and
syntactic interpretation in the broadest spatial or auditory sense (e.g., what is this thing I am
seeing?), but does not get into semantic interpretation (e.g., what does it mean?). In the
context of signal processing and communications theory, this kind of sensing would be about
whether messages are received correctly, but not about whether they are understood.
A discussion of HCI design without the kind of abstraction we propose can degenerate to hair
splitting about levels of human information processing that distract from the practical design
issues, further putting off practitioners who may already believe that concepts like affordance
are just fodder for academic exercises.
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3. Our proposal
To pursue the objectives of Section 1.5, specifically in the context of interaction design and
evaluation for computer-based systems, we propose (the essence of the va lue-added in this
article):
1. to clarify and define the terms cognitive affordance and physical affordance to refer
to parallel and equally important usability concepts for interaction design,
2. that the concept of physical affordance carries a mandatory component of utility or
purpose, which we call functional affordance, and that statements about physical
affordance must include a reference to that purpose,
3. to add the concept of sensory affordance, supporting cognitive affordance and
physical affordance in design, and
4. that cognitive, physical, sensory, and functional affordance be connected and
considered together in any HCI design or evaluation context.
3.1.
Cognitive and physical affordance – an alliance in design
The relevant part of what my dictionary says about ‘to afford’ is that it means to yield, to
give, or to furnish. In design, an affordance gives or provides something that helps a user do
something. For example, the study window in my house affords me a fine view of the forest;
the window helps me see that nice view. Norman’s stages-of-action model [1986] describes
the typical course of interaction between a human user and a computer or any kind of
machine. During interaction, a user performs cognitive, physical, and sensory actions and
requires affordances to help with each. In our work on the User Action Framework [Andre,
Hartson, Belz, & McCreary, 2001; Andre, Belz, McCreary, & Hartson, 2000; Hartson,
Andre, Williges, & van Rens, 1999], based on Norman’s model, we have also found a need
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for all four kinds of affordance in the context of interaction design and usability. It is in that
context that we offer these definitions.
A cognitive affordance is a design feature that helps, aids, supports, facilitates, or enables
thinking and/or knowing about something. As a simple example, clear and precise words in
a button label could be a cognitive affordance enabling users to understand the meaning of
the button in terms of the functionality behind the button and the consequences of clicking on
it. A physical affordance is a design feature that helps, aids, supports, facilitates, or enables
physically doing something. Adequate size and easy-to-access location could be physical
affordance features of an interface button design enabling users to click easily on the button.
Since physical affordance occurs with physical objects, I am treating active interface objects
on the screen, for example, as real physical objects, since they can be on the receiving end of
real physical actions by users. As many in the literature have pointed out, it is clear that a
button on a screen cannot be pressed. Restricting the discussion to clicking on buttons easily
dispatches this difficulty.
Norman [1999, p. 41] says that symbols and constraints are not affordances and that wording
in the label on a button, for example, is symbolic communication. We agree, but under our
definition, communication is exactly what makes good wording effective as a cognitive
affordance: something to help the user in knowing (e.g., knowing what to click on). We see
symbols, constraints, and conventions as essential underlying mechanisms that make
cognitive affordances work, as Norman says, as ‘powerful tools for the designer’. As
Norman further says, the only way we know for sure if users share designers’ perceptions of
these symbols and conventions is by usability data. Thus, and we think this is a point that
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Norman particularly had in mind in his article, if a designer claims to have ‘added an
affordance’ to the interaction design, that in itself says nothing about usability.
In the DOET [Norman, 1990] tradition, we illustrate with a simple and ubiquitous noncomputer device, a device for opening doors. The hardware store carries both round
doorknobs and lever type door handles. The visual design of both kinds conveys a cognitive
affordance helping users think or know about usage through the implied message their
appearance gives to users: ‘This is what you use to open the door’. The doorknob and lever
handle each suggests, in its own way, the grasping and rotating required for operation.
Again, we agree with Norman in noting that the message implied is based on convention and
there is nothing intrinsic in the appearance of a doorknob that necessarily conveys this
information. On another planet, it could seem mysterious and confusing, but for us a
doorknob is an excellent cognitive affordance because almost all users do share the same
easily recognized cultural convention.
Door operation devices also provide physical affordance, to help users do the opening and
closing – some better than others. For example, many users prefer the lever type to a round
knob because the lever is easier to use with slippery hands or by an elbow when the hands are
full. The push bar on double doors in another example of a physical affordance helpful to
door users with full hands.
Sometimes the physical affordance to help a user open a door is provided by the door itself;
people can open some swinging doors by just pushing on the door. In such cases designers
often help users by installing, for example, a brass plate to show that one should push and
where to push. Even though this plate might help avoid handprints on the door, it is a
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cognitive affordance and not a real physical affordance, because it adds nothing to the door
itself to help the user in the physical part of the pushing action. Sometimes the word ‘Push’
is engraved in the plate to augment the clarity of meaning of the plate as a cognitive
affordance.
Similarly, sometimes the user of a swinging door must open it by pulling. The door itself
does not usually offer sufficient physical affordance for the pulling action, so a pull handle is
added. A pull handle offers both cognitive and physical affordance, providing a physical
means for pulling as well as a visual indication that pulling is required.
Norman discusses many such everyday devices in his DOET book [1990] and makes it clear
that, when he speaks of knowing how to operate a device, he is referring to cognitive
(perceived, in his terminology) affordance, characterizing a view of cognitive affordance that
we share [Norman, 1999, p. 39]: ‘When you first see something you have never seen before,
how do you know what to do? The answer, I decided, was that the required information was
in the world: the appearance of the device could provide the critical clues required for its
proper operation’. However, when Norman later says that affordances play a relatively
minor role in the world of screen-based systems [1999, p.39], he clearly is talking about
physical affordances (and the statement is true only if one is not concerned with design
factors for physical actions, such as those involving Fitts’ law [MacKenzie, 1992], physical
disabilities, or the physical characteristics of interaction devices). And we think Norman
would agree that cognitive affordances play an enormously important role in interaction
design; cognitive affordances are one of the most significant user-centred design features in
present-day interactive systems, screen-based or otherwise. They are the key to answering
Norman’s question: ‘How do you know what to do?’ And, yes, the design of cognitive
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affordances can depend greatly on cultural conventions as a common base for
communicating the meaning of visual cues from designer to user.
Continuing in the DOET tradition of non-computer examples, we have known many different
kinds of wine bottle openers, possessing a range of effectiveness. Although most people
understand how to use the kinds of openers shown in Figure 1, their design could offer better
physical affordance, to help the user in doing the physical task for which they were intended.
Because of somewhat crude mechanical operation, they often manage to crumble the cork,
leaving bits unappetizingly bobbing in the newly liberated libation.
Figure 1. Ordinary cork pullers with acceptable cognitive affordance
In contrast a colleague, Roger Ehrich, recently gave me the marvelously efficient and reliably
effective cork puller shown in Figure 2.
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Figure 2. A cork puller with good physical affordance but non-obvious cognitive affordance
The problem with this device, though, is that its proper use was initially anything but obvious
to me. For the sake of science, we have been increasing the frequency of informal user-based
tests and find that an average of more than nine out of ten wine-drinking guests who have not
seen this design before cannot determine how to use it in a reasonably short time. This
device offers excellent physical affordance to help in doing the task, making it a good design
for an experienced user such as a wine steward. However, it does not offer good cognitive
affordance for helping intermittent and first-time users know or learn how to use it.
The secret to operation lies in shifting between modes in a classic case of moded design:
there are two states, and in each state user actions and inputs have meanings and outcomes
that are different from those of the other state (see Chapter 11 of Thimbleby [1990]). The
thick piece of metal connecting the T- handle to the threaded shaft, at the left of Figure 2, is
what makes this opener different from most others. By swiveling, it functions as a kind of
‘gear shift’ that changes the way the threads are engaged, lending the modality to the design.
