The moving self and the unmoving world are reciprocal aspects of the same perception. To say that one perceives an outflow of the world ahead and an inflow of the world behind as one moves forward in the environment would be quite false.

1. THE AMBIENT OPTIC /Haptic
ARRAY Part Two

2. The point of observation
• The point of observation for an ambient optic array is not
occupied.
• The point has been thought of as a position at which observation
could be made, a position that could be occupied but need not
be.
• It was important to establish this principle that the point of
observation is public, not private, but now we must consider the
other side of the coin.
• When a point of observation is occupied, there is also optical
information to specify the observer himself, and this information
cannot be shared by other observers.
• For the body of the animal who is observing temporarily conceals
some portion of the environment in a way that is unique to that
animal.
• I call this information propriospecific as distinguished from
extrospecific, meaning that it specifies the self as distinguished
from the environment.

3. THE SPECIFYING OF THE SELF
BY THE FIELD OF VIEW
• The field of view of an animal is the solid
angle of the ambient light that can be
registered by its ocular system. The field of
view, unlike the ambient array, is bounded;
it is a sort of sample of the whole sphere.
• The angular scope of the field of view
depends on the placement of the eyes in
the head, some animals having lateral eyes
and a nearly panoramic field of view and
others having frontal eyes and a roughly
hemispherical field of view.

4. The lateral eyes of a horse and
the frontal eyes of a man and the
respective fields of view

5. Visual solid angle

6. The ego as seen by the left eye.
The temporary field of view of the
left orbit of an observer.

7. • The drawing is an updating of one made by
Ernst Mach in the 1880s that he entitled
"The Visual Ego."
• What is being illustrated here is the
stationary field of view of an eye socket
with the head fixed and the eye mobile, not
the shifting field of view with a fixed eye
and a turning head; the latter is different
and will be described later.
• For this drawing, the artist had to turn his
eye in order to see clearly the peripheral
details in the field of view.

8. Projected and Unprojected
Surfaces in a Stationary Optic
Array

9. Optical Occlusion and Edge-
Information in an Optic Array

10. A field of view
• A field of view is a large visual solid angle, with an
envelope.
• The important fact about a field of view is its
boundaries, vague and indefinite boundaries, to be
sure, but still boundaries.
• They are in some ways like occluding edges, the
occluding edges of window.
• The edges of the field of view hide the environment
behind them, as those of a window do, and when the
field moves there is an accretion of optical structure at
the leading edge with deletion of structure at the
trailing edge.
• Ask yourself what it is that you see hiding the
surroundings as you look out upon the world-not
darkness surely, not air, not nothing, but the ego’.

11. A point of observation is occupied
by a human
• Whenever a point of observation is occupied by a human,
about half of the surrounding world is revealed to the eyes
and the remainder is concealed by the head.
• What is concealed is occluded not by a surface, a projected
surface of the sort described when the laws of occluding
and occluded surfaces were formulated, but by a unique
entity.
• It is not a part of the world, but it does conform to the
principle of reversible occlusion, by which those surfaces
that go out of sight with one movement come back into
sight with the opposite movement.
• The head turns, and whatever was in back of the head at
one time will be in front of the head at another and vice
versa.
• This fact is fundamental for the theory of perception to be
proposed.

12. The experience of a central self in the
head and a peripheral self in the body
• Still other occluding edges appear within it, those of the nose, the
body, the limbs, and the extremities, some of which can be seen
in the drawing. The edges of the eye socket, the eyebrows, the
nose and cheek bones are only the nearest;
• the edges of the arms, legs, hands, and feet are more distant, but
they still occlude the surfaces of the "outer" environment. The
hands and feet behave more like the occluding edges of an
object than like the occluding edges of a window; they are
actually protrusions into the field of view from below.
• When these semi objects move, there is deletion of optical
structure at the leading edge and accretion at the trailing edge,
just as with objects in the world.
• Information exists in a normal ambient array, therefore, to specify
the nearness of the parts of the self to the point of observation-
first the head, then the body, the limbs, and the extremities.

13. Deletion of optical structure at the
leading edge and accretion at the
trailing edge

14. NONVISUAL INFORMATION
ABOUT THE SELF
• The observer's movements usually produce sights and
sounds and impressions on the skin along with stimulation
of the muscles, the joints, and the inner ear. Accordingly,
information that is specific to the self is picked up as such,
no matter what sensory nerve is delivering impulses to the
brain.
• The point is that information about the self is multiple and
that all kinds are picked up concurrently.
• An individual not only sees himself, he hears his footsteps
and his voice, he touches the floor and his tools, and when
he touches his own skin he feels both his hand and his skin
at the same time.
• He feels his head turning, his muscles flexing, and his joints
bending. He has his own aches, the pressures of his own
clothing, the look of his own eyeglasses-in fact. he lives
within his own skin.

