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On the hypothesis that our ideas of distance are acquired, it remains for us to investigate the circumstances Circumstances which which assist us in forming our judgment respect
utkt u„ in forming mg them We sbaU fiu)J that thfiy may fee ar.
^•^713^ TMnSed under *wo heads> 8on,e of them dependpend, i. On certain ing upon certain states of the eye itself, and othsutes of the eye. er8 upon various accidents that occur in the
appearance of the objects. With respect to distances that are so short as to require the adjustment of the eye in order to obtain distinct vision, it appears that a certain voluntary effort is necessary to produce the desired effect: this effort, whatever may be its nature, causes a corresponding sensation, the amount of which we learn by experience to appreciate; and thus, through the medium of association, we acquire the power of estimating the distance with sufficient accuracy.
When objects are placed at only a moderate distance, but not such as to require the adjustment of the eye, in directing the two eyes to the object we incline them inwards; as is the case likewise with very short distances: so that what are termed the axes of the eyes, if produced, would make an angle at the object, the angle varying inversely as the distance. Here, as in the former case, we have certain perceptions excited by the muscular efforts necessary to produce a proper inclination of the axes, and these we learn to associate with certain distances. As a proof that this is the mode by which we judge of those distances where the optic axes form an appreciable angle, when the eyes are both directed to the same object, while the effort of adjustment is not perceptible, — it has been remarked, that persons who are deprived of the sight of one eye, are incapable of forming a correct judgment in this case.
When we are required to judge of still greater distances, where the object is so remote as that the axes of the
. ncertancon - ^wq eg are paraue] we are no longer able to
tions of the object. . .
form our opinion from any sensation in the eye itself. In this case, we have recourse to a variety of circumstances connected with the appearance of the object; for example, its apparent size, the distinctness with which it is seen, the vividness of its colors, the number of intervening objects, and other similar accidents, all of which obviously depend upon previous experience, and which we are in the habit of associating with different distances, without, in each particular case, investigating the cause on which our judgment is founded.
The conclusions of science seem in this case to be decisive; and yet the whole question is thrown into doubt by the analogy of the lower animals. If in man the perception of distance be not original but acquired, the perception of distance must Berkeley's proof be aiso acquired by them. But as this is not the
thrown into doubt by . -, . • * .1 • « ,*
case in regard to animals, this confirms the rea
the analogy of the . ', . ,
lower animals. sonmg ot those who would explain the percep
tion of distance in man, as an original, not as an
acquired, knowledge. That the Berkeleian doctrine is opposed by
the analogy of the lower animals, is admitted by one of its most
intelligent supporters, — Dr. Adam Smith.1
"That, antecedent to all experience," says Smith, "the young of at least the greater part of animals possess some
Adam Smith quoted. . . .-,.,.., L
instinctive perception ot this kind, seems abundantly evident. The hen never feeds her young by dropping the food into their bills, as the linnet and the thrush feed theirs. Almost as soon as her chickens are hatched, she does not feed them, but carries them to the field to feed, where they walk about at their ease, it would seem, and appear to have the most distinct perception of all the tangible objects which surround them. We may often see them, accordingly, by the straightest road, run to and pick up any little grains which she shows them, even at the distance of several yards; and they no sooner come into the light than they seem to understand this language of Vision as well as they ever do afterwards. The young of the partridge and the grouse seem to have, at the same early period, the most distinct perceptions of the same kind. The young partridge, almost as soon as it comes from the shell, runs about among long grass and corn, the young grouse among long heath; and would both most essentially hurt themselves if they had not the most acute as well as distinct perception of the tangible objects which not only surround them but press upon them on all sides. This is the case, too, with the young of the goose, of the duck, and, so far as I have been able to observe, with those of at least the greater part of the birds which make their nests upon the ground, with the greater part of those which are ranked by Linnaeus in the orders of the hen and the goose, and of many of those longshanked and wading birds which he places in the order that he distinguishes by the name of Grallaa.
"It seems difficult to suppose that man is the only animal of which the young are not endowed with some instinctive perception of this kind. The young of the human species, however, continue so long in a state of entire dependency, they must be so long carried about in the arms of their mothers or of their nurses, that such an instinctive perception may seem less necessary to them than to any other race of animals. Before it could be of any use to them, observation and experience may, by the known principle of the association of ideas, have sufficiently connected in their young minds each visible object with the corresponding tangible one which it is fitted to represent. Nature, it may be said, never bestows upon any animal any faculty which is not either necessary or useful, and an instinct of this kind would be altogether useless to an animal which must necessarily acquire the knowledge which the instinct is given to supply, long before that instinct could be of any use to it. Children, however, appear at so very early a period to know the distance, the shape, and magnitude of the different tangible objects which are presented to them, that I am disposed to believe that even they may have some instinctive perception of this kind ; though possibly in a much weaker degree than the greater part of other animals. A child that is scarcely a month old, stretches out its hands to feel any little plaything that is presented to it. It distinguishes its nurse, and the other people who are much about it, from strangers. It clings to the former, and turns away from the latter. Hold a small looking-glass before a child of not more than two or three months old, and it will stretch out its little arms behind the glass, in order to feel the child which it sees, and which it imagines is at the back of the glass. It is deceived, no doubt; but even this sort of deception sufficiently demonstrates that it has a tolerably distinct apprehension of the ordinary perspective of Vision, which it cannot well have learnt from observation and experience."