Figure 3 shows the T- handle moved to the top of the threaded shaft and the shifting
mechanism in the centre has locked the T- handle to a fixed position on the threaded shaft.
When the T-handle is rotated in this cork engagement mode, the threaded shaft turns and the
corkscrew at the bottom dives deftly into the cork.
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Figure 3. T-handle locked to threaded shaft in the cork engagement mode
Then the shifting mechanism is swiveled, unlocking the T- handle from the shaft, putting the
device in lifting mode. When the T- handle is now turned (in the same direction as before),
the shaft does not turn but the T-handle moves along the threads on the shaft, lifting the cork,
as in Figure 4.
Figure 4. T-handle moving on the shaft threads in lifting mode
3.2.
Functional affordance – design for purposeful action
The second part of our proposal is to bring Gibson’s ecolo gical view into contextualized HCI
design by including a purpose in the definition of each physical affordance. Putting the user
and purpose of the affordance into the picture harmonizes nicely with our interaction- and
user-oriented view in which an affordance helps or aids the user in doing something.
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As Norman points out [1999, p. 40], his own definition of (physical) affordance means that
all interface designs afford clicking anywhere on the screen, whether a button is there or not,
except where the pointer is constrained from being in certain parts of the screen (a
hypothetical condition that Norman introduced to make his point). But that kind of clicking
is without reference to a purpose and without the requirement that any useful reaction by the
system will come of it. But, of course, we need more than that in a task-oriented context of
interaction design, where user actions are goal-oriented and purposeful. A user doesn’t click
on the screen just because it’s possible. A user clicks to accomplish a goal, to achieve a
purpose (e.g. clicking on a user interface object, or artefact, to select it for manipulation or
clicking on a button labeled ‘Sort’ to invoke a sorting operation). So, if designers or users
say this button affords clicking, we would understand this to mean the button is sensitive to
clicking in the sense that the system will usefully respond to clicking. But even this
interpretation does not go far enough to meet our proposed requirement to associate purpose
with physical affordance. It is more useful to be specific about the purposeful response and
say that the button affords clicking to initiate, for example, the Sort function. A blank space
on the screen next to the but ton, or another button elsewhere on the screen, does not provide
that same kind of physical affordance. Adding the purpose for a physical affordance adds
sense and a goal orientation to a design discussion.
The study window in my house affords me a fine view of the forest, but I have to participate
by looking through the window to accrue the benefit of seeing that view. Gibson implicitly
included reference to purposeful enablement: a horizontal, flat, rigid surface affords an
animal to stand, walk, or run. Gibson is indeed talking here about purposeful activity, as he
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is in the discussion [1979], for example, about how objects (artefacts) afford manipulation
(e.g. a pole that can be used by a chimpanzee as a rake to reach a banana).
In Norman’s DOET world of non-computer devices, a purpose for a physical affordance is
always implied. The doorknob is a cognitive and physical affordance for operating the door.
The physical affordance offered by a doorknob does not mean merely that the doorknob can
be grasped and turned. It means that the doorknob can be grasped and turned in order to
operate (e.g. invoke the function or mechanism of opening) the door; the user is enabled to
operate the door. In turn, the door itself is a functional affordance that, when invoked, allows
passage. In this interaction design view, a physical affordance gives access to functionality,
the purpose of the physical affordance used to access it.
McGrenere & Ho [2000] also refer to the concept of application functionality usefulness,
something they call ‘affordances in software’. In an external view it is easy to see a system
function as an affordance because it helps the user do something in the work domain. This
again demonstrates the need for a richer vocabulary, and conceptual framework, to take the
discussion of affordances beyond user interfaces to the larger context of overall system
design. We use the term functional affordance to denote this kind of higher- level user
enablement in the work domain.
As McGrenere & Ho [2000] point out, requiring purposeful action as a component of
physical affordance nicely substantiates the dual concepts of usability and usefulness
[Landauer, 1995]. Usefulness stems from the utility of functional outcomes of user actions.
In contrast, usability stems from the effectiveness of cognitive affordances for understanding
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how to use physical affordances, from the physical ease of using the physical affordances,
and from the sensing of these via sensory affordances.
In sum, the addition of purpose to the description of a physical affordance is an obvious
extension, but it should be made explicit, to avoid the ambiguities Norman has described.
This extension to the concept of physical affordance might possibly go beyond what either
Gibson or Norman had in mind, but we think it makes sense and is not difficult to justify in
the domain of design.
3.3.
Sensory affordance – a supporting role
The third part of our proposal is to include the concept of sensory affordance. A sensory
affordance is a design feature that helps, aids, supports, facilitates, or enables the user in
sensing (e.g., seeing, hearing, feeling) something. Sensory affordance includes design
features or devices associated with visual, auditory, haptic/tactile, or other sensations.
Cognitive affordance and physical affordance are stars of interaction design but sensory
affordance plays a critical supporting role. In short, sensory affordance can be thought of as
an attribute of cognitive affordance or physical affordance; users must be able to sense
cognitive affordances and physical affordances in order for them to aid the user’s cognitive
and physical actions. Sensing cognitive affordances is essential for their understanding, and
sensing physical affordances is essential for acting upon them. Sensory affordance issues of
user interface artefacts include noticeability, discernability, legibility (in the case of text), and
audibility (in the case of sound). In the concept of sensory affordance, as we explained in
Section 2.2, we have deliberately included only the physical act of sensing and not any of the
cognitive aspects that are often associated with the term perception.
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3.4.
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Contextualized design as nexus of affordance roles
The fourth part of our proposal is to connect all four kinds of affordance in a design context.
To put Gibson’s ecological view in HCI terms, affordances have a relational ontology: their
existence as an affordance is relative to the environment of users and usage. In HCI, the
user’s environment is the work context plus the interaction design. To accomplish work
goals, the user must sense, understand, and use affordances within an interaction design.
Gaver [1991] says that affordances are a powerful approach for thinking about technology
because the effectiveness of an affordance depends on the attributes of both the artefact and
the user. The concept of affordance is an instrument for focusing on links in design among
the user, the actions, and the artefacts. The user’s path from sensing to cognition to action
shows how each affordance role is involved in both learning about (ease of learning) and
using (ease of use) artefacts. The idea is to include both user and artefact attributes in
affordance designs as part of the complementarity that Gaver describes, between actor and
acted-upon environment. Gaver’s ecological perspective offers a succinct approach to
artefact design through an immediate connection between cognitive and physical
affordances.
In Gestalt psychology [Koffka, 1935], well before Gibson or Norman, we see the connection
of cognitive affordance to physical affordance and its purpose [Gibson, 1979, p. 138]. The
meaning or value or use of a thing can be seen and understood through that object (at least if
an effective design or cultural convention supports it), just as one can see its size or colour.
Similarly, we design human-computer interaction for the user to understand the operation
and purpose of a physical affordance through sensing (via sensory affordances) and
understanding associated cognitive affordances.
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Norman [1999, p. 41] says, ‘Affordances (meaning physical affordances) specify the range
of possible activities, but affordances are of little use if they aren’t visible to the users’,
meaning ‘visible’ in both the sensory (detectable or observable) and cognitive sense
(understandable). Physical affordance is associated with the ‘operability’ characteristics of
user interface artefacts. Cognitive affordance is associated with semantics or meaning of
user interface artefacts. Sensory affordance is associated with the ‘sense-ability’
characteristics of user interface artefacts, especially of physical affordances and cognitive
affordances. In the domain of human-computer interaction, as in the domain of everyday
physical devices, design is what connects physical affordances to the cognitive affordances
that ‘advertise’ them and explain how to use, when to use, and whether to use each physical
affordance. Design is also what connects sensory affordances to cognitive and physical
affordances, so they can be seen or heard or felt (and eventually tasted or smelled) to be used.
