Illusion, Delusion, Collusion, and Perceptual Paradox (page 1)
Illusion, Delusion, Collusion, and Perceptual Paradox
twinkling of an eye, and the boxes on the floor
Hang from the ceiling. Really they are not boxes,
But only certain black lines on white paper,
(The programme of an hour of magic and illusion)
And, but for the eye, not even black on white,
But a vast molecular configuration,
A tremor in the void, discord in silence.
Boehme agrees with Jasper Maskelyne
That all is magic in the mind of man.
The boxes, then, depending on my mind
Hang in the air or stand on solid ground;
Real or ideal, still spaces to explore:
Eden itself was only a gestalt.
My house, my rooms, the landscape of my world
Hang, like this honeycomb, upon a thought,
And breeding-cells still hatch within my brain
(And still the bees will have it that the earth has flowers)
But the same dust is the garden and the desert.
Ambiguous nothingness seems all things and places. "
Kathleen Raine (Raine, 1956, p. 93)
Fig.6.1 Stare at this square for about
a minute in order to observe an afterimage. If you look at a distant
wall after impressing afterimage on your retina, image will appear to
be larger than if you look at a surface much closer to you.
The pictorial effects we have been discussing all fall into
the broad category of illusion. It is the purpose of this chapter to shed
some light on the experience one can have when confronted with objects that
fall under this rubric. The Oxford English Dictionary defines "illusion"
Sensuous perception of an external object, involving
a false belief or conception: strictly distinguished from hallucination,
but in general use often made to include it, and hence equals the apparent
perception of an external object when no such object is present, or of attributes
of an object which do not exist. (1971 compact ed., s.v. "illusion")
One of the best-known examples of such a perception is
called the moon illusion, the impression that the moon is larger when
it is close to the horizon than when it is close to the zenith. Lloyd Kaufman
and Irvin Rock confirmed in 1962 a theory that has been attributed to Ptolemy,1
to wit, that the moon appears larger on the horizon than at the zenith because
the filled space between the observer and the horizon makes the horizon seem
further than the zenith2 (Kaufman and Rock, 1962; Rock and Kaufman,
1962). There is an implicit inference here that is based on the following law:
All other things being equal, the further away an object (of constant angular
subtense) seems to be, the larger it will appear to be.
An especially pure example of the operation of this law was discovered by Emmert,
in 1881. It is also easy to demonstrate. Look at the black square in Figure
6.1 for about a minute. When you look away, you will see a dark spot in front
of you; this dark spot moves as you move your eyes, because it is caused by
the neurochemical process by which the photosensitive cells in your retina recover
from the unusually prolonged exposure that they sustained. Because this effect
is impressed on the tissue of the retina itself, it must move with your eyes.
At first blush, it may seem surprising that such a purely internal activity
feels as if it were located outside vote; but that is a general rule in perceptual
systems: If one stimulates sensory receptors in a nonstandard fashion, one invariably
experiences an external object that would stimulate the sensory receptors in
a similar fashion.
Now this sort of effect on the retina could just as well have been caused by
a distant large square or by a close small one. Because an afterimage does not,
so to speak, remember the distance of the page on which the stimulating square
was printed, the size and distance of the black square that one experiences
when having an afterimage would remain indeterminate were it not that perceptual
systems abhor indeterminacy. (Try to think of what a square of indeterminate
size and distance would look like.) To forestall such indeterminacy, the visual
system uses the best available information about the size and the distance of
the square: It assesses the distance of the surface at which the observer is
currently looking, and, using that information and information about the size
of the afterimage on the retina, it computes the size of the square to be seen.
So if - after you have impressed an afterimage on the retina - you look at a
distant wall, the square will look large; and if you look at a sheet of paper
that is close to you, the square will look small. We can now state Emmert's
law: The apparent size of the object you see when you experience an afterimage
is directly proportional to the perceived distance of the surface at which you
The moon illusion and Emmert's law are both examples of an important way in
which perceptual systems are endowed with the ability to perform what Helmholtz3
called unconscious inferences, an idea that is central to what I wish
to say about illusion and art in this chapter.4
Do we ever use the term "illusion" in the sense that applies to the
moon illusion when we apply it to art? I think not: I do not think there ever
is "false belief or conception" when we look at a work of art. Arthur
C. Danto's discussion of illusion (in the sense of false belief or conception)
shows clearly why we should hold this view:
If illusion is to occur, the viewer cannot be conscious of any properties
that really belong to the medium, for to the degree that we perceive that
it is a medium, illusion is effectively aborted. So the medium must, as it
were, be invisible, and this requirement is perfectly symbolized by the plate
of glass which is presumed transparent, something we cannot see but only see
through (as consciousness is transparent in the sense that we are not conscious
of it but only of its objects)... So conceived, it is the aim of imitation
to conceal from the viewer the fact that it is an imitation, which is conspicuously
at odds with Aristotle's thought that the knowledge of imitation accounts
for our pleasure. But imitation evidently did not entail illusion in Aristotle's
scheme. In Plato's it evidently did, and it is this form of the theory I am
working with now. Taken as a theory of art, what imitation theory amounts
to is a reduction of the artwork to its content, everything else being supposedly
invisible - or if visible, then an excrescence, to be overcome by further
illusionistic technology. (1981, p. 151)
I take it for granted that the reader agrees with Danto's claim that the artwork should not be reduced to its content, or else that he or she will read his persuasive argument in Chapter 7 of The Transfiguration of the Commonplace.
Fig.6.2 A classification of trompe l'
The only works of art that come close to exemplifying this sort illusion are
the illusionistic architectures we discussed in the preceding chapter and trompe
l’œil paintings. To better understand the role of illusion in
art, let us examine this interesting aberration art. I have classified the illusionistic
paintings that go under the name trompe l'oeil (eye foolers) in Figure
6.2. The pictures fall into two major groups according to what the artist has
1 Claudius Ptolemæ us, a second-century
astronomer and geographer who lived in Alexandria, author of the Almagest.
2 The Kaufman-Rock theory has been challenged by Baird (1982), Baird
and Wagner (1982), and Hershenson (1982) textcolorgreenREVIEW LITERATURE Kaufman
L, Kaufman JH. Explaining the moon illusion. Proc Natl Acad Sci U S A. 2000
Jan 4;97(1):500-5. Iavecchia JH, Iavecchia HP, Roscoe SN. The moon illusion
revisited. Aviat Space Environ Med. 1983 Jan;54(1):39-46. Coren S, Aks DJ.
Moon illusion in pictures: a multimechanism approach. J Exp Psychol Hum Percept
Perform. 1990 May;16(2):365-80. Plug C, Ross HE. The natural moon illusion:
a multifactor angular account. Perception. 1994;23(3):321-33.. It is too early
to determine the extent to which this new research will force a revision of
Kaufman and Rock's theory. In any event, the purpose of the present discussion
is to clarify the notion of unconscious inference and to set the stage for
thinking about the nature of illusion. My argument does not hinge on the survival
of any particular theory.
3 One of the great physicists and psychologists of the nineteenth
4 For a contemporary presentation of the theory of unconscious inference,
see Rock (1977 and, especially 1983).