More on Affordances
J. J. Gibson, Cornell University; March 1971
This memo has been published in E.S. Reed & R. Jones (Eds.) (1982). Reasons for Realism. Chapter 4.9, Parts III (pp. 406 - 407) and IV (pp. 407 - 408). Hillsdale, NJ: Lawrence Erlbaum Associates, Inc.
At one extreme stands the fact that educated adults have a conception
of space, i.e., mathematical or geometrical space, Euclidean, Cartesian,
non-Euclidean, etc.
Then there is what psychologists have called the perception
of space. Although it is a complete muddle, and full of contradictions, depth-perception
implies distance-from-here, and such perception recognizes at least the fact
of a potential observer and a surrounding space.
Next there is what I call the perception of layout - the actual
layouts of environmental surfaces, chiefly opaque solid surfaces, and the geometrical
components of layout. Such perception depends on optical information
for environmental places and objects at the set of all possible points of observation
in the medium, and this takes into account both hidden an (unprojected) and
unhidden (projected) surfaces at a fixed point of observation.
Finally, at the other extreme, there is the perception of the affordances
of environmental surface layouts (which include objects and places and even
animate objects). The activity of an observer that is afforded
depends on the layout, that is, on the solid geometry of the arrangement. The
same layout will have different affordances for different animals, of course,
insofar as each animal has a different repertory of acts. Different animals
will perceive different sets of affordances therefore. The perception is of
practical layout, not theoretical layout,
but it is nonetheless geometrical for all that. Animals, and children until
they learn geometry, pay attention to the affordances of layout rather than
the mathematics of layout. Hence, although logically one advances from space
to affordance, developmentally the progress is in the opposite direction, from
affordance to space. The formless invariants in the light which
the eyes of the very young pick up, instead of the forms of the visual field,
are just those that specify affordances.
Still More on Affordances
There has been a great gulf in psychological thought between the perception
of space and objects on one hand and the perception of meaning
on the other. But when space and objects are defined in terms of t he opaque
solid geometry of surface layout, and when meaning is defined in terms of the
affordances of places, substances, surfaces and objects (hereafter termed "things"),
these problems are seen to be linked. For example, what anything affords an
organism depends in some degree on its shape or the features of its shape (solid
shape, of course, not pictorial form). Hence it is that the shape of something
is especially meaningful. The meaning or value of a thing consists of what it
affords. Note the implications of this proposed definition. What a thing affords
a particular observer (or species of observer) points to the organism, the subject.
The shape and size and composition and rigidity of a thing, however, point to
its physical existence, the object. But these determine what
it affords the observer. The affordance points both ways. What a thing is an
d what it means are not separate, the former being physical
and the latter mental as we are accustomed to believe.
The perception of what a thing is and the perception of what it means are not
separate, either. To perceive that a surface is level and solid is also to perceive
that it is walk-on-able. Thus we no longer have to assume that, first, there
is a sensation-based perception of a thing and that, second, there is the accrual
of meaning to the primary percept (the "enrichment" theory of perception, based
on innate sensations and acquired images). The available information for the
perception of what it affords.
The controversies over whether the values of things are "relative" or "absolute,"
and whether value is a subjective phenomenon or an objective fact, should be
reinterpreted in the above terms.
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