less extensive than the heavy soreness of a boil or the vast
discomfort of a colic or a lumbago; and a solitary star
looks smaller than the noonday sky. Muscular sensations
and semicircular-canal sensations have volume. Smells
and tiwtes are not without it; and sensations from our
inwjird organs have it in a marked degree.
Iifpletion and em])tinesH, sulTocation, pal])itation, head-
ache, are examples of this, and certainly not less spatial is
the cousciousnesa we have oT <mr general bodily condition
336 PSYCHOLOGY.
in nausea, fever, heavy drowsiness, and fatigue. Our entire
cubic content seems then sensibly manifest to us as such,
and feels much larger than any local pulsation, pressure,
or discomfort. KSkin and retina are, however, the organs
in which the s])ace-element plays the most active part.
Not only does the maximal vastness yielded by the retina
surpass that yielded by any other organ, but the intricacy
with which our attention can subdivide this vastness and
perceive it to be composed of lesser portions simultaneously
coexisting alongside of each other is without a parallel
elsewhere. The ear gives a greater vastness than the skin,
but is considerably less able to subdivide it. The vastness,
moreove)', is as great in one direction as in anotlier. Its
dimensions are so vague that in it there is no question as
yet of surface as opposed to depth; 'volume^ being the
best short name for the sensation in question.
Sensations of different orders are roughly comparable
ivith each other as to their volumes. Persons born blind
are said to be surprised at the largeness with which objects
appear to them when their sight is restored. Franz says
of his patient cured of cataract: "He saw everything much
larger than he had supposed from the idea obtained by his
sense of touch. Moving, and especially living, objects ap-
peared very large.'' Loud sounds have a certain enormous-
ness of feeling. * Glowing ' bodies as Hering says, give us a
perception "which seems roomy {raumhaft) in comparison
with that of strictly surface-color. A glowing iron looks
luminous through and through, and so does a flame." The
interior of one's mouth-cavity feels larger when explored
by the tongue than when looked at. The crater of a
newly-extracted tooth, and the movements of a loose tooth
in its socket, feel quite monstrous. A midge buzzing
against the drum of the ear will often seem as big as a
butterfly. The pressure of the air in the tympanic cavity
upom the membrane gives an astonishingly large sensation.
Tlie voluminousness of the feeling seems to bear very little
relation to the size of the nrqan that yields it. The ear and
THE PERCEPTION OF SPACE. 337
eye are comparatively niiiinte organs, yet they give us feel-
ings of great volume. The same lack of exact proportion
between size of feeling and size of organ affected obtains
witliin the limits of particular sensory organs. An object
appears smaller ou the lateral portions of the retina than
it does on the fovea, as may be easily verified by holding
the two forefingers parallel and a couple of inches apart,
and transferring the gaze of one eye from one to the
other. Then the finger not directly looked at will appear
to shrink. On the skin, if two points kept equidistant
(blunted compass- or scissors-points, for example) be drawn
along so as really to describe a pair of parallel lines, the
lines will appear farther apart in some spots than in
others. If, for example, we draw them across the face, the
person experimented upon will feel as if they began to
diverge near the mouth and to include it iu a well-marked
ellipse.
Fia. C5 (after VVeberX
The dotted lines give the real course of the points, the continuous lines the
Course as felt.
Now MY FIRST THESIS IS THAT THIS EXTENSiTY, dis-
cernible in each and every sensation, though more developed
in some than in others, is the ohkjixal sensation of
SPACE, out of which all the exact knowledge al)out space
that we afterwards come to have is woven Ijy ])rocesse8 of
discrimination, association, and selection.
