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soon becomes tolerably accurate.

Permanent existence of Material Objects. — The several
members and parts of his own body permanently present
as the centre of his pleasures and pains, and the subject
of his sensations of double contact, are known to be
very different from all other objects. These latter by
their repeated recurrence to his notice in like circum-
stances, by the frequently confirmed experience that he
can renew his acquaintance with them at will, and by
their regularity in producing their effects, whether
observed or unobserved, first evoke a dim belief, and
then a rational conviction as to their abiding existence
when beyond his view. Consequently, at a very early
stage in his existence he becomes alive to the fact that
his nurse, his bed, his food, and other objects of interest
are not annihilated every time he closes his eyes.

Inferential knowledge of othey Minds. — Among external
objects a class particularly interesting for the child are


organisms like in shape to his own, These bodies,
moreover, react by movement in response to stimuli
just as he himself does. But in his own case his
consciousness assures him that mental states are the
effects of similar stimulation and the causes of similar
movements. Consequently, by analogy he infers that
mental existences like his own are present in other human
bodies. Language is indeed the strongest evidence for
the reality of other human minds, but even when it is
absent, as in the case of the lower animals, the
argument is felt to be irresistible.

These other human minds can now in turn afford
valuable corroboratory evidence concerning the objec-
tive existence and permanence of material objects when
doubts as to the possibility of illusion are awakened.

Secondary acquisitions. — We have spoken so far of the
essential capabilities of touch : a word may be of interest
now on the special or accidental acquirements of this per-
cipient faculty. The degree to which the sense of touch can
be cultivated, and the fineness of the capacity of both
muscular and tactual sensations for being discriminated
appear truly amazing when thoughtfully considered. The
miller can by the sense of feeling distinguish variations in the
quality of flour utterly invisible to the eye. The clothier can
recognize subtile differences in the texture of silk, linen, or
velvet, of an equally minute character. In such universal
attainments as those of speaking, reading, writing, playing
the piano, shaving, and indeed in all mechanical arts, the
most delicate sensibility is exhibited. These actions involve
a complicated series of movements under the guidance of
muscular and tactual sensations which are distinguishable
by differences so faint that we are fairly lost in astonishment
at the infinitesimal forces governing thus infallibly the
seemingly easy process.

It is in the blind, however, that this sense reaches its
proper perfection. By them space is known and remembered
solely in terms of tactual and motor experience. Their
attention is concentrated on this field of cognition, and their
powers of memory devoted to its service. The increased
exercise and cultivation of the remaining senses when sight
is in abeyance, has the eftect of developing these faculties in
an extraordinary manner, and none of them more so than
that of touch. The blind, for instance, who have been taught
to read, can decipher the contents by passing their fingers


rapidly over type not much larger than the print of the
present work, with a facihty that seems ineredible to their
more fortunate brethren who make the attempt. Dr. Carpenter
relates of Laura Bridgman, the well-known deaf and dumb
mute, that she unhesitatingly recognized his brother " after
the lapse of a year from his previous interview by the ' feel '
of his hand."^ She estimates the age and frame of mind of
her visitors by feeling the wrinkles of their face, and it is said
that she can even perceive variation in intensity and pitch of
voice by feeling the throat.*^ John Metcalf, the celebrated
blind road-maker, was deemed an excellent jud^^^e of horses.
When a lad he was a favourite guide through the lanes and
marshes of his native county. As a young man he followed
the hounds on horseback across country, and on one occasion
won a three mile race round a circular course. These latter
feats, however, were performed rather by the sense of hearing
than of touch. To guide him in the race, he placed a man
with a bell at each post ; and in the hunting-field the cry of
the hounds, the intelligence of his horse, and his knowledge
of the country enabled him to keep a leading place. *"

Visual Perception. — As the formal object of
sight is merely coloured surface, the eye cannot
originally inform us of distance. This faculty, even
more than that of touch, has constituted a battle-
ground for the "nativistic" and "emipirical" theories.
The more thoroughgoing nativists have held that the
eye, or rather the visual organ consisting of both eyes,
has from the beginning the power of immediately
or intuitively apprehending the distance and relative
situation of objects, just as well as the ability of
perceiving differences of colour. Empiricists, on

^ Mental Physiology, § 127.

