PERCEPTION OBJECTIVELY REGARDED
It will be remembered that the task upon which we are at present
engaged is the definition of “knowledge” as a phenomenon discoverable
by an outside observer. When we have said what we can from this
objective standpoint, we will ask ourselves whether anything further,
and if so what, is to be learnt from the subjective standpoint, in
which we take account of facts which can only be discovered when the
observer and the observed are the same person. But for the present we
will resolutely confine ourselves to those facts about a human being
which another human being can observe, together with such inferences as
can be drawn from these facts.
The word “knowledge” is very ambiguous. We say that Watson’s rats
“know” how to get out of mazes, that a child of three “knows” how to
talk, that a man “knows” the people with whom he is acquainted, that
he “knows” what he had for breakfast this morning, and that he “knows”
when Columbus first crossed the ocean. French and German are less
ambiguous, since each has two words for different kinds of “knowing”,
which we tend to confuse in our thoughts because we confuse them in our
language. I shall not attempt as yet to deal with knowledge in general,
but rather with certain less general concepts which would ordinarily
be included under “knowledge”. And first of all I will deal with
perception--not as it appears to the perceiver, but as it can be tested
by an outside observer.
Let us try, first, to get a rough preliminary view of the sort of
thing we are going to mean by “perception”. One may say that a man
“perceives” anything that he notices through his senses. This is not
a question of the sense-organs alone, though they are a necessary
condition. No man can perceive by sight what is not in his field of
vision, but he may look straight at a thing without perceiving it. I
have frequently had the experience--supposed to be characteristic of
philosophers--of looking everywhere for my spectacles although they
were before my eyes when my search began. We cannot therefore tell
what a man is perceiving by observing his sense-organs alone, though
they may enable us to know that he is _not_ perceiving something.
The observer can only know that a man is perceiving something if the
man reacts in some appropriate manner. If I say to a man “please
pass the mustard” and he thereupon passes it, it is highly probable
that he perceived what I said, although it _may_ of course be a mere
coincidence that he passed it at that moment. But if I say to him “the
telephone number you want is 2467” and he proceeds to call that number,
the odds against his doing so by mere chance are very great--roughly
10,000 to 1. And if a man reads aloud out of a book, and I look over
his shoulder and perceive the same words, it becomes quite fantastic to
suppose that he does not perceive the words he is uttering. We can thus
in many cases achieve practical certainty as to some of the things that
other people are perceiving.
Perception is a species of a wider genus, namely _sensitivity_.
Sensitivity is not confined to living things; in fact it is best
exemplified by scientific instruments. A material object is said to
be “sensitive” to such and such a stimulus, if, when the stimulus is
present, it behaves in a way noticeably different from that in which
it behaves in the absence of the stimulus. A photographic plate is
sensitive to light, a barometer is sensitive to pressure, a thermometer
to temperature, a galvanometer to electric current, and so on. In all
these cases, we might say, in a certain metaphorical sense, that an
instrument “perceives” the stimulus to which it is sensitive. We do not
in fact say so; we feel that perception involves something more than we
find in scientific instruments. What is this something more?
The traditional answer would be: consciousness. But this answer,
right or wrong, is not what we are seeking at the moment, because we
are considering the percipient as he appears to an outside observer,
to whom his “consciousness” is only an inference. Is there anything
in perception as viewed from without that distinguishes it from the
sensitivity of a scientific instrument?
There is, of course, the fact that human beings are sensitive to
a greater variety of stimuli than any instrument. Each separate
sense-organ can be surpassed by something made artificially sensitive
to its particular stimulus. Photographic plates can photograph stars
that we cannot see; clinical thermometers register differences of
temperature that we cannot feel; and so on. But there is no way of
combining a microscope, a microphone, a thermometer, a galvanometer,
and so on, into a single organism which will react in an integral
manner to the combination of all the different stimuli that affect its
different “sense-organs”. This, however, is perhaps only a proof that
our mechanical skill is not so great as it may in time become. It is
certainly not enough to define the difference between a dead instrument
and a living body.
The chief difference--perhaps the only one from our present point of
view--is that living bodies are subject to the law of association or
of the “conditioned reflex”. Consider, for instance, an automatic
machine. It has a reflex which makes it sensitive to pennies, in
response to which it gives up chocolate. But it never learns to give
up chocolate on merely seeing a penny, or hearing the word “penny”.