The Construction of Real Space. — To the babe who first
opens his senses upon the world, though the experience is
one of vastnesB or extensity, it is of an extensity within
338 PSTCHOLOOT.
which no definite divisions, directions, sizes, or distances
are yet marked out. Potentially, the room in which the
child is born is subdivisible into a multitude of parts,
fixed or movable, which at any given moment of time have
definite relations to each other and to his person. Poten
tially, too, this room taken as a whole can be prolonged ii
various directions by the addition to it of those farther
lying spaces which constitute the outer world. But actii
ally the further spaces are unfelt, and the subdivisions ar»
undiscriminated, by the babe; the chief part of whose edu
cation during his first year of life consists in his becoming
acquainted with them and recognizing and identifying
them in detail. This process may be called that of the con
sfruction of real space, as a newly apprehended object, out
of the original chaotic experiences of vastness. It consists
of several subordinate processes :
First, the total object of vision or of feeling at any tiiiie
7nust have smaller objects definitely disci'iminated loitlim
it;
Secondly, objects seen or tasted must be identified with
objects felt, heard, etc., and vice versa, so that the same
'thing' may come to be recognized, although apprehended
in such widely differing ways;
Third, the total extent felt at any time must be con-
ceived as definitely located in the midst of the surrounding
extents of 2ohich the world consists;
Fourth, these objects mast appear arranged in definitb
order in the so-called three dimensions; and
Fifth, their relative sizes must be perceived — in othei
words, they must be measured.
Let us take these processes in regular order.
1) Subdivision or Discrimination. — Concerning this
there is not much to be added to what was set forth in
Chapter XV. Moving parts, sharp parts, brightly colored
parts of the total field of perception ' catch the attention '
and are then discerned as special objects surrounded by
the remainder of the field of view or touch. That when
THE PERCEPTION OF SPACE. 339
such objects are discerned apart they should appear as
thus surrounded, must be set down as an ultimate fact of
our sensibility of which no farther account can be given.
Later, as one partial object of tliis sort after another has
become familiar and identifiable, the attention can be
caught bv more than one at once. We then see or feel a
number of distinct objects alongside of each other in the
general extended field. The ' alongsideness ' is in the first
instance vaijue — it mav not carry with it the sense of dofi-
uite directions or distances — and it too must be regarded
a£ an ultimate fact of our sensibility.
•J) Coalescence of Different Sensations into the Same
'Thing.' — \\'iieu two senses are impressed simultrjieously
we tend to identify their objects as nne tiling. AVhen a
conductor is brought near the skin, the snap heard, the
spark seen, aiul the sting felt, are all located together and
believed to be different aspects of one entity, the 'electric
discharge.' The space of the seen object fuses with the
space of the heard object and with that of the felt object
by an ultimate law of our consciousness, which is that we
simplify, unify, and identify as much as we possibly can.
]Miatevcr sensible data can be attended to together we locate
together. Their several extents seem one extent. The place
at which each appears is held to be the same with the place
at which the others appear. This is the first and great
*act' by which our world gets spatially arranged.
In this coalescence in a 'thing,' one of the coalescing
sensations is held to /je the thing, the other sensations are
taken for its more or less accidental properties, or modes
of apj)earancc. The sensation chosen to be essentially the
thing is the most constant and practically important of the
lot ; most often it is hardness or weight. Hut the hardness
or weight is never without tactile^ ])iilk; and as wo can
always see something in our hand when we feel souu'thing
there, we equate the bulk felt with the bulk seen, and
thenceforward this common hulk is also apt to figure as
of the essence of the ' thing.' Frequently a shape so fig-
340 PSYCHOLOOr.
ures, sometimes a temperature, a taste, etc.; but for the
most part temperature, smell, sound, color, or whatever
other phenomena may vividly impress us simultaneously
with the bulk felt or seen, figure among the accidents.
Smell and sound impress us, it is true, when we neither
see nor touch the thing; but they are strongest when we
see or touch, so we locate the source of these properties
within the touched or seen space, whilst the properties
themselves we regard as overflowing in a weakened form
into the spaces filled by other things. In all this, it will
be observed, the sense-data whose spaces coalesce into one are
yielded hy different sense-organs. Such data have no ten-
dency to displace each other from consciousness, but can
be attended to together all at once. Often indeed they
vary concomitantly and reach a maximum together. We
may be sure, therefore, that the general rule of our mind
is to locate in each other all sensations which are asso-
ciated in simultaneous experience and do not interfere
with each other's perception.
3) The Sense of the Surrounding World. — Differefit im-
pressions on the same sense-organ do interfere with each
other's perception and cannot well be attended to at once.