1 See Euayi— Of the External Senses, p. 299—3M, edit, 1800. — Ed.
THE PRESENTATIVE FACULTY.
Hating, in our last Lecture, concluded the consideration of External Perception, I may now briefly recapitulate Principal points of certain results of the discussion, and state in what difference between the principal respects the doctrine I would maintain, Author', doctrine of djffers from that 0f Rejd and Stewart, whom I
Perception, and that , , . j . ... .. ,.
of Reid and Stewart. s«PP°se always to hold, in reality, the system of
an Intuitive Perception.
In the first place, — in regard to the relation of the external object
to the senses. The general doctrine on this sub
1. in regard to the ject js tnus gjven by Reid : "A law of our nature
relation of the exter- .. .. . ., -, ■ .
. .. a regarding perception is, that we perceive no ob
ae,. ject, unless some impression is made upon the
organ of sense, either by the immediate application of the object, or by some medium which passes between the object and the organ. In two of our senses, viz., Touch and Taste, there must be an immediate application of the object to the organ. In the other three, the object is perceived at a distance, but still by means of a medium, by which some impression is made upon the organ." l
Now this, I showed you, is incorrect. The only object ever perceived is the object in immediate contact, — in immediate relation, with the organ. What Reid, and philosophers in general, call the distant object, is wholly unknown to Perception; by reasoning we may connect the object perceived with certain antecedents, — certain causes; but these, as the result of an inference, cannot be the objects of perception. The only objects of perception are in all the senses equally immediate. Thus the object of my vision at present is not the paper or letters at a foot from my eye, but the rays of light reflected from these upon the retina. The object of your hearing is not the vibrations of my larynx, nor the vibrations of the intervening air; but the vibrations determined thereby in the cavity of the internal ear, and in immediate contact with the auditory nerves. In both senses, the external object perceived is the last effect of a series of unperceived causes. But to call these unperceived causes the object of perception, and to call the perceived effect, — the real object, only the medium of perception, is either a gross error or an unwarrantable abuse of language. My concluin all the senses, the gion ■ therefore, that, in all the senses, the ex
1 Intellectual Powers, Essay ii. c. ii. [ Works, p. 247. — Ed.]
external object in con- ..... . . .
tact with the organ. tcrnal obJect ls m contact with the organ, and
thus, in a certain signification, all the senses are
only modifications of Touch. This is the simple fact, and any other
statement of it is either the effect or the cause of misconception.
In the second place, — in relation to the number and consecution
of the elementary phenomena, —it is, and must
2. in regard to the be, admitted, on all hands, that perception must
number and consecu- , 111 * j» Ai. 1
„ ... , , be preceded by an impression of the external
tiou of the elementary r J T
phenomena. object on the senses ; in other words, that the
material reality and the organ must be brought into contact, previous to, and as the condition of, an act of this faculty. On this point there can be no dispute. But the case is different in regard to the two following. It is asserted by philosophers in general: — 1°. That the impression made on the organ must be propagated to the brain, before a cognition of the object Common doctrine of t;l^es piace m tne mind, — in other words, that
philosophers regard- ... 31-1
.. , , an omanic action must precede and determine
lug the organic im- _ & r
pression. the intellectual action ; and, 2°. That Sensation
Proper precedes Perception Proper. In regard
to the former assertion, — if by this were only meant, that the mind
does not perceive external objects out of relation to its bodily organs,
and that the relation of the object to the organism, as the condition
of perception, must, therefore, in the order of nature, be viewed as
prior to the cognition of that relation,—no ob
n w a respec n- jsection could be made to the statement. But if
accurate. . . .
it be intended, as it seems to be, that the organic affection precedes in the order of time the intellectual cognition, — of this we have no proof whatever. The fact as stated would be inconsistent with the doctrine of an intuitive perception; for if the organic affection were chronologically prior to the act of knowledge, the immediate perception of an object different from our bodily senses would be impossible, and the external world would thus be represented only in the subjective affections of our own organism. It is, therefore, more correct to hold, that the corporeal move