Table 1 contains a summary of these affordance types and their roles in interaction design.
Table 1. Summary of affordance types
Affordance Type
Description
Cognitive affordance
Design feature that helps
users in knowing something
Physical affordance
Sensory affordance
Functional affordance
Design feature that helps
users in doing a physical
action in the interface
Design feature that helps
users sense something
(especially cognitive
affordances and physical
affordances)
Design feature that helps
users accomplish work (i.e.,
the usefulness of a system
function)
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Example
A button label that helps
users know what will happen
if they click on it
A button that is large enough
so that users can click on it
accurately
A label font size large
enough to read easily
The internal system ability to
sort a series of numbers
(invoked by users clicking on
the Sort button)
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3.4.1
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A positive association of affordance roles as structured HCI design guidance
A design methodology based solely on affordance concepts cannot substitute for an effective
design methodology set in a complete development life cycle [Hix & Hartson, 1993;
Mayhew, 1999; Rosson & Carroll, 2002]. However, we do offer some guidelines to urge
designers to think about how these four kinds of affordance work together naturally in the
design of a user interface (or other) artefact.
McGrenere & Ho (Section 6.4 of [2000]) also allude to the possibility of affordances as a
framework for design. But they, too, fall short of prescribing a design methodology based on
affordances. It is plausible to codify and integrate affordance concepts so that they can be
brought to bear systematically in interaction design, but the resulting approach would have to
be evaluated in a summative study before one could make claims about the efficacy of this
approach as a ‘method’. Nonetheless, it is incumbent on HCI theory to find useful
application to HCI design and analysis.
In the case of affordances, the theory offers a way to tie the different kinds of affordance to
the HCI (or any human- machine interaction) design process in an organised way. HCI
design must address (at least) two components, tasks and artefacts [Carroll, Kellogg, &
Rosson, 1991]. For developing the work flow of an application, task analysis is useful to
inventory the tasks, and usage scenarios [Rosson & Carroll, 2002] are necessary to guide
design. Affordance theory can guide design of HCI artefacts. Each kind of affordance plays
a different role in the design of different attributes of the same artefact, including design of
appearance, content, and manipulation characteristics to match users’ needs, respectively, in
the sensory, cognitive, and physical actions they make as they progress through the cycle of
actions during task performance. As Gaver [1991, p.81] says, thinking of affordances in
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terms of design roles ‘allows us to consider affordances as properties that can be designed
and analysed in their own terms.’ Additionally, even though the four affordance roles must
be considered together in an integrated view of artefact design, these words from Gaver
speak to the need to distinguish individually identifiable affordance roles.
As an example of how the concepts might guide designers, suppose the need arises in an
interaction design for a button to give the user access to a certain application feature or
functionality. The designer would do well to begin by asking if the intended functionality,
the functional affordance, is appropriate and useful to the user. Further interaction design
questions are moot until this is resolved positively.
The designer is then guided to support cognitive affordance in the button design, to advertise
the purpose of the button by ensuring, for example, that its meaning (in terms of a taskoriented view of its underlying functionality) is clearly, unambiguously, and completely
expressed in the label wording, to help the user know when it is appropriate to click on the
button while performing a task. Then, the designer is asked to consider sensory affordance in
support of cognitive affordance in the button design, requiring an appropriate label font size
and colour contrast, for example, to help the user discern the label text to read it.
The designer is next led to consider how physical affordance is to be supported in the button
design. For example, the designer should ensure that the button is large enough to click on it
easily to accomplish a step in a task. Designers should try to locate the button near other
artefacts used in the same and related tasks, to minimize mouse movement between task
actions. Finally, the designer is guided to consider sensory affordance in support of physical
affordance in the button design by ensuring that the user notices the button, so it can be
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clicked. For example, the button must be a colour, size, and shape that make it noticeable
and must be located in the screen layout so that it is near enough to the user’s focus of
attention. If the artefact is a feedback message, it also requires attention to sensory
affordance (e.g., to notice the feedback), cognitive affordance (e.g., to understand what the
message says about a system outcome), and physical affordance (e.g., to click on a button to
dismiss the message box).
In sum, the concept of affordance does not offer a complete prescriptive approach to
interaction design but does suggest the value of considering all four affordance roles together
in design of an interaction artefact by asking (not necessarily always in this order):
1. Is the functionality to which this interaction or artefact gives access useful in
achieving user goals through task performance (functional affordance, or purpose of
physical affordance)?
2. Does the design include clear, understandable cues about how to use the artefact
(cognitive affordance), or about system outcomes if the artefact is a feedback
message?
3. Can users easily sense the visual (or other) cues about artefact operation (sensory
affordance in support of cognitive affordance)?
4. Is the artefact easy to manipulate by all users in the target user classes (physical
affordance)?
5. Can users easily sense the artefact for manipulation (sensory affordance in support of
physical affordance)?
Considering one affordance role but ignoring another is likely to result in a flawed design.
For example, if the wording for a feedback message is carefully crafted to be clear, complete,
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and helpful (good cognitive affordance), but users do not notice the message because it is
displayed out of the users’ focus of attention (poor sensory affordance) or users cannot read it
because the font is too small, the net design is ineffective. A powerful drag and drop
mechanism may offer a good physical affordance for opening files, but lack of a sufficient
cognitive affordance to show how it works could mean that most users won’t use it.
An example of a way that cognitive affordance and physical affordance work together in
interaction design can also be seen in the context of designing constraints for error
avoidance. ‘Graying out’ menu items or button labels to show that inappropriate choices are
unavailable at a given point within a task is a simple, but effective, error avoidance design
technique. This kind of cognitive affordance presents to the user a logical constraint,
showing visually that this choice can be eliminated from possibilities being considered at this
point. In that sense, the grayed-out label is a cognitive affordance on its own, quite different
from the cognitive affordance offered by the label when it is not grayed out.
If cognitive and physical affordances are connected in the design, a grayed-out button or
menu choice also indicates a physical constraint in that the physical affordance usually
offered by the menu item or button to access corresponding functionality is disabled so that a
persistent user who clicks on the grayed-out choice anyway cannot cause harm. Because
these two aspects of graying-out work together so well, many people think of them as a
single concept, but the connection of these dual aspects is evident to the user interface
programmer, who usually must make separate commands or declarations for the cognitive
and the physical parts – to gray out the displayed label appearance and to disable the artefact
behaviour so it will not respond to a click.
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3.4.2
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False cognitive affordances misinform and mislead
Because of the power of cognitive affordances to influence users, designers must be aware of
their responsibility to use them with caution. When cognitive affordances don’t telegraph
physical affordances or, worse, when cognitive affordances falsely telegraph physical
affordances, users encounter errors. Gibson calls this ‘misinformation in affordances’; for
example, as conveyed by a glass door that appears to be an opening but doesn’t afford
passage. Draper and Barton [1993] call these ‘affordance bugs’.
Sometimes a door has both a push plate and a pull handle as cognitive affordances in its
design. The user sees this combination of cognitive affordances as an indication that either
pushing or pulling can operate this as a swinging door. When the door is installed or
constrained so that it can swing in only one direction, however, the push plate and pull
handle introduce misinformation in the cognitive affordances that interfere with the design as
a connection to physical affordances. We know of a door with a push plate and a pull handle
that was installed or latched so that it could only be pushed. A ‘Push’ sign had been added,
perhaps to counter the false cognitive affordance of the pull handle. The label, however, was
not always enough to overcome the power of the pull handle as a cognitive affordance; we
observed some people still grab the handle and attempt to pull the door open.
Another example of a false cognitive affordance showed up in a letter recently received from
an insurance company. There was a form at the bottom to fill out and return, with this line
appearing just above the form:
- - - - - - - - - - - - - - - - - - - - - - Do not detach - - - - - - - - - - - - - - - - - - - - - -
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Because that dashed line looked so much like the usual ‘Cut on this line to detach’ cognitive
affordance, I almost did detach the form before realizing that the information above,
identifying me as a customer, would be lost if I did.