Hence we do not locale them in each other's spaces, but
arrange them in a serial order of exteriority, each alongside
of the rest, ill a space larger than that lohich any one sensa-
tion brings. We can usually recover anything lost from
our sight by moving our eyes back in its direction; and
it is through these constant changes that every field of
seen things comes at last to be thought of as always hav-
ing a fringe of other things possible to be seen spreading
in all directions round about it. Meanwhile the move-
ments concomitantly with which the various fields alter-
nate are also felt and remembered; and gradually (through
association) this and that movement come in our thought
to suggest this or that extent of fresh objects introduced.
Gradually, too, since the objects vary indefinitely in kind,
we abstract from their several natures and think separately
THE PERCEPTION OF SPACE. 841
of their mere extents, of wliich extents the various move-
ments n-main as the only constant introducers and asso-
ciates. More and more, therefore, do we tliink of move-
ment and seen extent as mutually ijivolving each other,
until at last we may get to regard them as synonymous;
and, empty s])ace then meaning for us mere room for move-
im-nf, we may, if we are psychologists, readily hut errone-
ously assign to the ' muscular sense ' the chief role in
perceiving extensiveness at all.
4) The Serial Order of Locations. — The muscular sense
has much to do with defining the order of position of things
seen, felt, or heard. We look at a point; another point
upon the retina's margin catches our attention, and in an
instant we turn the fovea upon it, letting its image suc-
cessively fall upon all the points of the intervening retinal
line. The line thus traced so rapidly hy the second point
is itself a visual ohject, with the first and second point at
its respective ends. It separates the points, which become
located Inj its length with reference to each other. If a
third point catch the attention, more peripheral still than
the second point, then a still greater movement of the eye-
ball and a continuation of the line will result, the second
point now a})pearing between the first and third. Every
moment of our life, peripherally-lying objects are drawing
lines like this between themselves and other objects which
tliey dis])lace from our attention as we bring tliem to the
centre of our field of view. Each peripheral retiiud point
comes in this way to suggest a line at the end of which it
lies, a line which a possible movement will trace; and even
the motionless field of vision ends at last by signifying
a system of positions brought out by possible movements
between its centre and all periiiheral pai't.s.
It is the same with oxw skin and joints. By moving our
hand over objects we trace lines of direction, ami new im-
jiressions arise at their ends. The ' lines ' are sometimes on
the articular surfaces, sometimes on the skin as well; in
either case they give a definite order of arrangement to the
342 PSTCnOLOOY.
successive objects between which they intervene. Similarly
with sounds and smells. With our heads in a certain posi-
tion, a certain sound or a certain smell is most distinct.
Turning our head makes this experience fainter and brings
another sound, or another smell, to its maximum. The two
sounds or smells are thus separated by the movement located
at its ends, the movement itself being realized as a sweep
through space whose value is given partly by the semi-
circular-canal feeling, partly by the articular cartilages of
the neck, and partly by the impressions produced upon the
eye.
By such general principles of action as these everything
looked at, felt, smelt, or heard comes to be located in a
more or less definite position relatively to other collateral
things either actually presented or only imagined as possi-
bly there. I say 'collateral' things, for I prefer not to
complicate the account just yet with any special considera-
tion of the * third dimension/ distance, or depth, as it has
been called.
5) The Measurement of Things in Terms of Each Other.—
Here the first thing that seems evident is that we have no
i7nmediafe power of comparing together with any accuracy
the extents revealed by different sensations. Our mouth-
cavity feels indeed to the tongue larger than it feels to the
finger or eye, our lips feel larger than a surface equal to
them on our thigh. So much comparison is immediate;
but it is vague; and for anything exact we must resort to
other help.
The great agent in comparing the extent felt hy one sen-
sory surface luith that felt hy another is superposition-
superposition of one surface upon another, and superposi-
tion of one outer thing upon many surfaces.
Two surfaces of skin superposed on each other are felt
simultaneously, and by the law laid down on p. 339 are
judged to occupy an identical place. Similarly of our
hand, when seen and felt at the same time by its resident
sensibility.
