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Department of Psychology,
University of Glasgow.
There have been discussions on what J.J.Gibson means for visual perception,
for the notion of affordance in HCI, and for the notion of affordance in
e-learning. We all have enormous trouble integrating his ideas with our
habitual ones, and the more we are trained (indoctrinated) in computer
programming and reductionist "science" the more trouble we have. A number of
authors have attempted to define and redefine terms like "affordance".
Normally, I am strongly drawn to this kind of approach. But the trouble is
that when we attempt to define a term, we fall back almost entirely
unconsciously on existing patterns of thought, and do not even consider giving
up anything we already believe. Gibson however constitutes a challenge to
some of our patterns of thought.
I think the simplest short thing we can do is to list some basic lessons
Gibson taught: whenever we write something inconsistent with these, then we
are showing our prejudices in ways that are incompatible with the real
world (as well as with Gibson's ideas, which aren't necessarily right in all
ways). Here's my list of such Gibson inspired points, or facts.
- Optic array: Almost all work on human perception, past and present, analyses
it by sense organ or modality. But our actual perception works by integration
not only of multiple sense organ inputs but also of our motor system with our
perception. If you press your eyeball, the world seems to move (because if you
don't send the signal to move the eye yourself, then the integration goes
wrong). At a larger scale, we walk round objects (but retain an integrated
percept of a single object), or rotate small objects in our hand. We move our
eyes through the optic array in order to sample different parts of it and so
pick up more information, like a dog zig-zagging across a scent trail to
determine from which direction it is coming from: perception and active
sampling motion are a single system in real organisms (though not in most
labs). It is unjustified philosophical prejudice, not science, that makes most
of us analyse perception and action separately. In real life they are
fundamentally integrated at the lowest levels.
- Optic flow. One of the things our perception does is recognise objects, but
it does other things which do NOT depend on recognition. We control our
locomotion (whether by foot, or in driving a car) based on the flow of visual
texture fields in our field of vision, and our brains compute information on
our motion without having any knowledge of the nature of the flecks of texture
(e.g. dirt on the window, patterns on the ground, ...). The optic flow field
gives us the value of the variable "time to collision" directly without our
knowing (even unconsciously) the distance to the object we are approaching.
This is why anyone can drive a car, and can do so with very bad depth
perception. Our prejudices and education predispose us to make up a story
about how we recognise the car in front as a car, compute the distance to it
using "depth perception" (parallax, stereopsis, etc.), estimate our speeds,
etc. None of this turns out to be a correct description either of the
function actually performed by our perception or of the mechanism that
- Intermediate states do not have a meaning in the way that final percepts
do. Optic flow and time to collision are one case where the intermediate
computational states are not those you might expect, and in particular do not
correspond to things in the world: they are internal states with less meaning
than a carry digit isolated in the middle of a piece of arithmetic. But this
general point comes up much more pervasively in computation, even though it
goes against our strong intellectual preferences to understand calculations as
putting together parts each of which are meaningful in the same way as the
whole is. For instance, the kind of story we like is that we recognise a duck
because we recognise a duck-like head next to a duck-like body and wings, and
recognise the whole by virtue of first recognising the parts. But even in a
world of information, this is not generally true. Information, technically,
is a reduction of the number of alternative possibilities in a situation. For
example, consider that you are recognising capital letters, and then that the
first bit of information you get is that the right hand side is a vertical
line. This reduces the possible identities of the letter from 26 down to one
of [H, J, M, N, U]. We do not have a (conscious) concept that represents that
subset of letters, but the recognition system must have such an internal state
and many others of that kind, each representing a different increase in
partial information; but these have no correspondence in the world of letters
- Direct perception. Gibson seemed to deny that there were any intermediate
states or computation in perception. Of course there are if we want to
analyse things that way (and I do): but these states have no meaning
correlates themselves in the outside world. Furthermore, the real point here
is that the phenomenon of perception could and should be described as a
function from properties of the world to percepts with no reference to the
internal computational intermediate states. This shows a clarity of thought,
a realisation of what is primary in understanding perception. This is exactly
parallel to the way that Darwin defined evolution with no concept or knowledge
of genes, let alone of DNA. Genes are one implementation or mechanism for
evolution. Evolution is the primary theory and does not require genes.