Examples of false cognitive affordances in user interfaces abound. A common example is
seen in Web page links that look like buttons, but don’t behave like buttons. The gray
background to the links in the top menu bar of a digital library Web site, Figure 5, makes
them seem like buttons. A user might click on the background, assuming it is a button, and
not get any result. Because the ‘but ton’ is actually just a hyperlink, it requires clicking
exactly on the text.
Figure 5. False cognitive affordances in a menu bar with links that look like buttons
Below-the-fold issues on Web pages can be compounded by having a horizontal line on a
page that happens to fall at the bottom of a screen. Users see the line (as a false cognitive
affordance) and assume that it is the bottom of the page, and so do not scroll, missing
possibly vital information below.
Sometimes a false cognitive affordance arises from deliberate abuse of a shared convention
to deceive the user. Some designers of pop-up advertisements ‘booby trap’ the ‘X’ box in
the upper right hand corner of the pop-up window, making it a link to launch one or more
new pop-ups when users click on the ‘X’, trapping users into seeing more pop-up ads when
their intention clearly was to close the window.
McGrenere & Ho [2000] make a point that the case in their Figure 2 labeled ‘false
affordances’ is problematic because ‘it is not the affordance that is false; rather, it is the
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information that is false’ [McGrenere & Ho, 2000, p. 5]. Affordance roles can help clarify
this kind of discussion by allowing us to say that a cognitive affordance (the information
McGrenere and Ho refer to) can be considered false when it indicates something about a
physical affordance that doesn’t exist or indicates something incorrect about a physical
affordance that does exist.
As another example, I have a radio with a slider switch for selecting between stereo and
monaural FM reception, sketched in Figure 6a. The names for the switch positions (Stereo,
Mono) are a good match to the user’s model, but the arrows showing which way to slide the
switch are unnecessary and introduce confusion when combined with the labels.
FM
FM
Stereo
Mono
Mono
Stereo
Figure 6. Radio switch with mixed affordances
a. existing design
b. better design
The design has mixed cognitive affordances: the names of the modes at the top and bottom of
the switch are such a strong cognitive affordance for the user that they conflict with the
arrows. The arrows in Figure 6a call for moving the switch up to get monaural reception and
down to get stereo. At first glance, however, it looks as though the up position is for stereo
(toward the ‘stereo’ label) and down is for monaural, but the arrows make the meaning
exactly the opposite. The names alone, as shown in Figure 6b, are the more normal and
natural way to label the switch.
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4. The user’s role in evaluation and redesign – a trail of user-made artefacts
It is not uncommon to see modifications to designs made by users: trails of user-created
artefacts blazed in the wake of spontaneous formative evaluation, boldly taking the original
designers to task (and back to a task view). A most common example of trails (literally) of
user-made artefacts is seen in the paths worn by people as they walk. Sidewalk designers
usually like to make the sidewalk patterns aesthetic – regular, symmetric, and rectilinear.
However, the most efficient paths for people getting from one place to the other are often less
tidy but more direct. The wear patterns in the grass show where people need or want to walk
and, thus, where the sidewalks should have been located. The rare and creative sidewalk
designer will wait until seeing the worn paths, employing the user- made artefacts as clues
about user needs to drive the design.
As Gaver says, when affordances suggest actions different from the way something is
designed, errors are common and signs are necessary. The signs are artefacts, added because
the designs themselves did not carry sufficient cognitive affordance. We have all seen the
cobbled design modifications to everyday things, such as padding added to prevent bruised
knuckles, a better grip taped on, an explanation written on, an important feature highlighted
with a circle or a bright colour, a feature (e.g., instructions) moved to a location where it is
more likely to be seen. Users add words or pictures to mechanisms to explain how to operate
them, enhancing cognitive affordance. Users attach yellow Post-It notes to computer
monitors and keyboards. A farmer has a larger handle welded onto a tractor implement,
enhancing physical affordance of the factory- made handle and its inadequate leverage. A
homeowner replaces the street number sign on her house with a larger one, enhancing
sensory affordance. Such user- made artefacts are a variation on the ‘user-derived interfaces’
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theme of Good, Whiteside, Wixon, and Jones [1984], through which designers, after
observing users perform tasks in their own way, modified interaction designs so that the
design would have worked for those users.
Figure 7, a photo of a glass door in a convenience store, shows an example of a user-added
cognitive affordance. The glass and stainless steel design is elegant: the perfectly symmetric
layout and virtually unnoticeable hinges contribute to the uncluttered aesthetic appearance,
but these same attributes work against cognitive affordance for its operation.
Figure 7. Glass door with a user-added cognitive affordance (arrow) indicating proper
operation
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The storeowner noticed many people unsure about which side of the stainless steel bar to
push or pull to open the door, often trying the wrong side first. To help his customers with
what should have been an easy task in the first place, he glued a bright yellow cardboard
arrow to the glass, pointing out the correct place to operate the door.
In this case, the glass had such a strong sensory effect that, although the arrow did add
cognitive affordance, it was still a bit difficult to process visually because it looks as though
it is ‘floating’ on the glass.
These trails of often inelegant but usually effective artefacts added by frustrated users leave a
record of affordance improvements that designers should consider for all their users. Perhaps
if designers of the everyday things that Norman discusses [1990] had included usability
testing in the field, they would have had the data they needed to accomplish this goal. In the
software world, most applications have only very limited capabilities for users to set their
preferences. Wouldn’t it be much nicer for software users if they could modify interaction
designs as easily as applying a little duct tape, a Post-It, or extra paint here and there?
Figure 8 below shows how a car-owner created an artefact to replace an inadequate physical
affordance – a built- in drink holder that was too small and too flimsy for today’s super-sized
drinks. During one trip, the user improvised with a shoe, resulting in this interesting example
of a user- installed artefact.
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Figure 8. A user- made automobile cup- holder artefact (used with permission from Roundel
magazine, BMW Car Club of America, Inc. [Howarth, 2002])
Another car example is shown in Figure 9, featuring a car with a rear window having a
significantly horizontal orientation. Despite the sporty styling, the design fell short in
physical affordance, leading the owner to add an after- market ‘grating’ over the window to
ward off reflections from the sun, snow from above, and other material that can too easily
accumulate on the flat window.
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Figure 9. User-added artefact to make the rear window more usable
As a final example, I occasionally need to use my desktop printer to print a letter on a single
sheet of letterhead stationery. Inserting the stationery on top of the existing plain paper
supply in the printer does this rather easily. The only problem is that I can’t easily determine
the correct orientation of the sheet as inserted, which is not obvious to me because:
1. I lack a clear mental model of how the sheet travels through in interior mechanism of
the printer,
2. printers can vary in this configuration, and
3. the design of the printer itself gives no cognitive affordance for loading a single sheet
of letterhead.
Thus, I have attached my own white adhesive label that says, ‘letterhead here, face up and
upside down’, adding yet another user-created artefact attesting to inadequate design. As
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Norman [1990, p.9] says, ‘When simple things need pictures, labels, or instructions, the
design has failed.’
5. Applying affordance concepts in usability engineering
The importance of affordance concepts to usability practitioners is in the application to
interaction design and evaluation. In our own work at Virginia Tech, we have put these
concepts to work within the usability engineering process. We have been working on
usability engineering support tools built on a common, theory-based framework called the
User Action Framework (UAF), a structured knowledge base of usability concepts and issues
[Andre et al., 2001].
5.1.
Adapting Norman’s stages-of-action model
Norman’s stages of action model of human-computer interaction [1986] had an essential
influence on the UAF, along with the cognitive walkthrough [Lewis, Polson, Wharton, &
Rieman, 1990], the structure of which is similar in many ways to Norman’s model. Both
approaches ask questions about:
•
whether the user can determine what to do with the system to achieve a goal in the
work domain,
•
how to do it in terms of user actions,
•
how easily the user can perform the required physical actions, and
•
(to a lesser extent in the cognitive walkthrough) how well the user can tell whether
the actions were successful in moving toward task completion.