15. EGORECEPTION AND
EXTEROCEPTION
ARE INSEPARABLE• The optical information to specify the self, including the
head, body, arms, and hands, accompanies the optical
information to specify the environment. The two sources of
information coexist.
• When a man sees the world, he sees his nose at the same
time; or rather, the world and his nose are both specified
and his awareness can shift. which of the two he notices
depends on his attitude; what needs emphasis now is that
information is available for both.
• The supposedly separate realms of the subjective and the
objective are actually only poles of attention. The dualism
of observer and environment is unnecessary. The
information for the perception of "here" is of the same kind
as the information for the perception of "there," and a
continuous layout of surfaces extends from one to the other.
• Self-perception and environment perception go together.

16. The Specifying of Head turning
• The head can be turned as well as displaced. Turning
the bead is looking around; displacing it is locomotion.
• They are specified by what I have called the sweeping
of the field of view over the ambient array during
head turns and the wheeling of the field over the array
during head tilts.
• The sweeping and wheeling of this window with its
special private occluding edges are not simply
"motions" but deletions and accretions of optical
structure.
• To say only that the field of view "moves" over the
world as the head moves is inexact and insufficient;
the world is revealed and concealed as the head
moves, in ways that specify exactly how the head
moves.

17. A sequence of overlapping fields
of view obtained by turning the
head to the right.

18. His feet are now lined up with the window instead of
with the corner of the room. The head turns through an
angle of about 90". His nose is always at the right-hand
edge of the field. The field of view is a sliding sample of
the ambient array.

19. The optical texture that is deleted
is subsequently accreted
• Binocular disparity refers to the difference in image
location of an object seen by the left and right eyes
• The combined field of view of two eye sockets (and
all higher animals have two eyes) consists of two
samples of the ambient array.
• They overlap more or less, more in humans than in
horses, and thus the same structure is included in
both segments.
• But it is not quite the same structure, because the
two points of observation are slightly separated and
there is a resulting disparity of the two structures.

20. This disparity, or
mismatch, is at a maximum
• The edge of the nose is the left-hand edge
of what the right eye sees but the right-
hand edge of what the left eye sees, and
this maximum mismatch constitutes
information for the zero of distance, that is,
for the awareness of oneself at the center
of a layout of surfaces receding from here.
• The minimum of mismatch is at the horizon.

21. THE SPECIFYING OF LIMB
MOVEMENTS
• Consider in more detail the protrusions into
the field of view of those complex shapes
with deforming outlines that are the
projections of the limbs and extremities of
the observer's body.
• They normally enter and leave the field at
its lower edge, or else the field sweeps
down to reveal them. They are almost never
at rest.
• They specify objects in some ways, but of
course they are only semi objects.

22. Subjective objects
• This paradox would emphasize the fact that no line can be
drawn between the subjective and the objective.
• In the primate and the human, the five pronged shapes
that specify the hands are especially meaningful. Their
deforming contours and the underlying invariants make
possible what psychologists have called, very inadequately,
eye-hand coordination.
• More exactly, they are the basis of the visual control of
manipulation. And when an object grasped by the hand is
used as a tool, it becomes a sort of extension of the hand,
almost a part of the body.
• Infants, both monkey and human, practice looking at their
hands for hours, as well they should, for the disturbances of
optical structure that specify the niceties of apprehension
have to be distinguished.

23. The optical minification and
magnification
• The optical minification of the squirming silhouette of the
hand specifies extension of the arm, reaching out, while
optical magnification specifies flection of the arm, pulling in.
• A hand occludes progressively less of the environment as it
recedes and progressively more of the environment as it
approaches. A certain nonsymmetrical magnification of the
hand will bring it to the mouth, as every baby learns.
• A symmetrical magnification of the hand will cause it to
cover the eyes so that nothing can be seen.
• The visual solid angle of the hand cannot be reduced below
a certain minimum; the visual solid angle of a detached
object like a ball can be made very small by throwing it.
• These ranges of magnification and minification between
limits link up the squirming silhouette extremes of here and
out there, the body and the world, and constitute another
bridge between the subjective and the objective.