*> " Pressing thus on the throat of several persons successively,
she sometimes sportively attempts to imitate their voice with her
own in a way which shows that she does distinguish differences
of both loudness and pitch (paradoxical as the language may be)
without any conception or sensation whatever of sound." (Cf. Mind,
1879, pp. 166, 167.)

'' Smiles, Lives of Engineers, Yo\. p 210.


the other hand, deny to the eye all native capacity
of cognizing extension in any form. According to
their view, it is only by experience and association
that ocular sensations, which in themselves bear no
more reference to space than feelings of sound or
smell, are gradually construed into extended solid
objects. Here again, as before, it will be found
that truth lies in the mean. The primary percep-
tion of the eye is simply coloured surface; neither
distance, solidity, nor absolute magnitude is origi-
nally presented to us by this sense. These are
secondary or acquired perceptions, gained by
associating in experience various shades of colour,
and degrees of tension in the ocular muscles, with
different motor and tactual experiences. But surface
space is originally perceived directly.

The original presentation of superficial extension is very
vague. The central point of the retina is most sensitive, and
the shape of an external surface, e.g., of a triangle, is defined
by moving the line of direct vision round its outline. The
relative situation of the parts subtending different points on
the retina, and the intervals of space between them, vaguely
presented by the quantity of intermediate distinct sentient
points, similarly receive accurate determination by means of
the muscular sensations involved in bringing the central axis
of the eye to bear on them. In sight, as in touch, Lotze
amends the empirical doctrine by the hypothesis of " local
signs." Though the sensations of diff'erent points of the
retina are qualitatively diff'erent, he holds that there is
originally no presentation of extension. By association the
qualitative mark of any spot awakens a representation of the
quantity of muscular sensation requisite to direct the central
point towards the object subtended by that spot, and this,
he teaches, is all that spatial distance means. Greater or less
space is, in fact, merely the possibility of more or fewer
muscular feelings. (Cf. Metaphysic, Book III. c. iv.)

Here again, as in the development of tactual perception
the hypothesis of " local signs " may be accepted as a means


of explaining the determination of the relative positions and
comparative magnitudes of objects within the extended field
of vision, but it cannot account for the original presentation
of extension itself.

Immediate Perception of Surface Extension.

■ — The argument used to establish the direct per-
ception of extension by D'Alembert, Hamilton, and
others, has never been really answered. We will
adopt Dr. Porter's enunciation of the proof: " If
two or more bands of colour were present to the
infant which had never exercised touch or move-
ment, it must see them both at once ; and if it sees
them both, it must see them as expanded or ex-
tended ; otherwise it could not see them at all, nor
the line of transition or separation between them.
Or if a disc of red were presented in the midst of
and surrounded by a field of yellow or blue, or if a
bright band of red were painted so as to return as
a circle upon itself, on a field of black, the band
could not be traced by the eye without requiring
that the eye should contemplate as an extended
percept the included surface or disc of red."^

8 The Hicman Intellect, p. 155. Cf. also Balmez, Fundamental
Philosophy, Book II. c. xii.,and Hamilton, Metaph.\o\. II. pp. 165, 172.
This argument is restated in an effective manner by Mr. Mahaffy,
The Critical Philosophy, pp. 115 — 121. It is no reply to say that the
extent of colour perceived by a motionless eye is very small and its
outline vague. This is true, though not to the extent that Mill
and Dr. Bain would make out. It is conceded by them that the
retina is extended, and that a small circle of colour can be originally
apprehended by sight alone. This admits at once the leading con-
tention of the intuitive school. A circle of the one-tenth of an inch
in diameter is as truly extended as the orbit of a planet, while no
microscope can reveal space in a sound or an odour, and no
summation of these latter sensations can result in a surface
or a solid.