Our work is not the first to use Norman’s model as a basis for usability inspection,
classification, or analysis. Several approaches (e.g., [Cuomo & Bowen, 1992; Kaur, Maiden,
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& Sutcliffe, 1999; Lim, Benbasat, & Todd, 1996; Rizzo, Marchigiani, & Andreadis, 1997])
have used Norman’s model and found it helpful for classifying and communicating about
usability problems. Even before the concepts of user- interaction design were stable and well
documented in Norman’s [1986] model, Rasmussen [1983] provided foundational support by
constructing a description of system usage in a functional abstraction hierarchy.
Norman’s stages of action model, illustrated in Figure 10, shows a generic sequence of user
activity as a user interacts with some machine in the world (annotation outside the box added
here).
Goals
Norman pointed out
need for cognitive
affordance
here; sensory
affordance also
needed here
Physical &
sensory
affordance
needed here
Intention to Act
Evaluation of
interpretations
Sequence of Actions
Interpreting
the perception
Execution of
the action sequence
Perceiving the state
of the world
Cognitive
affordance
needed here
Sensory
affordance
needed here
THE WORLD
Functional
affordance
needed here
Figure 10. Norman’s stages-of-action model (adapted with permission [1990])
Users begin at the top by formulating goals in their work domain. The goals are decomposed
into tasks and then into specific intentions, which are mapped to specifications for action
sequences. The user then executes the physical actions, causing a state change in the
physical world, which is then sensed by the user via feedback, interpreted, and evaluated by
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comparing the outcome to the original goals. The interaction is successful if the actions in
the cycle so far have brought the user closer to the goals.
Although cognitive affordance can be used to help the user with mental activities anywhere
in the top part of Norman’s diagram, Norman highlights the essential role cognitive
affordance plays on the left-hand side of this model, at the point indicated by our top- most
arrow pointing into the figure. This is the point where users map intentions into action
sequence specifications prior to making the corresponding physical actions, the point where
users most need help in knowing how to do things with a machine/computer. Mismatches
between the designer’s model and the user’s view of this mapping contribute to the wellknown Gulf of Execution [Hutchins, Hollan, & Norman, 1986; Norman, 1986]. The most
effective way for the interaction designer to help users make this mapping from intention to
action specification is with effective design of cognitive affordances (e.g. cues given by
labels, icons, and prompt messages).
The right hand side of Figure 10 is where users evaluate their actions by comparing system
feedback describing outcomes against their goals and intentions. This is the point where
users need the most help in knowing about outcomes. Since system outcomes can be seen
only through interaction feedback, mismatches between what designers provide and feedback
users need contribute to the well-known Gulf of Evaluation [Hutchins et al., 1986; 1986].
5.2.
From Norman’s model to our Interaction Cycle
As a first step we adapted Norman’s model into our Interaction Cycle (see Figure 11), which
includes all of Norman’s stages but organis es them pragmatically in a slightly different way.
Like Norman’s model, the Interaction Cycle is a picture of how interaction happens for a
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human user with any machine, in terms of sequences of cognitive, physical, and sensory user
actions.
PLANNING
ASSESSMENT
Goals
Intention to Act
Evaluation of
interpretations
Sequence of Actions
(specifications)
Interpreting
the perception
Execution of
the action sequence
Perceiving the state
of the world
PLANNING
(cognitive and
sensory actions)
TRANSLATION
PHYSICAL ACTIONS
THE WORLD
ASSESSMENT
of outcome via
feedback
(cognitive &
sensory actions)
TRANSLATION of
plans into action
OUTCOMES
specifications
(cognitive
& sensory
PHYSICAL
actions)
ACTIONS
(also sensory
actions)
OUTCOMES
Figure 11. Transition from Norman’s model to our Interaction Cycle
The linear cycle of Planning2 , Translation, Physical Action, Outcome, and Assessment
represents the simplest sequencing, common in a user- initiated turn-taking dialogue style
with a computer. Other starting points and orders of sequencing, plus gaps and overlapping,
are possible and occur in the world.
The left- hand side of Figure 11 shows how we abstracted Norman’s stages into four basic
kinds of user activities, plus Outcomes, to form our Interaction Cycle, on the right- hand side
of Figure 11: Planning of actions, Translating task plans and intentions into action
specifications, doing Physical Actions, and Assessment of outcomes of those actions.
Outcomes in the system occur between Physical Actions and Assessment in what Norman
labels ‘The World’. Because the Outcomes category does not include user actions, but is
entirely internal to the system and not part of the user interface, we show it as a ‘detached’
2
We use capitalization to indicate category names in the User Action Framework.
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segment of the Interaction Cycle in Figures 11 and 12. We found that we could associate
each observed usability problem and each usability issue, concept, or design guideline with
one or more of these categories within the context of a user’s cyc le of interaction.
5.3.
From the Interaction Cycle to the User Action Framework
We use the stages of the Interaction Cycle as the high- level organising scheme, as shown in
Figure 12 on the right-hand side, for the UAF, a hierarchically structured knowledge base of
usability issues, and concepts. The resulting UAF provides a highly reliable [Andre et al.,
2001] underlying foundation for usability engineering support tools. High reliability means
agreement among users on the meaning of the UAF and how to apply it in the tools.
Interaction Cycle
PLANNING
(cognitive and
sensory actions)
ASSESSMENT
of outcome via
feedback
(cognitive &
sensory actions)
Planning
Assessment
Translation
Physical Actions
Outcomes
TRANSLATION of
plans into action
OUTCOMES
specifications
(cognitive
& sensory
PHYSICAL
actions)
ACTIONS
(also sensory
actions)
Hierarchically structured knowledge base of usability
issues, concepts, and guidelines
Figure 12. Basic kinds of user actions, plus Outcomes, from the Interaction Cycle as toplevel structure of UAF, a usability knowledge base
UAF content under Planning is about how well an interaction design supports the user in
determining what to do with the system to achieve work domain goals and includes usability
design issues such as the user’s model of system, metaphors, and task planning and
decomposition. UAF content under Translation is about how well an interaction design
supports the user in determining how to do what was planned in terms of user actions on
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artefacts in the system, translating task plans into action specifications. Translation includes
usability design issues such as the existence of a cognitive affordance (e.g. instructive cue),
presentation of a cognitive affordance (sensory issues), content and meaning of a cognitive
affordance, and task structure and interaction control (e.g. locus of control, direct
manipulation, cognitive directness).
UAF content under the Physical Actions category is about how well an interaction design
supports the user in doing the actions. Outcomes represent the system’s reaction to physical
actions by users, computed by the non-user- interface software. This functionality provides
the functional affordances, the usefulness that fulfills the purpose of user actions. Since
Outcomes are not directly visible to users, interaction designers must provide feedback
representing Outcomes. UAF content under Assessment is about how well feedback in an
interaction design supports the user in assessing outcomes of actions.
5.3.1
UAF-based usability engineering support tools
The UAF serves as a common underlying foundation for a suite of usability engineering
support tools that we are developing. No tool has its own content; all tools draw on the UAF
in a shared relational database for contents of each node in the UAF structure. The mapping
to a given tool retains the content and structure of the UAF, but the expression of each
concept reflects the specific purpose of the tool. The UAF-based tools include the:
•
UAF Explorer tool for teaching usability concepts;
•
Usability Problem Diagnosis tool for extracting, analyzing, diagnosing, and reporting
usability problems by problem type and by causes;
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Usability DataBase tool for maintaining a life history record of each problem within a
project and for supporting aggregate data analysis such as cost-importance analysis
[Hix & Hartson, 1993] and usability data visualisation;
•
Usability Problem Inspection tool for conducting focused usability inspections,
guided by the categories and sub-categories of the UAF; and
•
Usability Design Guidelines tool for organising and applying usability design
guidelines in a systematic way.