THIS rKHCErnuN of sfaue. 343
In these identifications and reductions of the many to the
one it must be noticed tluit when the resident sensations of
largeness of two opposed surfaces conflict, one of the sensa-
tions is chosen as the true standard and the other treated as
ill u sort/. Thus an empty tooth-socket is believed to be really
smaller than the finger-tip which it will not admit, al-
though it may feel larger; and in general it maybe said
that the hand, as the almost exclusive organ of palpation,
gives its own magnitude to the other parts, instead of hav-
ing its size determined by them.
Hut even though exploration of one surface by another
were impossible, jve could always measure our various sur-
faces against each other by applying the same extended
object first to one and then in another. "We might of course
at first suppose that the object itself waxed and waned as
it glided from one place to another (cf. above. Fig. 65); but
the principle of simplifying as much as possil)le our world
would soon drive us out of that assumption into the easier
one that objects as a rule keep their sizes, and that most of
our sensations are affected by errors for which a constant
allowance must be made.
In the retina there is no reason to suppose that the
bignesses of two impressions (lines or blotches) falling on
different regions are at first felt to stand in any exact
mutual ratio. But if the impressions come froni the same
object, then we might judge their sizes to be just the same.
1'liis, however, only when the relation of the o])ject to the
eye is believed to be on the whole unchanged. AVhen the
object, by moving, changes its relations to the eye, the sen-
sation excited by its image even on the same retinal region
becomes so fluctuating that we end l)y ascribing no abso-
lute import whatever to the retinal space-feeling which at
any moment we may rei;eive. So complete does this over-
looking of retinal magnitude become that it is next to
impossible to compare the visual magnitudes of oljjects at
different distances without making the experiment of
superposition. We cannot say beforehand how much of u
344 PSYCHOLOGY.
distant house or tree our finger will cover. The various
answers to the familiar question. How large is the moon ?
— answers which vary from a cartwheel to a wafer — illus-
trate this most strikingly. The hardest part of the train-
ing of a young draughtsman is his learning to feel directly
the retinal (i.e. primitively sensible) magnitudes which the
different objects in the field of view subtend. To do this
he must recover what Ruskin calls the ' innocence of the
eye ' — that is, a sort of childish perception of stains of
color merely as such, without consciousness of what they
mean.
With the rest of us this innocence is lost. Out of all the
visual magnikides of each l-nown object we have selected
one as the 'real' one to think of, and degraded all the
others to serve as its signs. This real magnitude is deter-
mined by aesthetic and practical interests. It is that which
we get when the object is at the distance most propitious
for exact visual discrimination of its details. This is the
distance at which we hold anything we are examining.
Farther than this we see it too small, nearer too large. And
the larger and the smaller feeling vanish in the act of sug-
gesting this one, their more important meaning. As I look
along the dining-table I overlook the fact that the farther
plates and glasses /ee? so much smaller than my own, for I
knoio that they are all equal in size; and the feeling of
them, which is a present sensation, is eclipsed in the glare
of the knowledge, which is a merely imagined one.
It is the same with shape as ivith size. Almost all the
visible shapes of tbings are what we call perspective ' dis-
tortions.' Square table -tops constantly present two acute
and two obtuse angles; circles drawn on our wall-papers,
our carpets, or on sheets of paper, usually show like ellipses;
parallels approach as they recede; human bodies are fore-
shortened ; and the transitions from one to another of these
altering forms are infinite and continual. Out of the flux,
however, one phase always stands prominent. It is the
form the object has when we see it easiest and best : and
THE PERCEPTION OF SPACE. 345
that is when our eyes and the object both are in wliat may
be called the normal position. In tliis position our head is
upriHit and our optic axes either parallel or synunetrically
convergent; the plane of the object is perpendicular to the
visual plane; and if the object is one containing many
lines, it is turned so as to make them, as far as possible^
either parallel or perpendicular to the visual plane. In this
situation it is that we compare all shapes with each other;
here every exact measurement and every decision is made.
Most sensations are signs to us of other sensations whose
space- value is held to be more real. Tlie tiling as it would
appear to the eye if it were in the normal jmsition is what
we thini- of whenever we get one of the other optical views.