Experimental evidence. — This demonstration is reinfoixed
by the direct evidence of a number of experiments tried on
persons who had late in Hfe been couched for cataract.
The testimony from this line of investigation is unhappily
not yet in as satisfactory a condition as could be desired. It
is a significant comment on the lofty claims of some physio-
logical psychologists to find that the experiments on
Cheseldeu's patient still receive a leading place among the
most recent text-books. In spite of the supposed enormous
and fruitful advances of physiological psychology, that
venerable and oft-recounted incident, now nearly one hundred
and seventy years old, and claimed by both sides, is still
amongst the least unsatisfactory cases we possess. The best
experiment, however, on the whole, seems to be that ot
Dr. Franz, of Leipzig (1840). In the operations of both Franz
and Cheselden the subjects were intelligent boys of seventeen
and eighteen years of age. When, after the cataract had
been removed, the eyes of the patients were sufficiently
healed to be exposed to the light, a series of observations and
experiments were instituted in order to ascertain exactly how
much they could directly perceive by their newly-received
faculty. The points of importance best established were :
(1) that the newly-acquired sense presented to the mind a
field of colour extended in two dimensions of space ; (2) that
it did not afford a perception of the relative distances of
objects, all being apprehended in a confused manner as in
close proximity to the eye; (3) and that, consequently, no
information was given as to the absolute magnitude of things.
(4) In Franz's case, where the investigation was more skilfully
conducted than on the earlier occasion, the patient recognized
the identity between horizontal and perpendicular lines now
seen by the eye and those formerly known by touch. He
could similarly recognize square and round figures, though he
could not distinguish these from solid cubes and spheres.'*

" These two cases, and others of less value during the interval,
are reported in the I'liil. Trans, of the Royal Society. Dr. Carpenter,
Mental Philosophy, %l 161 and 167, alludes to some other instances,
and others again are cited by Helmholtz, but the two given above
are among the best. A large portion of the account of Franz's
case is transcribed from the Phil. Trans. 1841, into Mr. Mahafly's
Critical Philosophy, pp. 122 — 133, and in briefer form into Dr. M 'Cosh's
E:xam. of Mill, pp. 163—165. Hamilton's Metaph. Vol. II. pp. 177—
179, contains the Cheselden case at length. The best summary,
however, of all these cases is given in Preyer's Development of the
Intellect (1896), pp. 286— 317. The fact that the most recent case
recorded there is that of Franz, already fifty-six years old, is


Analogical argument. — The force of the evidence in favour
of the immediate apprehension of space of at least two
dimensions by the human infant is still further increased by
the fact that several of the lower animals are now proved to
possess a perfect appreciation of even three dimensions of
space at birth. Mr. Spalding established intuitive perceptions
in the case of chickens by covering their eyes with hoods as
soon as they left the shell, and so preventing all visual
experiences until they were strong enough for various experi-
ments. When the hoods were removed they immediately
showed their appreciation of spatial relations. " Often at the
end of two minutes," says Mr. Spalding, " they followed with
their eyes the movements of crawling insects, turning their
head with all the precision of an old fowl. In from two to
fifteen minutes they pecked at some speck or insect, showing
not merely an instinctive perception of distance, but an
original ability to judge, to measure distance, with some-
thing like infallible accuracy. . . . They never missed by
more than a hair's breadth, and that too, when the specks
aimed at were no bigger, and less visible, than the small dot
of an /."i"^ He shows a similar power of intuitive perception
to be possessed by young pigs and some other animals
physically well developed at birth. This positive proof of
the existence of intuitive apprehension of space of three
^limensions demonstrates in a striking manner the absurdity
of the imphcit assumption in associationist accounts of the
subject that immediate vision even of surface extension is

Mediate perception of Distance and Magnitude.