Gibson formulated perception as a function from world to percept: not
muddling it up with possible mechanisms. One of the worst, but most
pervasive, intellectual vices is to assume that mechanism is primary. An early
example of this fallacy were those who dismissed Newton's theory of
gravitation for being "action at a distance" that didn't satisfy their
irrational desire for a mechanism transmitting the force through intermediate
- Affordance. Gibson's basic notion of affordance links action and perception
the other way round: suggesting that (because beings in general and people
in particular are concerned with acting in the world) we perceive as a direct
attribute the actions we might perform with or on each object. This is a
surprise only to those who presuppose (without evidence) that perception is
independent of action, and is prior to it. It may also be a surprise to those
who think perception is about measuring the absolute attributes of objects,
because affordance is obviously not an object attribute, but a relationship
between object and perceiver. But in fact (contrary to our habitual but
faulty thought patterns), perception, like measuring, primarily and more
easily detects relationships. Even when we are measuring an object carefully
with a ruler, we are using our perception of the object's relationship with
the ruler to derive an "absolute" property.
- The perception of novel objects and situations. There has been frequent
discussion of whether Gibson denied or took insufficient account of the role
of learning in perception. It is perhaps more important to ask whether most
research on perception puts too great a weight on it. If we consider object
recognition, then by definition a perceiver cannot do it until they have
encountered the object, perhaps frequently. Yet an infant animal would
presumably die immediately if learning had to precede successful perception
and action. In the real world, beings encounter unknown objects all the time
and a large part (in fact most?) of perception concerns what and how we
perceive unknown objects. In designing artifacts and user interfaces, this is
a chief concern: can a user operate a novel device first time, without
training? This is the context in which most discussions of affordance in
design are situated.
- Success without understanding. In design, the mindset which designers
must escape is the assumption that successful action (such as operating a new
device) depends on knowledge which is obtained from prior training, and that
it is patronising to think that some users cannot master this. Contrary to
this, a user centered approach sees learning as a cost and a burden that good
design should avoid. Indeed, published experiments illustrate how in
situations where information is rich, users still haven't learned what to do
after many trials: they simply rediscover it on the spot each time. The aim
of design in most cases should be to avoid the need for learning and indeed
for thinking, and to aim for users to operate in "flow" from the start. While
understanding is a pleasure, it is not the pleasure being sought when users
try to open a door or operate a tool to do something else. The use of the
concept of affordance in design is to allow users to perceive what to do
without learning. When a door has no handle but a push plate, this is
achieved. When an on/off switch has no label and a delay before any effect is
visible, it is not, since the user cannot tell whether to press once, twice,
or to hold down the switch.
- Human analogical machinery.
Whenever someone sees anything, the thing is always to some extent novel: the
day is different, the time, the phase of the moon, the lighting; if it is a
person then their clothes are different, many of their cells have been
replaced, etc. When it is a novel object, the differences are greater. But
fundamental to perception in fact is deciding what this new stimulus is most
like. When faced with a novel artifact or user interface, and (as is almost
always the case today) the assumption that they will try it out without
reading any instructions, then the big question is: what is this thing most
similar to, which analogy will the user implicitly and unconsciously draw?
Current computation has no impressive mechanisms for this, but human minds are
fantastically good at it, yet it is little studied. Why will one situation
(design) trigger an association, and with it, user behaviour? A few
unpublished examples however suggest that these associations are not always
and reliably predicted by our conscious categories. That is why almost the
only thing we know about HCI is that we have to observe actual users on
particular designs: we cannot adequately predict their response.
One such example from a computer system long ago in a country far, far
away is as follows. The command for listing the emails in the inbox was "ha"
(Headers All); and the command for listing the files in the current directory
was "ls". Not particularly frequent, yet persistently repeated, was the user
error of sometimes typing "ls" for "ha" or vice versa.
How could these two be confounded in the user's mind? The command names, the
documentation, the nature of the objects (file names versus emails) were
different in anyone's ontology, especially that of the technically experienced
users exhibiting this error. This kind of error seems to reveal hidden,
tacit categories (e.g. approximately "show me my bag of things") that have the
power to determine user behaviour.
- Learning isn't fundamental to perception: dealing with novelty is.
A more fundamental mechanism is analogy: recognising partial similarity
Learning will be most important toi perception where it is about learning
to do this more effectively
The most important things for an organism (to learn) to perceive are not
objects but actions the agent can achieve: i.e. affordances.