24. Contact of the hand or foot with a
surface
• You might think that contact of the hand or foot with a surface
during extension of the limb is specified by a mechanical
impression on the skin, by touch, and that there would be no use
for an optical specification as well.
• Nevertheless, there is such optical specification. When the
decreasing occlusion of the surface by the extremity ceases, and
when there is no accretion or deletion of surface texture by the
occluding edges of the hand or foot, then the extremity is in
contact with the surface and not sliding over it. This specifies, for
example, that the foot is on the ground.
• Terrestrial animals are accustomed to have their feet on the
ground and to have both cutaneous and optical information for
this state of affairs.
• This explains why an invisible glass floor high above the real floor
supplies mechanical support but not optical support, and why it
is that human infants and other terrestrial animals show distress,
flinching and behaving as if falling, when placed on such a
transparent floor.

25. THE SPECIFYING OF
LOCOMOTION
• Locomotion is specified by flow of the array
and rest by non flow. The flow is a change
in perspective structure, a change in the
perspectives of the ground if outdoors and
of the floor, walls, and ceiling if indoors.
• There is not only a static perspective of the
array but also a motion perspective.
• The main law of flowing perspective is that
it is centrifugal in half the array and
centripetal in the other half, but these two
hemispheres are not invariant.

26. The two foci of inflow and outflow
• More particularly, a focus of centrifugal outflow is
always accompanied by another focus of centripetal
inflow at the opposite pole of the sphere.
• This axis is the line of the displacement of the
observer. Hence, the focus of expansion is the
direction in which one is going, and the focus of
contraction is the direction from which one is
coming.
• This direction may change during locomotion, of
course, relative to the permanent environment of
earth and sky, and the two foci of inflow and
outflow may change correspondingly relative to
other invariants of the ambient array.

27. The flow pattern
• The invariant structure of the array that specifies the
persisting world underlies the changing perspective
structure. The pattern of outflow and inflow is
superposed, as it were, on the nonchanging features
of the array.
• One of these nonchanging features is the earth-sky
contrast at the horizon, and another is the texture of
the earth. The flow pattern shifts as the observer
changes direction, now in one direction and then
another, and reverses when the direction is reversed,
but the invariants of structure and texture never shift.
• They specify the unmoving terrain, whereas the Flow
pattern specifies the observer's locomotion with
reference to the terrain.

28. How do we see where we are
going?
• We guide or steer our locomotion, when we are
in control of it, by locating those invariant
features of the array that specify a destination,
whatever it may be, and then keeping the focus
of optical outflow centered on that item. In short,
we magnify the form that specifies the goal.
• A child runs to his mother by enlarging her
image to the limit, that is, to the largest possible
solid angle;
• a bee flies to a flower by precisely the same rule.
The rule is related to the principle of what I have
called the '"symmetricalizing'" of stimulation.

29. The moving self and the
unmoving world
• The centrifugal outflow of the array that specifies locomotion
does not interfere with the information that specifies surface
layout; the invariants are all the better for the transformation.
• The moving self and the unmoving world are reciprocal aspects
of the same perception. To say that one perceives an outflow of
the world ahead and an inflow of the world behind as one moves
forward in the environment would be quite false.
• One experiences a rigid world and a flowing array.
• The optical flow of the ambient array is almost never perceived as
motion; it is simply experienced as kinesthesis, that is
egolocomotion (Warren, 1976).
• Consider, finally, an environment with hidden surfaces. An open
environment projects a continuous flow pattern to the eye of a
moving observer, but a cluttered environment does not.
• This kind of change is not a flow or a transformation, because the
units of the array, some of them, do not map from preceding to
succeeding arrays. The invariants that specify the layout of the
real environment, then, are not simply invariants under projective
transformations.

30. The flow of the optic array during
locomotion parallel to the ground.

31. The outflow of the optic array
from the focus of expansion on
the horizon.

32. The flow of the optic array to the
right of the direction of
locomotion.

33. The outflow of the optic array in a landing glide.
This is what the flier would see if he aimed down
at the landing field.

34. How is this optical How related to
classical kinesthesis?
• Kinesthesis, which is supposed to be the sense of movement.
• A person who walks or runs or rides a bicycle does get sensations
from the muscles and joints that specify movement. All I propose
is that visual kinesthesis should be recognized along with muscle-
joint kinesthesis.
• The latter does not function during passive locomotion in a
vehicle. Visual kinesthesis yields the only reliable information
about displacement. The classical sense of movement is not
trustworthy, for a fish in a stream and a bird in a wind have to
exercise their muscles and joints strenuously merely to stay in the
same place.
• The animal is moving in one meaning but not in another.
Locomotion with respect to the earth, active or passive, is
registered by vision, but supplementary information about the
movement of a limb relative to the body is picked up by the
haptic system (Gibson, 1966b, Ch. 4).