 | 9 The psychology of egocenters The psychology of perspective and Renaissance art |  |
9 The psychology of egocenters
their definition, and expresses only my incomprehensible solidarity
with one of them — my body.
Maurice Merleau-Ponty, from “Eye and mind”
(1964, p. 173)
I have mentioned several times the idea that, when we
perceive a picture drawn in perspective from a vantage
point other than the center of projection, our perceptual
system infers the location of the center of projection and
we feel that we are looking at the depicted scene from the
vantage point implied by the center of projection. To explain
the meaning of such a suggestion, I must first introduce
the concept of egocenter. I will then discuss the question
of a movable egocenter.
The notion of a spatially localized, visual egocenter that
does not coincide with either eye is due to W. C. Wells
(1792, cited by Ono, 1981), who was the first to devise a
way of locating what came later to be called the “cyclopean
eye.” One simple method is this: Hold your head still while
a friend stands a few feet away and points a stick at you.
Have the friend change the position of the stick until you
feel it pointing at you perfectly. Record the exact orientation
of the stick. Now without moving your head ask
your friend to stand somewhere else in the room, to the
right or left of where he or she stood before, and adjust
the orientation of the stick until it is pointing at you. If
you do this several times, and you prolong the lines defined
by the various positions of the stick when it is pointed at
one point inside your head just behind the midpoint of the
line connecting your two eyes. This is the position of what
is sometimes called the sighting egocenter (Howard, 1982,
pp. 283–91).
In his philosophical essay “Where am I?”, which may
be the most amusing science-fiction story ever written,
Daniel Dennett (1980) proposes a thought experiment:
Imagine a surgical procedure that extirpates your brain
from your head and connects radio transmitters to the
stumps of the nerve cells that carry information from the
brain to the rest of the body and radio receivers tuned to
the same frequency on the complementary segments of
these nerve cells in the body; similarly, this procedure connects
radio transmitters to the stumps of the nerve cells
that carry information from the body to the brain and
appropriately tuned receivers of the sensory nerve cells in
the brain. This is no more than, as one of the characters
in Dennett's story puts it, “stretching the nerves.”[1]
After
the operation, as soon as he is strong enough to be taken
to see his brain, the hero of the story asks himself why he
feels that he is outside the vat looking at his brain, rather
than inside his brain being looked at by his eyes. After all,
he argues, mental events are instantiated in the brain, so
why does he not feel that he is where his mental events
are instantiated? Although we should not take the “results”
of Dennett's thought experiment, however plausible, too
seriously, it is tempting to infer from them that the reason
we feel that we are inside our heads or our bodies is not
because all the important bodily or mental processes occur
inside our body's skin; the experiment suggests that the
spatial location of the machinery that makes mental events possible is irrelevant to our feeling of location. But if the
location of the brain does not determine where we feel
ourselves to be, what does? Perhaps it is the physical
are. Perhaps we feel that we are inside ourselves because
our skin is where the outside ends. This simple answer can
only be part of the truth. For where does our body end
and the world begin? If you are walking in the dark feeling
your way about with a cane, you are unaware of the pressure
of the cane on the palm of your hand; all your attention
is focused on the nature of the obstacles revealed by the
tip of the cane. Under these circumstances, if you had to
classify the cane as part of the world or part of your body,
you would most likely say that it was part of your body.
This is true of all tools. It is also true of vehicles. Most of
the time when you drive an automobile, you are not aware
of your points of contact with the inside of the automobile;
it is as if you had grown a shell around you that you now
inhabit and that your points of contact with the environment
now coincide with the body of the automobile. Thus
it is the external boundaries of your auto body and not the
spaciousness of the car's interior that determine your feeling
of how big a car you are in. In short, the boundary
between the world and ourselves is extremely flexible.
Just how flexible this boundary is becomes clear when
we consider the readiness with which we adopt virtual
viewpoints in a movie theater. When the camera pans (see
Figure 9-1), we feel ourselves turning to scan the environment;
when the camera tilts, we feel ourselves tilting our
heads to look upward or downward; when the camera
engages in a tracking or traveling shot (e.g., when the
camera is set on wheels or tracks), we feel ourselves traveling
forward or backward with the camera. And yet we
know all along that we are sitting in a movie theater.