5.3.2
Interaction style and device independence
Norman’s stages-of-action model was an ideal starting point for the UAF because:
1. it is a model of sequences of cognitive and physical actions users make when interacting
with any kind of machine, and
2. it is general enough to include potentially all interaction styles, platforms, and devices
that are likely to be encountered.
The interaction style, platform, and device independence that the UAF derives from its
theory base in Norman’s model is a long-term advantage. The UAF applies not only to GUI
and Web designs, but equally well to 3-D interaction, virtual environments, PDAs, cell
phones, refrigerators, ATMs, cars, elevators, and new interaction styles and devices as they
arise.
5.4.
Affordance roles in the User Action Framework
Affordance is perhaps the single most important overall concept in the UAF, and affordance
issues are distributed throughout the interaction design space represented within the UAF.
Cognitive, sensory, and physical actions, each with its own affordance needs in design, often
overlap significantly in direct manipulation interaction with computers, in virtual
environments, and in non-computer task performance such as in driving a car.
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When McGrenere & Ho [2000] use the term ‘degree of affordance’, they are referring to how
well an affordance works to help the user, or to the degree of usability afforded. The UAF,
via its usability engineering support tools, supports practitioners in their pursuit of high
usability, and many of the associated design issues centre on effectiveness of affordances in
helping users do things (sensing, cognition, physical actions, and functionality) within the
Interaction Cycle. Although all user types need all four kinds of affordances at some time
during usage, designs for different kinds of users emphasize different kinds of affordance.
5.4.1
Cognitive affordance in the User Action Framework
Cognitive user actions occur in Planning, Translation, and Assessment within the Interaction
Cycle and include a broad range of possibly complex cognitive processes, including rulebased cognition, habitual cognitive actions, explicit causal reasoning for conscious problem
solving, and subconscious mental activity. Cognitive affordances appear in the UAF
wherever there are issues about helping the user with these cognitive actions, such as
knowing what to do (in Planning), knowing how to do it (in Translation), and knowing
whether it was successful (in Assessment).
Design quality factors for cognitive affordance (including cues and feedback) are at the heart
of a large part of UAF content 3 , as represented by the sub-categories in Table 2.
Table 2. Representative UAF components relating to cognitive affordance quality
Content, meaning (of a cognitive affordance)
Clarity, precision, predictability of meaning (of cognitive affordance)
Precise use of words
Labels for naming a form field
Labels for buttons, menus
Concise expression
Clearly labeled exits
3
Although very stable, UAF content is subject to on-going refinement and revision to details and wording. Thus, these
tables represent a snapshot of UAF categories.
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Completeness and sufficiency of meaning (of cognitive affordance)
Complete labels for buttons and menus
Complete information for error recovery
Complete alternatives in confirmation requests
Distinguishability (of cognitive affordances)
Relevance of content (of cognitive affordance)
Convincingness of content, meaning (of cognitive affordance)
User-centeredness of wording, design of cognitive affordance content
Consistency and compliance of cognitive affordance meaning
Error avoidance (in content, meaning of a cognitive affordance)
Correctness of content (of cognitive affordance)
Make inappropriate options unavailable
Anticipate and head-off potential user errors
Request user confirmation to avoid potentially costly or destructive errors
Distinguish modes
Layout and grouping (of cognitive affordances)
Complexity of layout
Cognitive directness
Direct presentation of cognitive affordance, rather than an encoding
Cognitive aspects of manipulable objects, interaction techniques
Consistency of manipulation helps user learning
Cognitive issues of direct manipulation
Direct manipulation paradigm not understood
Cognitive affordance content to help know how to manipulate an
object, use an interaction technique
Mnemonically meaningful cognitive affordances to support human memory limits
Content, meaning of cognitive affordances for data entry
Appropriate default values for data entry
Indicate data type and format expected
Field size as indication of allowable data value length
Monospace type font (fixed width characters)
Meaning contained in cognitive affordance presentation features
Preferences and efficiency for content (meaning) of cognitive affordances
User ability to set preferences, parameters
Accommodating different user classes
Style of cognitive affordance content
Aesthetics, taste
Wording, word choice, vocabulary
Anthropomorphism, poor attempts at humor
User-centeredness in wording, design
Apparent loss of user control due to wording
Writing style, reading level (of prompt content)
Getting started in a task
An example of a cognitive affordance for Translation is a button label or a menu choice.
During Translation of intentions into action specifications, designers must ask (per Table 2)
if the choice of label wording, for example, is precise enough to provide critical clues
required for its proper operation. Is the wording comp lete enough to avoid ambiguity about
the functionality behind a button? Is the wording distinguishable from other choices and
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consistent enough to avoid erroneous user actions? Similarly, an example of a cognitive
affordance issue for Assessment is the clarity of wording in a feedback message, affecting
how well it informs users about errors occurring as the result of certain Physical Actions.
Mnemonic affordances, affordances that help users remember (supporting human memory
limitations), are a kind of cognitive affordance. Similarly, time affordances [Conn, 1995],
affordances to help users know about or understand time delays in feedback and other output,
are a kind of cognitive affordance to support Assessment.
Cognitive affordances are the most abundant type of affordance in interaction designs and
account for the most UAF content. Three out of the four major categories of user actions
(Planning, Translation, and Assessment) involve cognitive actions. Depending on work
domains and user classes, cognitive affordance arguably has the broadest and most important
role of all the affordance types in interaction design and, consequently, in the UAF. This is
because cognitive affordance is the primary mechanism to support learning and remembering
by all users except expert (error- free) users, who have automated Translation actions by
training and experience. While expert users may account for a significant percentage of
usage time, new or intermediate users comprise the vast majority of the total user population.
Even expert users of one system are novice users of many other systems.
We do not report an empirical study in this paper, but our experience from many usability
labs in many different settings in business, industry, and go vernment over the years has left a
clear impression that flaws in the design of cognitive affordances (or a lack of cognitive
affordances) account for as many as 75% of the usability problems observed, primarily in the
Translation category of the UAF. Cuo mo and Bowen [1992], who also classified usability
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problems per Norman’s theory of action, similarly found the majority of problems in the
action specification stage (our Translation part).
5.4.2
Sensory affordance in the User Action Framework
Sensory user actions occur in support of Planning, Translation, Physical Actions, and
Assessment within the Interaction Cycle. For all users except extreme experts, who can
make some actions almost ‘without looking’, each part of the Interaction Cycle generally
requires the user to sense (e.g., see, hear, feel) artefacts (including text) in the interaction
design that support the corresponding cognitive or physical user activity. Design quality
factors for sensory affordance account for significant areas of UAF content, as represented by
the categories in Table 3.
Table 3. Representative UAF content about sensory affordance quality
Sensory issues
Noticeability, likeliness to be sensed
Color, contrast
Timing of appearance of cognitive affordance
Layout complexity
Location of cognitive affordance, object with respect to user focus of attention
Focused vs. divided user attention
User focus of attention
Visibility (of cognitive affordance)
Findability
Discernability, recognizability, identifiability, intelligibility(of cognitive affordance)
Legibility of text (of cognitive affordance)
Detectability, distinguishability of sound, force
Bandwidth issues
Sensory disabilities and special limitations
Presentation medium choice (e.g., text vs. voice)
Visual quality of graphics
Auditory quality of audio
Quality of haptic, tactile, force interaction
In Planning, Translation, Physical Actions, and Assessment, UAF issues about sensory
affordances are under the Presentation sub-category (presentation, or appearance, of artefacts
used as cues, physical affordances, or feedback). As an example, font size or colour used in
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button labels and messages might affect text discernability and, therefore, legibility. Sensory
issues are separate in the UAF from issues of understanding, which occur under the Content
and Meaning category (of both Translation and Assessment).