Comments, HCI, Education
Oliver, Dohn and others have commented on the problems with people's
definitions of "affordance" in the fields of HCI and Education (especially
technology and education).
They try to do conceptual analysis, and to connect the concept with
philosophical concepts. I'm going to leave them to it because I don't find
their papers illuminating of educational issues. Following my comments above
I'm going to:
- Ask why/how "affordance" seems relevant to education
- Suggest which points from above or elsewhere might actually illuminate
education, and avoid conceptual errors relevant to our understanding of
- Good examples in HCI of affordance are things like the way Apple and
others carefully designed floppy discs so that they could not be inserted the
wrong way in disk drives (even though there are 8 ways a perfectly square disk
could be inserted). On some doors in our public buildings today, there are
no handles, only plates: so without thinking (and regardless of whether you
use vision, touch, or just trial and error) everyone knows you can only push
- A good example in education of affordance is something like the way a
child or a student will seize the opportunity, when they have a mentor in a one
to one situation, of asking endless questions: that is what access to an
expert affords us. Students will also, if and when they have the opportunity
with friends they are comfortable with on the same course, compare the
marks and feedback they get. (Only by talking to students did I finally grasp
that this gives them information they can't otherwise get.) Similarly they
are deeply interested, when it is available, in seeing their ranking compared
to their peers; how other students have answered an assessed task, and so on.
Again, most teachers (and published theories of learning and teaching) are
oblivious to why they do this. By observing affordances and their uptake by
learners, things otherwise invisible to us as teachers begin to manifest. They
can tell us about what the needs of our students are (we often are only aware
of the goals we tell them to have); and about how they can satisfy them (when
mostly we only think about what we provide, not what may be there all around
them). This is not only a remedy for the teacher-centeredness of most
educational thinking, but it is also (just like Gibson) like what faces
biologists: believing in Darwin does not in itself give any clues to what
needs an organism has nor to how they may often be supplied by its niche
(often quite invisibly to us).
- A bad example of affordance in education is to say a lecture affords
listening and/or learning. This is both trivial and wrong. It is trivial
because it is what teachers think, not an insight into actual learning. It is
wrong because actually a lecture only affords that to those learners who speak
the same language, who can hear clearly, and who don't already know everything
that is said.
Affordance, as I (following Gibson) said above, is NOT a property of an
object but a relationship between a person, an object, and a
goal/task/function the person has.
- Interestingly this type of misconception is manifest in several other
places in education. One is due to Carroll and Bloom and associated with
mastery learning. Carroll pointed out (and supported by experiments) that
even though most of us still today interpret the spread of marks in a class as
telling us about an attribute of the learner, in fact there is again a 3-way
relation between the learner, the material, and time: almost all learners can
learn all the material but take different amounts of time to do so. This
mis-interpretation by teachers leads to endless needless under-performance.
Again, deep and shallow approaches to learning are NOT traits of the
learner, but a relationship between that learner, that learning context, and a
strategy or approach; learners select their approach depending on the context,
they are not stuck with one approach for all things.
- Assuming that what is actually a 3-way relationship is merely a 2-way,
object-attribute property is pervasive. Psychologists call a common form of
this the "fundamental attribution error", where a person explains a problem or
failure in terms of the properties of another person. The e-learning field is
particularly prone to this, where talk of early adopters vs. resisters is
exactly this (mis-)attribution: and a failure to grasp that the "contexts" of
different people are different, so that the value or feasibility of adoption
of the same equipment just is different for different people, and is
not a constant property of the technology independent of people. Reversing
this by being user-centered would attribute the failure to the designer not
the end-user thus combatting the self-serving basis for most such
attributions; but it would still not tackle the common reality that some things
work for some people but not for others: i.e. it is not about a single
artifact with absolute properties regardless of the user.