In fact, as Michael Roemer clearly shows, the use of
virtual points of view can make the difference between an
effective but relatively shallow image and one that endures:
Audiences can be “played” by a skillful movie-maker with a fair
amount of predictability, so that even discriminating audiences
are easily taken in. At the beginning of Bergman's Wild Strawberries
Professor Berg dreams that he is on a deserted street with
all its doors and windows shuttered tight. He looks up at a clock
that has no hands and pulls out his own watch only to find that
his head averted; when he turns, he has no face and his body
dissolves into a pool on the sidewalk. A glass hearse comes down
the street and spills a coffin that opens. Berg approaches and
discovers his own body in the coffin. The corpse comes to life
and tries to pull him in.
The nightmare quality in this sequence is derivative. The deserted,
shuttered street, the clock and watch without hands, the
glass hearse, the faceless man are all conventions familiar to
surrealist painting and literature. Bergman uses them skillfully
and with conviction to produce an effect in the audience, but
they are not true film images, derived from life and rendered in
concrete, physical terms.
There is a similar nightmare in Dreyer's Vampire. A young
man dreams that he has entered a room with an open coffin in
it. He approaches and discovers that he himself is the corpse.
The camera now assumes the point-of-view of the dead man:
we look up at the ceiling. Voices approach and two carpenters
appear in our field of vision. They close the coffin with a lid but
we continue to look out through a small glass window. Talking
indistinctly, they nail down the lid and plane the edges of the
Figure 9-1. Definitions of two elementary
camera movements: pan and
tilt
a candle down on the glass and wax drips onto it. Then the
coffin is lifted up and we pass close under the ceiling, through
the doorway, beneath the sunlit roofs and the church steeple of
a small town — out into the open sky.
Here the detail is concrete: an experience is rendered, not cited;
the situation is objective and out of it emerges, very powerfully,
the feeling that Dreyer is after: a farewell to life, a last confined
look at the earth before the coffin is lowered into the grave.
(1966, pp. 259–60)
According to David N. Lee (Lee and Aronson, 1974;
Lee and Lishman, 1975), the optic array (such as what we
see in a movie theater) contains two sorts of information:
information about the layout of objects in the environment,
which is called exteroceptive[2]
information, and information
about the location of our body and its parts in
the environment, which is called exproprioceptive[3]
information.
Although the exproprioceptive information we
receive is usually consistent, in a movie theater we receive
contradictory exproprioceptive information from two
sources: Our eyes tell us that we are moving with the
camera, while the pressure receptors in our skin tell us that
we are sitting quietly in our seats. Whether we undergo
both experiences at once or whether they alternate we do
not know. It seems that in a movie theater our experiences
are mostly due to the visual input; the visual source that
tells us we are moving overrides the source that tells us
we are sitting.
A similar type of visual dominance can be observed in
the preservation of equilibrium, which is served by the
semicircular canals in our inner ears, the sensors of pressure
in our feet, and the visual sense. Without disturbing the
semicircular canals or moving the feet, it is possible to
cause a standing person to sway and on occasion to fall in
an effort to compensate for the movement of the walls of
a “swinging room” such as depicted in Figure 9-2.
Have someone trace a b or a d on your forehead and try
to identify which of the two letters was traced. You will
Figure 9-2. The moving room of
Lee and Aronson (1974). It had
three vertical sides and a ceiling,
made of polystyrene foam stretched
over a steel frame, but no floor. It
was suspended so that it could swing
noiselessly along an almost perfect
horizontal path.
task, because you weren't told whose point of view to
adopt: the writer's or your own. Now have the person
trace one of these letters on the back of your head. You
will probably not hesitate and report the letter as seen from
behind your head. Now why is there some question regarding
the correct point of view to adopt when a letter
is traced on your forehead and no question regarding which
point of view to adopt when the letter is traced on the
back of your head? After all, if you are “reading” the letter
from within your head, the same ambiguity should arise
when the letter is written on the back of your head: to read
from within looking backward or to read from outside
looking forward. There is one way of making sense of this
dilemma: Suppose we do not mind moving our vantage
things: turning our vantage point backward and “reading”
through the skull. In the case of writing on the forehead,
we cannot avoid doing one of the things we wish to avoid;
in the case of writing on the back of the head, we can
simply move our vantage point behind the head and “read”
the letter from there.