— That the human eye has not originally the capacity of
estimating distance is shown by such experiments as
those just cited; and by the fact that in mature life in
unusual circumstances, as for instance, at sea, we feel
at a great loss when we attempt to judge the length of
considerable intervals of space. The simple experi-
ment of closing one eye, especially when entering an
unfamiliar room, also shows how imperfect is our purely
visual appreciation of distance. And the various
illusions of painting, of the diorama, and of the stereo-
scope, all go to prove the truth that the apparently
immediate apprehension of the third dimension of space

'" Cf. Macmillan's Magazine, February, 1873; James, Vol. II.
pp. 394—400 ; and Preyer, The Senses and the Will, pp. 66, 235—241.



by sight is really an acquired perception, which
involves a rapid process of inference from numerous
visual signs.

In developed perception there are engaged many
factors whose presence and action are commonly
ignored. Starting from an originally indefinite appre-
hension of extended coloured surface, we find that
different perspective appearances, shades of colour,
and degrees of tension in the ocular muscles are asso-
ciated with longer or shorter distances to be moved
through in order to touch the coloured object. After a
sufficient number of experiences the visual appearance
suggests the appropriate amount of movement, and the
former becomes the symbol of the latter. The chief
elements in the process seem to be the following :

1. Focal adjustments — The single eye is subject to
different muscular sensations according to the varying
distance of the object up to an interval of twenty feet.
This is due to the self-regulating action of the ciliary
muscle, which increases or decreases the convexity of
the crystalline lens so as to adjust the focus to a shorter
or longer range.

2. Axial adjustment. — The muscular sensations
awakened by converging the axes of both ej'es to meet
in a point, vary according as the object is nearer or
farther within a space of two hundred yards.

3. Mathematical perspective. — The size of the retinal
image and the apparent size of an object change with
the distance of the latter ; consequently, if its real
magnitude is already known, we have the means of
determining how remote it is. It is for this purpose
the painter is accustomed to introduce the figure of a
man or of some well-known animal into the foreground
of his pictures.

4. Aerial perspective. — Finally, changes of colour, and
the greater or less haziness in the outlines of objects
becomes by experience the signs of a longer or shorter
interval between them and us.

Our visual perception of the magnitude of an object

11 Cf. Le Conte, Sight, Part II. c. v.


is an inference from its apparent size and presumed
distance, and most of the steps just given may enter into
the estimate. Thus, in judging the dimensions of an
unfamiHar object, such as a rock, or a mound of earth
afar off", we are led to form an idea of the length of
space intervening by the number and apparent magni-
tude of known objects between us and the point in
question, by the apparent size of other known figures,
such as those of men or animals situated in its vicinity,
and by the clearness or mistiness of the outlines of the
object and of its neighbours. Having thus estimated
the distance we infer the real from the apparent magni-
tude of the object.

Mutual aid of Sight and Touch. — The education of tlie
sense of sight proceeds concomitantly with that of the
faculty of tactual and motor sensations. Mutually
aiding each other their progress is very rapid. The
advantages gained by touch through the consciousness
of double-contact are now largely increased by the
addition of a power which can apprehend in an instant
the entire contour of the body, and the situation of the
various agents acting upon it. The length of the sweep
of the arm or leg are known not merely in the dim
terms of subjective motor feelings, but through the
fine visual perceptions of space. The wide range of
the eye, and those other numerous excellences which
have been detailed in describing this sense, confer upon
its acts the power of arousing with marvellous facility
and speed the representation of associated tactual and
muscular sensations. By this singularl}' perfect appro-
priation of the acquisitions of touch, vision is enabled
to inform us in an easy, rapid, and admirable manner
of a multitude of the tangible properties of things which
we could never, or but by an incredible amount of labour,
ascertain through actual contact. At the same time,
the control of the organ of sight is secured by the ciliary
muscles ; and while we watch the movement of the
arm, the muscular sensations of the eye reveal the
quantity of change in its own direction, the degree of
convergence of the optic axes, and the increase or
decrease in the copyexity of the cr3'stalline lens. In


this way by the mutual co-operation of the two faculties
our knowledge of the most important attributes of
matter is elaborated.