If you kept it in your house, and said “Abracadabra” to it every time
you inserted a penny, it would not in the end be moved to action by
the mere word “Abracadabra”. Its reflexes remain unconditioned, as
do some of ours, such as sneezing. But with us sneezing is peculiar
in this respect--hence its unimportance. Most of our reflexes can be
conditioned, and the conditioned reflex can in turn be conditioned
afresh, and so on without limit. This is what makes the reactions of
the higher animals, and especially of man, so much more interesting
and complicated than the reactions of machines. Let us see whether
this one law will suffice to distinguish perception from other forms of
sensitivity.
The variability in a human being’s responses to a given stimulus
has given rise to the traditional distinction between cognition and
volition. When one’s rich uncle comes for a visit, smiles are the
natural response; after he has lost his money, a colder demeanour
results from the new conditioning. Thus the reaction to the stimulus
has come to be divided into two parts, one purely receptive and
sensory, the other active and motor. Perception, as traditionally
conceived, is, so to speak, the end term of the receptive-sensory part
of the reaction, while volition (in its widest sense) is the first term
of the active-motor part of the reaction. It was possible to suppose
that the receptive part of the reaction would be always the same for
the same stimulus, and that the difference due to experience would
only arise in the motor part. The last term of the passive part, as it
appears to the person concerned, was called “sensation”. But in fact
the influence of the law of conditioned reflexes goes much deeper than
this theory supposed. As we saw, the contraction of the pupil, which is
normally due to bright light, can be conditioned so as to result from
a loud noise. What we see depends largely upon muscular adjustments
of the eyes, which we make quite unconsciously. But apart from the
contraction of the pupil only one of them is a true reflex, namely
turning the eyes towards a bright light. This is a movement which
children can perform on the day of their birth; I know this, not merely
from personal observation, but also, what is more, from the text-books.
But new-born infants cannot follow a moving light with their eyes, nor
can they focus or accommodate. As a consequence, the purely receptive
part of their reaction to visual objects, in so far as this reaction is
visual, is different from that of adults or older children, whose eye
muscles adjust themselves so as to see clearly.
But here again all sorts of factors enter in. Innumerable objects are
in our field of vision, but only some (at most) are interesting to us.
If some one says “look, there’s a snake”, we adjust our eyes afresh
and obtain a new “sensation”. Then, when the purely visual part is
finished, there are stimulations, by association, of other centres
in the brain. There are pictures, in Köhler’s book, of apes watching
other apes on the top of insecure piles of boxes, and the spectators
have their arms raised in sympathetic balancing movements. Any one
who watches gymnastics or skilful dancing is liable to experience
sympathetic muscular contractions. Any visual object that we might be
touching will stimulate incipient touch reactions, but the sun, moon,
and stars do not.
Conversely, visual reactions may be stimulated through association with
other stimuli. When motor-cars were still uncommon, I was walking one
day with a friend when a tire punctured in our neighbourhood with a
loud report. He thought it was a revolver, and averred that he had seen
the flash. In dreams, this sort of mechanism operates uncontrolled.
Some stimulus--say the noise of the maid knocking at the door--becomes
interpreted in fantastic ways which are governed by association. I
remember once dreaming that I was in an inn in the country in Germany
and was wakened by a choir singing outside my window. Finally I
really woke, and found that a spring shower was making a very musical
noise on the roof. At least, I heard a very musical noise, and now
re-interpreted it as a shower on the roof. This hypothesis I confirmed
by looking out of the window. In waking life we are critical of the
interpretative hypotheses that occur to us, and therefore do not make
such wild mistakes as in dreams. But the creative, as opposed to the
critical, mechanism is the same in waking life as it is in dreams:
there is always far more richness in the experience than the sensory
stimulus alone would warrant. All adaptation to environment acquired
during the life of the individual might be regarded as learning to
dream dreams that succeed rather than dreams that fail. The dreams we
have when we are asleep usually end in a surprise: the dreams we have
in waking life are less apt to do so. Sometimes they do, as when pride
goes before a fall; but in that case they are regarded as showing
maladjustment, unless there is some large external cause, such as
an earthquake. One might say that a person properly adapted to his
environment is one whose dreams never end in the sort of surprise that
would wake him up. In that case, he will think that his dreams are
objective reality. But if modern physics is to be believed, the dreams
we call waking perceptions have only a very little more resemblance to
objective reality than the fantastic dreams of sleep. They have some
truth, but only just so much as is required to make them useful.