Only as represented in the normal position do we believe
we see the object as it is ; elsewhere, only as it seems.
Experience and custom soon teach us, however, that the
seeming appearance passes into the real one by continuous
gradations. They teach us, moreover, that seeming and
being may be strangely interchanged. Now a real circle
may slide into a seeming ellipse; now an ellipse may, by
sliding in the same direction, become a seeming circle;
now a rectangular cross grows slant-legged; now a slant-
legged one grows rectangular.
Almost any form in oblique vision maybe thus a deriva-
tive of almost any other in 'primary' vision; and we must
learn, when we get one of th.e former appearances, to trans-
late it into the appropriate one of the latter class; we must
learn of what optical ' reality ' it is one of the optical signs.
Having learned this, we do but obey that law of economy
or simplification which dominates our whole psychic life,
when wo think exclusively of the 'reality' and ignore ns
much as f)ur consciousness will let us the 'sign' by which
we came to apprehend it. The signs of each probable real
thing being multiple and the thing itself one and fixed,
we gain the same mental relief by abandoning the former
for the latter that we do when we abandon mental images,
â– with all their fluctuating characters, for the definite and
346 PSYCHOLOGY.
unchangeable names which they suggest. The selection of
the several 'normal' appearances from out of the jungle
of our optical experiences, to serve as the real sights of
which we shall think, has thus some analogy to the habit of
thinking in words, in that by both we substitute terms few
and fixed for terms manifold and vague.
If an optical sensation can thus be a mere sign to recall
another sensation of the same sense, judged more real, a
foriiori can sensations of one sense be signs of realities
which are objects of another. Smells and tastes make ua
believe the visible cologne-bottle, strawberry, or cheese to
be there. Sights suggest objects of touch, touches suggest
objects of sight, etc. In all this substitution and sugges-
tive recall the only law that holds good is that in general
the most interesting of the sensations which the ' thing '
can give us is held to represent its real nature most truly.
It is a case of the selective activity mentioned on p. 170 ff.
The Third Dimension or Distance. — This service of sensa-
tions as mere signs, to be ignored when they have evoked
the other sensations which are their significates, was
noticed first by Berkeley in his new theory of vision. He
dwelt particularly on the fact that the signs were not
natural signs, but properties of the object merely associ-
ated by experience with the more real aspects of it which
they recall. The tangible ' feel ' of a thing, and the * look '
of it to the eye, have absolutely no point in common, said
Berkeley; and if I think of the look of it when I get the
feel, or think of the feel when I get the look, that is merely
due to the fact that I have on so many previous occasions
had the two sensations at once. AVhen we open our eyes,
for example, we think we see how far off the object is.
But this feeling of distance, according to Berkeley, cannot
possibly be a retinal sensation, for a point in outer space
can only impress our retina by the single dot which it
projects ' in the fund of the eye,' and this dot is the same
for all distances. Distance from the eye, Berkeley con-
sidered not to be an optical object at all, but an object of
THE PERCEPTION OF SPACE. 347
foucliy of wliioh wo have optical signs of various sorts, such
as tlie image's ai)i)arent magnitude, its 'faiutuess' or 'con-
fusion,' and the 'strain' of accommodation aiul convert
gence. By distance being an object of 'touch,' Herkeh\v
meant that our notion of it consists in ideas of the amount
of nuiscular movement of arm or h^gs whicli v>oukl be
required to place our hand upon the object. Most authors
have agreed witli Berkeley that creatures unalde to move
either their eyes or limbs would have no notion whatever
of distance or the third dimension.
Tliis opinion seems to me unjustifiable. I cannot get
over the fact that all our sensations are of volume, {\.w^ that
the primitive field of view (however imperfectly distance
may be discriminated or measured in it) cannot be of
something flat, as these authors unanimously maintain.
Nor can I get over the fact that distance, when I see it, is
a genuinely optical feeling, even though I be at a loss to
assign any one physiological process in the organ of vision
to the varying degrees of which the variations of the feeh
ing uniformly correspond. It is awakened by all the op^
tical signs whicli Berkeley mentioned, and by more besides,
such as Whcatstone's binocular disparity, and by the par-