Vision, unlike touch, taste, and smell, does not seem to be
capable of much advance in range or refinement beyond what
it normally reaches. The skill with which the Indian can
follow a trail and the sailor recognize an object at sea seem
among the most remarkable effects of special education of
this sense. Unlike the other faculties, sight is normally
developed almost up to its full maximum efficiency.

Binocular Vision. — A large district of the spatial scene
apprehended by sight is common to both eyes, but the out-
skirts on either side extend beyond the binocular field of
vision, and can be reached only by a single organ. In the
perception of distant objects within the common field there is
ordinarily formed on each of the retinas a similar picture,
but things seen in our immediate neighbourhood offer a
different appearance to the right and to the left eye. This
fact has given rise to the problem of single vision. Why with
two eyes do we not see two objects instead of one ? Various
explanations have been suggested. One view supposes that
we originally saw double, but by experience have learned to
assign the two images to a single cause. Another maintains
that the two eyes form really but one organ. There are, it is
held, "identical or corresponding points " on the two retinas,
and pairs of nerves running from these to the brain coalesce,
so that the two stimuli are fused into a single final excitation
awakening but one sensation. Other writers have asserted
that although the two eyes see different pictures yet, at any
given time, we attend only to one.

As regards the last hypothesis it is undoubtedly true that
one eye is commonly more active than the other, and most
people will find that the right is more efficient than the left ;
still it is going beyond the evidence to assume that our
attention is normally so concentrated upon the activity of
one eye that the other may be thrown out of account. In
favour of the second view may be urged the authority of
several distinguished German physiologists starting with
Miiller fifty years ago, who consider the anatomical evidence
to be on the whole in support of the physical explanation.
It is also maintained that if the two retinas were really
subjects of two distinct sensations, careful reflexion and
examination of our consciousness ought to enable us to
distinguish them. Finally, it is held that the analogy in the
case of young animals constitutes a forcible argument. If


the two eyes are co-ordinated so as to originate a sin£;lc
perception from the beginning in these latter, as is un-
doubtedly the case, it is reasonable to suppose, where there
is no positive evidence to the contrary, that the same holds
for the young infant.

On the other side it is argued : (a) That more accurate
knowledge of anatomy does not bear out the nativistic
position. {b) That points physiologically not " corres-
ponding " sometimes give rise to a single perception, whilst
on other occasions points that ought to correspond excite
double vision. In abnormal conditions, such as squinting,
where the derangement is permanent, vision is single, in spite
of the non-correspondence of identical points, and when the
irregularity has been removed by surgical means, so that the
two axes get into a normal position, double vision arises for a
time, but by continued experience passes again into single
vision. {c) Some writers contend that the " conflict or
rivalry of the retinas," which takes place when the two eyes
are made to contemplate different colours, is in favour of the
empirical theory. If there was a real physical fusion of the
nerve currents from the retinas to the brain, then we ought
to have a sensation of an intermediate character and not, as
is the case at present, an alternative struggling sensation of
each. A modification of this experiment, however, is held
by others to support the nativistic theory.'^ {d) It is also
urged that the illusion produced by the stereoscope, where
two dissimilar pictures presented to the different eyes give
rise to the perception of a single object, confirms the empirical

On the whole that view seems to us to be nearest to the
truth which, while admitting a certain degree of natural
harmony in the structure of the two instruments, yet assigns
to experience the development and perfection of binocular

^- Cf. Wyld, Physics and Philosophy of the Senses, pp. 226, 227.

'^ The stereoscope is an instrument, invented by Wheatstone,
and improved by Brewster, in which slightly dissimilar pictures,
such as would be presented to the right and left retinas by a neigh-
bouring solid object, are simultaneously set separately each before
the appropriate eye. The result is an irresistible conviction of a
single solid object. The empirical school hold this fact to establish
that single vision is really an interpretation of two mental images

Online LibraryMichael MaherPsychology: empirical and rational → online text (page 14 of 63)