As an example of discernability, an audio artefact such as a cautionary announcement heard
when debarking an escalator, cannot be understood and heeded if the sound is too low in
volume or the audio is garbled. As an example of noticeability, a sign in an elevator giving
information about the contents of each floor cannot be used to advantage if it is unseen
because it is posted too far above eye level. Such cases of difficult Noticeability or
Findability might be called: ‘Crouching error, hidden affordance’.
To illustrate sensory affordance in support of physical affordance, clicking on a user interface
artefact can be troublesome if the artefact is difficult to see because of poor colour contrast
with the background or if it is not noticeable because of poor location (e.g., outside the user’s
focus of attention in the screen layout) or timing of appearance (e.g., delayed or not
persistent).
An example of a sensory affordance design issue based on a real usability problem case
involves a tool palette with a large number of small drawing tool icons in a CAD system.
For expert users the icons generally did not present cognitive affordance issues; they usually
knew what at least the most frequently used icons meant. But sometimes it proved difficult
visually to pick out the needed icon from the dense group in order to click on it. This is a
sensory issue in support of Physical Actions for object manipulation, in particular a
Findability issue, owing to the overly crowded layout of the visual design. A usability
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evaluator might also suspect physical affordance issues here, too, since small size and close
proximity might make it more difficult to click quickly and accurately on an icon.
While it is important for designers to help all users see and hear cognitive and physical
affordances, special attention is required in design of sensory affordances for users with
sensory disabilities. For example, sometimes designers must build in tradeoffs between
visual and audio presentation to be selected by users with hearing and seeing disabilities.
Issues about sensory disabilities are included in the UAF, extending both Norman’s Gulf of
Execution and his Gulf of Evaluation [1986] to include sensing.
5.4.3
Physical affordance in the User Action Framework
Well-designed physical affordances support a high level of expert (error-free) user
performance and productivity – high usability for power users. Design quality factors for
physical affordances, as represented by the categories in Table 4, occur in the Physical
Actions category of UAF content, the only category relevant to helping users with physical
actions.
Table 4. Representative UAF components of physical affordance quality
Physical Actions (Design helping user do the actions)
Manipulating objects
Physical control
Difficulty manipulating an object (e.g., clicking, grabbing, selecting,
dragging)
Object not manipulable, or not in the desired way
Issues about kinesthetics of a device
Issues about manipulating a direct manipulation design
Physical fatigue, stress, strain
Gross motor coordination
Fine motor coordination
Physical layout
Proximity and size of objects as a factor in moving between (Fitts' law
issues)
Proximity (closeness) of object as a factor in ability to manipulate reliably
Proximity of objects as a factor in grouping (or sensing of grouping),
interference by unrelated objects
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Display inertia and consistency of object location
Shape of object(s)
Inconsistent location of objects
Physical object design
Interaction devices, I/O devices
Inconsistency in the way objects or devices are manipulated
Interaction techniques, interaction styles
Object not manipulable
Objects not manipulable in desirable way
Physical direct manipulation issues
Using direct manipulation when appropriate
Preferences and efficiency (for manipulating objects)
Efficiency of (single) physical actions (for MOST OR ALL users or user
classes)
Awkwardness in physical actions for MOST OR ALL users or user
classes
Accommodating different user classes and physical disabilities
Making physical actions efficient for expert users
Awkwardness in physical actions for SOME users or user classes
While expert users can ignore many cognitive affordances in an interaction design, all users
make use of physical affordances during computer-based task performance. The physical
affordance part of the UAF is about operating the ‘doorknobs of the user interface’. Of the
two main sub-categories of the Physical Action category in the UAF, sensing artefacts to
manipulate and manipulating artefacts, only the latter involves physical affordances. The
‘artefacts’ to be manipulated are the physical affordances for performing tasks. Manipulation
issues for physical affordance design include, for example, awkwardness and fatigue,
physical disabilities, power performance for experts, and ease of physical clicking as a
function of artefact size and distance from where the pointer will be for other related steps in
the associated task, according to Fitts’ law [Fitts, 1954; MacKenzie, 1992].
Physical affordance design factors also include the design of I/O devices, direct manipulation
issues, physical fatigue, and physical movements associated with virtual environments,
gestures, and interaction devices (e.g. different keyboard layouts, haptic devices, speech I/O,
and interaction using two hands and feet). Physical affordances are also particularly
important to the usability concerns of another kind of user, the disabled user. Extending
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Norman’s Gulf of Execution [1986] to include Physical Actions, physical affordance issues
in the UAF address users with physical disabilities, to whom ordinary designs can pose
barriers to physical actions. Disabled users may need assistive technology or
accommodation to improve physical affordance to allow, for example, user preferences for
larger buttons to support easier clicking by users with limited fine motor control.
The cartoon in Figure 13 is a humorous illustration of a mismatch in physical affordances
provided by designers and the physical needs of at least one class of users. Notice, too, the
tendency to self-blame by the user, a phenomenon not uncommon in similar situations with
computer users.
Figure 13. Mismatch in physical affordances provided by designers and physical needs of
users (used with permission from W. B. Park)
A computer-related example of a useful physical affordance for a physical action is the ‘snap
to grid ’ feature for precise placement of an object in a drawing program (except when that is
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not what the users want, in which case the feature is a hindrance rather than an affordance).
A classic example of a bad system feature with respect to physical affordances is
uncontrolled scrolling. In a certain word processor on the PC, dragging selected text to move
it outside text showing on the screen causes scrolling when the cursor gets to the top or
bottom of the screen. Unfortunately, the speed of scrolling is limited only by the speed of the
machine and ends up being too fast for the user to control manually. The result is thoroughly
intimidating and frustrating. The system has put the user in a difficult spot, having to hold
the mouse button depressed, with the text attached to the cursor, going back and forth unable
to find a place to put it.
5.4.4
Functional affordance in the User Action Framework
Effective functional affordance gives all users high usefulness. Design quality factors for
functional affordance appear in the Outcomes category of the UAF, the only UAF category
containing issues about functionality of the internal, non-user interface software (core
application functionality). An example of a functional affordance issue is seen in a case
where a word processor performs automatic typing correction, even against the intentions of
the user, arbitrarily changing an intended word into an incorrect word. The result for the user
is loss of control. This system behaviour definitely affects usability, but it is not just an
interaction design problem. Usability engineering developers must work with non-userinterface software engineers to modify this feature, its interface representation and its
functionality.
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5.4.5
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Affordance concepts in usability problem extraction, analysis, and diagnosis
Understanding affordance types and being aware of their roles in interaction design can help
practitioners in diagnosing usability problems observed in usability evaluation. As in design,
affordances are not the whole story of usability problem analysis. Like design, analysis
involving affordance is mostly about analysis of artefacts. The task component must also be
analysed by looking at planning support, especially task decomposition, as well as task
structure and interaction control (sub-categories under Translation in the UAF).
Usability problem diagnosis begins with observational data, raw usability data often in the
form of critical incident observations and verbal protocol, collected in a usability evaluation
setting – e.g., lab-based usability testing, usability inspection, or remote usability evaluation.
Observational data are converted to complete and accurate usability problem descriptions
through problem extraction, analysis, and diagnosis, in which consideration of affordances
plays a major role.
As an example, consider the following usability problem from a real- world usability lab.
A user thinks he knows what he is doing on a certain task, but when he selects an object
and clicks on an icon, he gets an error message. The user complains that the error
message is in a very small font and the colour is too close to the background colour, so he
has difficulty reading the message.
Since this case statement is about a message, which is an interaction design artefact, it is
appropriate to use affordance concepts to guide the analysis. Questions such as those in
Table 5 below (skipping those for Planning in the UAF for now) can help pinpoint the
diagnosis:
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Table 5. Example affordance-guided problem diagnosis questions
1.