- Norman said he would replace all occurrences of "affordance" in his book
by "perceived affordance". I however have another view. A design which
novices and experts alike find immediately usable is one thing; designs
which require learning investment from users are another. Both are important;
and again, the important point for designers is that the desired feature is
NOT a function (attribute) of the design/object alone, but of the 3-tuple of
user, object, and goal/function. This too has an important similarity with
learning designs where in general designers (i.e. teachers designing a course
or a lesson) are even worse than software designers at thinking clearly about
this, about the fact that a given design will only work for learners who
already have certain skills and will fail for others. Lectures, for example,
only afford learning for learners who not only can hear and understand the
words, and who want to learn about the topic, but who have skills (e.g.
note-taking) that are comparable to an experienced user's knowledge of how to
get writing done with a word processor. All learning designs have
pre-requisites of not only teacher skills but of learner skills: that is one
big reason why learning designs seldom transfer to all other contexts.
- Thus taking into account the cost of learning the skill of using
something for a goal i.e. of changing the human agent so that the object now
does afford them an important function, is an issue that is important but
often missed in both HCI and education and indeed other fields. Thus learning
is frequently an important cofactor for affordances. Many published
commentaries on affordances debate whether Gibson would agree with this. A key
point here is that this "learning" is quite different in kind from the
learning most of us mean when we discuss education. In education we almost
always expect and test what the learner can articulate, write about, and teach
to someone else. But with affordances, someone who can do it may be unaware
that they have learned anything, unable to describe what it is they know, or
to pass it on to someone else. There are huge differences in effectiveness
between teachers, as measured by the attainments of their students. This is
correlated with their experience (i.e. the amount of their tacit learning).
But they generally can't pass it on to others, or training would homongenise
this effect away. In HE, some untrained tutors exhibit great skill at
facilitation, while others who have been "trained" are vastly less effective.
These effects are large, important, and not understood; they can in one way
reasonably be described as "learning" yet they share few characteristics with
the "learning" that organised education purveys. Quibbling about what
"learning" means may interest philosophers. For those interested in
understanding education, we should recognise that some aspects of Gibson's
mindset illuminate issues which are dangerously ignored or neglected in most
educational literature, and so are worth paying attention to.
- To get value for understanding teaching and learning from Gibson and the
notion of "affordance", we need to immerse ourselves in that way of looking at
things: success without understanding, picking up information that is lying
around us, using it without remembering it, being able (or not) to do things
without any idea why we just succeeded or whether that success will generalise
to other times and places. Both teaching and learning have a strong
dependence on unidentified skills of this kind. The ideal learning designer
would be able to reason about this, but faces the same difficult research
programme as do biologists who have not yet discovered bat sonar or the use by
some organisms of the way light is polarised to detect where north is or the
electric fields picked up by fish; or planetologists working on the "Gaia"
theory that there are hidden self-correction mechanisms maintaining earth.
In this view, the operation of teaching and learning depends in part on
mechanisms we cannot see and do not yet even suspect the existence of. Alerted
by Gibson's way of thinking, I have noticed many clues over the years that
seem to support this view.
Gibson's ideas thus give us 4 useful things for pushing forward our ideas about
- We use the one word "learning" to refer to two quite different things:
what is expressed learning objectives and tested in exams, and the often
unconsicous changes in behaviour and capability that experience sometimes
causes. This is pernicious not just as a conceptual muddle, but because when
focussed on one meaning we forget to check whether the simultaneous operation
of the other is crucial to the case being studied.
- A reminder that treating 3-way relationships as simple 2-term
object-attributes is pernicious but very common.
- The notion of affordance can remind us to look, not at what things are
officially designed for (chairs for sitting, not rocks; sticks are for trees or
perhaps poking things, but not for termite fishing), but at what people
(learners) actually do with opportunities. This reveals to us something about
the needs they actually feel, not the ones we intend them to have; and the
methods they actually use to satisfy them, not the ones we so kindly designed
- On the other hand, just as learners / people are more flexible than we
expect in some ways, they are less flexible than we assume or wish in other
ways. Especially in the short term, we have to allow for the costs of
learning how to learn.
Benjamin S. Bloom (1984) "The 2 Sigma Problem: The Search for Methods of Group
Instruction as Effective as One-to-One Tutoring"
Educational Researcher Vol.13, No.6, pp.4-16
Carroll, J.B. (1989) "The Carroll model: A 25 year retrospective and
prospective view" Educational Researcher vol.18 no.1 pp.26-31.
Dohn, N.B. (2009) "Affordances revisited: Articulating a Merleau-Pontian view"
Computer supported learning vol.4 pp.151-170
Oliver,M. (2005) "The problem with affordance" E-learning vol.2 no.4
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