To find out why we resist turning our vantage point
backward compared to our avoidance of reading through
the skull, we must refine our technique somewhat. Instead
of simply asking people to report which letter was traced
on the head, we can assign a vantage point to them and
tell them to adopt one of four vantage points.
Rear vantage point. Wherever a letter is traced on the head,
it should be interpreted from a vantage point behind the
head looking forward. If the letter is traced on the forehead,
it should be read as if the head were transparent and the
letter was written in opaque ink.
Front vantage point. Wherever a letter is traced on the head,
it should be interpreted from a vantage point in front of
the head looking backward. Letters traced on the back of
the head should be read as if the head were transparent.
Internal vantage point. Wherever a letter is traced on the
head, it should be interpreted from a vantage point inside
the head looking radially outward through the transparent
skull. Thus the vantage point faces forward to read a letter
traced on the forehead and backward to read a letter traced
on the back of the head.
External vantage point. Wherever a letter is traced on the
head, it should be interpreted from a vantage point outside
the head looking radially inward at the skull. Thus the
vantage point faces forward to read a letter traced on the
back of the head and backward to read a letter traced on
the forehead.
Now suppose we measured the amount of time it took
to read letters traced on the forehead and on the back of
Figure 9-3. Predictions for speed of
“reading” letters traced on the head
for four assigned vantage points.
Top panel: under assumption that
reading is mostly hindered by turning
vantage point backward. Bottom
panel: under assumption that
reading is mostly hindered by having
to read through skull.
then find out whether the correct interpretation of the traced
letter is slowed down more by having to read through the
skull or by having to turn one's vantage point (see Figure
9-3). To clarify this figure, let us discuss the predictions
for the rear and front vantage points under the two hypotheses.
If of the two obstacles to reading, turning the
vantage point is a greater hindrance than reading through
the skull, then the letters should be read rapidly regardless
of whether they are traced on the forehead or the back of
the head; if, on the other hand, reading through the skull
is the greater obstacle, then letters traced on the back of
the head should be read more quickly than letters traced
on the forehead. Considering now the front vantage point,
if facing backward is a greater hindrance than reading
through the skull, then the letters should be read slowly
wherever they are traced; if, on the other hand, reading
through the skull is the difficulty, then letters traced on
the forehead should be read more quickly than those traced
on the back of the head. Similarly, this reasoning applies
to the remaining two vantage points.
In an experiment begun with Janice Marcus (a graduate
student at Yale) and concluded with David Turock and
Thomas Best (graduate students at Rutgers) (Kubovy et
on the forehead and one position on the back of the
head, there were eight positions, three of which we consider
to be forehead positions and three of which we consider
to be on the back of the head. The results were
unequivocal in their support for our first hypothesis,
namely, that it is harder for us to turn our vantage point
than to read through the skull.
If turning the vantage point is difficult and seeing through
the skull is easy, then there is a hypothesis that can account
for all our data, which we call the disembodied-eye hypothesis.
Suppose that patterns traced on the skin are interpreted as
if they were read by a disembodied eye that has a preferred
position behind the head looking forward. It would take
us too far afield to discuss the pros and cons of this hypothesis;
suffice it to say that, although it has some drawbacks,
this hypothesis has served us well as an aid to thinking
about the perception of patterns traced on the skin and has
not been successfully challenged by any alternative. The
main attraction of the hypothesis in the context of the
present analysis of perspective is that it gives some content
to the idea of projecting one's egocenter to locations in
space outside one's body. Furthermore, the fact that subjects
in our experiments are able to adopt a variety of
vantage points when instructed to do so suggests that the
egocenter (or disembodied eye) is flexible and need not
remain in one position. We are still far from a true understanding
of this fascinating problem of vantage points
in art and in perception in general, but, given the sorts of
evidence we now have, the notion of a movable egocenter
cannot be treated any more as a frivolous fancy.