2.
3.
Was the trouble in determining which icon to click on (Translation)?
a. Was the trouble in seeing the icons, and labels (sensory affordance in support of
cognitive affordance)?
b. Was the trouble in understanding the meaning of the icons and labels (cognitive
affordance in Translation)? Was user confused? Did user make an error?
Was the trouble in doing the clicking (Physical Action)?
a. Was the trouble in seeing the icon in order to click on it (sensory affordance in
support of physical affordance)?
b. Was the trouble in doing the clicking quickly, easily, and reliably (physical
affordance)?
Was the trouble in determining if the outcome of the action was favorable (Assessment) and,
if something went wrong, in determining what went wrong?
a. Was the trouble in seeing, discerning the feedback message text (sensory affordance
in support of cognitive affordance for feedback)?
b. Was the trouble in understanding the feedback message content or meaning?
Our example case indicates two possible usability problems. The display of an error message
clearly shows that an error must have occurred. When a critical incident arises due to the
occurrence of an error and nothing is wrong with the resulting message, the focus is on the
error itself and its causes. This is in the Translation (of plans to action specifications)
category of the UAF and in question 1 of the table, since this category is about cognitive
affordances that help the user determine correctly how to do something and to avoid errors.
However, in our current example the user’s complaint is about the quality of the message, not
the occurrence of the error itself, so we answer ‘no’ to question 1 in the table for this
particular problem. However, the problem of the error occurring is retained and becomes a
separate implied problem to be extracted and its diagnosis will require further data (about
what happened earlier, probably a cognitive affordance failure, to cause the error).
The physical action of clicking was not an issue, so we answer ‘no’ to question 2 in the table,
but we must answer ‘yes’ to question 3, which is about feedback and Assessment. An
Assessment problem can be about Presentation of feedback (where sensory aspects are found
in the UAF, relating to question 3a), including such issues as feedback Noticeability,
Discernability, Timing of appearance, and Graphical quality. Or it can be about feedback
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Content and meaning (where cognitive aspects are found in the UAF, relating to question
3b), including such issues as feedback Clarity, Completeness, Correctness, and Relevance.
The problem case statement says that the user has difficulty reading the message, which can
be ambiguous. An inexperienced practitioner might be tempted to skip further analysis and
jump to the conclusion that this about the user not being able to read the error message in the
sense of being unable to understand it completely, a common kind of cognitive affordance
problem in Assessment. However, the wording of the case statement makes it clear that the
problem is about the user’s inability to discern the text of the message; the user cannot easily
make out the characters in order to read the words. The problem now comes into focus as a
sensory affordance problem in the feedback design, found in the UAF under Assessment,
Feedback issues, Presentation of feedback, and Sensory issues of feedback. The problem
diagnosis is further traced in the UAF to Discernability, and then Legibility of text and then
to Font colour and contrast (with background).
Accurate diagnosis is essential to fixing causes of the right problem, the problem that
actually affected the user. Different problems, involving different types of affordance,
require entirely different solutions (e.g., changing the font size vs. changing the message
wording). It is important for practitioners and developers to understand the distinctions,
which are often best understood in terms of affordance concepts. Fixing the wrong problem
can waste resources and leave the original problem unsolved.
Not fixing all the problems can lead to missed opportunities. For example, improving only
the cognitive affordance to avoid the error should make this problem occur less frequently,
but would leave the error message problem unsolved for those times when the error does
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occur. Revising the expression of the meaning in the error message might be an
improvement, but would not solve this sensory affordance problem.
Finally, data visualisation based on affordance types can be used to improve a usability
engineering process. This kind of usability data visualisation requires storing records of
usability problems for a project in a database with affordance-related attributes. We use our
UAF-based Usability DataBase tool, within which each usability problem is stored, having
been diagnosed by problem type and causes among UAF categories. We then tag nodes of
the UAF with their associations to each affordance type and are able to visualise the usability
data as clustered by affordance type. While the interpretation of clusters is an open question,
a large number of usability problems involving the meaning of cognitive affordances would
seem to imply design shortcomings involving precise use of words, semantics, and meanings
of words and icons – shortcomings that might be addressed by hiring a professional writer,
for example, to the interaction development team.
Similarly, large numbers of problems involving physical affordances are a possible indicator
of design problems that could be addressed by hiring an expert in ergonomics, human factors
engineering, and physical device design. Finally, large numbers of problems involving
sensory affordances might be addressed by hiring a graphic designer or layout artist. Formal
studies will be required to validate the hypotheses behind these expectations.
6. Conclusion and future work
We agree with Norman’s concern that the term affordance has been used with more
enthusiasm than knowledge. Perhaps the concepts associated with affordance are so natural
and so necessary that people either couldn’t resist implicit, undeclared extensions or they
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may have believed that the kind of extensions we propose were already accepted usage. We
have proposed and explored the use of the complementary terms, cognitive affordance,
physical affordance, sensory affordance, and functional affordance to refer to the
corresponding concepts in interaction analysis and design. We think an independent concept
of cognitive affordance is equally important as the concept of physical affordance. It is a
good match and a parallel to physical affordance and is essential to interaction analysis and
design, as Norman himself has pointed out many times. We also think that sensory
affordance is necessary to support cognitive and physical affordance throughout the user’s
Interaction Cycle.
In order to get the most practical utility from the concept of physical affordance, we have
proposed that each reference to it by researchers or practitioners appear with a statement of
purpose, which should be supported by functional affordance in the non-user interface
software. Finally, we have developed the UAF to connect these and other interaction design
concepts in the domain of design and analysis for usability.
We hope that the suggestions here will bridge the gap between Norman’s concerns about
misuse of affordance terminology and the needs of practitioners to use the concepts in a
practical way. Now usability researchers and practitioners can refer unambiguously to all
four types of affordance in the context of interaction design and analysis.
We have explored the relationship between the affordance types associated with observed
usability problems. Practitioners can apply usability case data to identify where affordance
issues are involved in flawed designs and produce case studies of how increased attention to
affordances can improve interaction design.
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Acknowledgments
Many thanks to Donald Norman for helpful comments on an early draft and his
encouragement to pub lish this article and for his permission to use the diagram of his model
in Figure 10. Thanks also to Roger Ehrich, for traveling all the way to Austria to bring me a
gift of the wine opener in Figure 2 and for pointing out the user- made artefact as automobile
cup holder in Figure 8. Thanks to my colleagues in UAF development, Terence Andre,
Steven Belz, and Faith McCreary, for their inputs about affordances over the past few years,
and to Deborah Hix for reading the manuscript and making useful suggestions. I’m grateful
to Tonya Smith-Jackson for reading the manuscript and making several valuable suggestions.
In particular I thank Tonya for helping with terminology, especially the term sensory
affordance. Similarly, I wish to thank Elizabeth Buie for several insightful and practical
discussions about concepts and terminology involved in sensing, perception, and cognition.
I also wish to express my appreciation to John Karat, North American Editor in charge of this
paper, and the anonymous BIT reviewers for supporting publication of this as a concept
paper in the face of increasing demand for papers on methodologies and empirical studies.
Special thanks to Jeff Weinberg for helping me locate the Gaver papers [1991] and for
pointing out McGrenere and Ho [2000], two important references on affordance. Thanks
also to Steve Belz and Miranda Capra for examples of false affordances.
Finally, all photos were taken with a small consumer- grade digital camera (brand to remain
unnamed to protect the guilty) from our Usability Methods Research Laboratory that has its
on-off power switch where most cameras have their shutter-release button. On more than
one occasion, after struggling with multiple menus to configure the camera setting just right,
at the precise moment of capture, this design ‘affordance’ has led to my unintentionally
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shutting off the camera. Further, each time I turn on the camera power, the lens telescopes
out, knocking the lens cap off onto the ground (or worse). Let’s hear it for good design!
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