We have reached the point where the fifth purpose of
perspective, mentioned in the introduction, can be summarized.
I claim that, for viewers familiar with perspective,
powerful effects can be achieved by creating discrepancies
between the natural direction of the viewer's line of sight
and the line of sight implicit in the perspective of the painting
(as was the case with Mantegna's Saint James Led to
Execution, Figure 8-7), or by locating the center of projection
high above the viewer's eye level (as in Leonardo's
divorcing the viewer's felt point of view in relation to the
scene represented in the painting from the viewer's felt
position in relation to the room in which he or she is
standing. We cannot do more, in our present state of
knowledge, than to speculate on the effect of such discrepancies,
which I believe induce a feeling of spirituality,
perhaps one conducive to a religious experience: a separation
of the mind's eye from the bodily eye. Such effects
were very much in accord with the aims of the Renaissance
painters, who wished to convey a religious experience
through their art. For, as Paul Oskar Kristeller points out
in his discussion of paganism and Christianity in Renaissance
thought,
if an age where the nonreligious concerns that had been growing
for centuries attained a kind of equilibrium with religious and
theological thought, or even began to surpass it in vitality and
appeal, must be called pagan, the Renaissance was pagan, at least
in certain places and phases. Yet since the religious convictions
of Christianity were either retained or transformed, but never
really challenged, it seems more appropriate to call the Renaissance
a fundamentally Christian age. (1961, p. 73)
Furthermore, the divorce of the mind's eye from the bodily
eye is very much in the spirit of Renaissance Platonism.
Plato's thought and Neoplatonism, which had been eclipsed
during medieval times, were revived by Marsilio Ficino
(see Introduction). Kristeller writes as follows about Ficino's
theory of contemplation:
In the face of ordinary daily experiences, the mind finds itself in
a state of continuous unrest and dissatisfaction, but it is capable
of turning away from the body and the external world and of
concentrating upon its own inner substance. (1967, p. 198)
Now I do not mean to equate Ficino's concept of contemplation
with the use of perspective to separate the mind's
eye from the bodily eye. Nevertheless, I do wish to suggest
that such a use of perspective is in keeping with the spiritual
concerns of intellectuals in the late fifteenth and early sixteenth
centuries.
The lack of contemporary analyses of this issue is perhaps
Figure 9-4. The Parthenon, from
northwest (447–432 B.C.)
Figure 9-5. Diagram in exaggerated
proportion of horizontal curvature of
Parthenon
little was written about perspective in general during the
fifteenth and early sixteenth centuries, one's surprise wanes
somewhat. Furthermore, when we look back at the ground
we have covered up to this point in this book, it becomes
apparent that our understanding of optics, geometry, and
perception is far more advanced than it was half a millennium
ago. It is not surprising, therefore, that Renaissance
artists had to proceed more by intuition and rule of thumb
than by analysis and deduction; whatever discoveries they
made were most likely in the form of tacit knowledge,
which is notoriously difficult to understand and analyze.
Furthermore, this is not the only time in the history of art
that subtle and complex procedures were developed to
achieve perceptual and spiritual effects, for which little or
no documentary evidence remains, the Parthenon (see Figure
9-4) being a prime example. Just as the Renaissance
artists deviated from the geometric dictates of perspective,
the Parthenon deviates from mathematical regularity in
several ways. One of these is illustrated in Figure 9-5. To
this very day, several theories concerning the purpose of
these so-called refinements compete for the favor of scholars
(Carpenter, 1970; Pollitt, 1972).
There is, to be sure, considerably more involved in performing such a
technological feat, such as ensuring that the blood that flows through
the extirpated brain has exactly the same composition as the blood
coursing through the brainless body, because otherwise you could never
get drunk, suffer from premenstrual tension, or become sexually aroused.
| 9 The psychology of egocenters The psychology of perspective and Renaissance art | |