Until we begin to reflect, we unhesitatingly assume that what we
see is really “there” in the outside world, except in such cases as
reflections in mirrors. Physics and the theory of the way in which
perceptions are caused show that this naive belief cannot be quite
true. Perception may, and I think does, enable us to know something of
the outer world, but it is not the direct revelation that we naturally
suppose it to be. We cannot go into this question adequately until we
have considered what the philosopher has to learn from physics; I am
merely giving, by anticipation, the reasons for regarding perception
as a form of reaction to the environment, displayed in some bodily
movement, rather than as a form of knowledge. When we have considered
further what constitutes knowledge, we may find that perception is,
after all, a form of knowledge, but only because knowledge is not
quite what we naturally suppose it to be. For the present, let us
stick to the view of perception that can be obtained by the external
observer, _i.e._ as something displayed in the manner of reacting to
the environment.
From the point of view of the external observer, perception is
established just like any other causal correlation. We observe that,
whenever a certain object stands in a certain spatial relation to
a man’s body, the man’s body makes a certain movement or set of
movements; we shall then say that the man “perceives” the object. So
the new-born baby turns its eyes slowly towards a bright light which
is not in the centre of the field of vision; this entitles us to say
that the baby “perceives” the light. If he is blind, his eyes do not
move in this way. A bird flying about in a wood does not bump into the
branches, whereas in a room it will bump into the glass of the window.
This entitles us to say that the bird perceives the branches but not
the glass. Do we “perceive” the glass or do we merely know that it
is there? This question introduces us to the complications produced
by association. We know by experience, from the sense of touch, that
there is usually glass in window-frames; thus it makes us react to
the window-frames as if we could see the glass. But sometimes there
is no glass, and still we shall perhaps behave as if there were. If
this can happen, it shows that we do not perceive the glass, since our
reaction is the same whether there is glass or not. If, however, the
glass is coloured, or slightly distorting, or not perfectly clean,
a person accustomed to glass will be able to distinguish a frame
containing glass from one which has none. In that case it is more
difficult to decide whether we are to say that he “perceives” the
glass or not. It is certain that perception is affected by experience.
A person who can read perceives print where another would not. A
musician perceives differences between notes which to an untrained ear
are indistinguishable. People unaccustomed to the telephone cannot
understand what they hear in it; but this is perhaps not really a case
in point.
The difficulty we are considering arises from the fact that a human
body, unlike a scientific instrument, is perpetually changing its
reaction to a given stimulus, under the influence of the law of
association. Moreover, the human body is always doing something.
How, then, are we to know whether what it is doing is the result of
a given stimulus or not? In most cases, however, this difficulty is
not very serious, particularly when we are dealing with people old
enough to speak. When you go to the oculist he asks you to read a
number of letters growing gradually smaller; at some point you fail.
Where you have succeeded, he knows that you have perceived enough to
make out what letter it is. Or you take a pair of compasses and press
the points into a man’s back, asking him if he feels two pricks or
only one. He may say one when the two points are near together; if he
is on his guard against this error he may say two when in fact there
is only one. But if the points are sufficiently far apart he will
never make a mistake. That is to say, the bodily movement consisting
in pronouncing the word “two” will invariably result from a certain
stimulus. (Invariably, I mean, for a given subject on a given day.)
This entitles us to say that the man can perceive that there are two
points provided they are not too near together. Or you say: “What can
you see on the horizon?” One man says, “I see a ship”. Another says, “I
see a steamer with two funnels”. A third says, “I see a Cunarder going
from Southampton to New York”. How much of what these three people say
is to count as perception? They may all three be perfectly right in
what they say, and yet we should not concede that a man can “perceive”
that the ship is going from Southampton to New York. This, we should
say, is inference. But it is by no means easy to draw a line; some
things which are, in an important sense, inferential, must be admitted
to be perceptions. The man who says “I see a ship” is using inference.
Apart from experience, he only sees a queerly shaped dark dot on a blue
background. Experience has taught him that that sort of dot “means” a
ship; that is to say, he has a conditioned reflex which causes him to
utter, aloud or to himself, the word “ship” when his eye is stimulated
in a certain way. To disentangle what is due to experience, and what
not, in the perceptions of an adult, is a hopeless task. Practically,
if a word comes without previous verbal intermediaries, the ordinary
man would include what the word means in the perception, while he would
not do so if the man arrives at the word after verbal preliminaries,
overt or internal. But this is itself a question of familiarity. Show
a child a pentagon, and he will have to count the sides to know how
many there are; but after a little experience of geometrical figures,
the word “pentagon” will arise without any previous words. And in any
case such a criterion is theoretically worthless. The whole affair is a
matter of degree, and we cannot draw any sharp line between perception
and inference. As soon as this is realised, our difficulties are seen
to be purely verbal and therefore unimportant.
It will be observed that we are not attempting at present to say what
constitutes perception, but only what kind of behaviour on the part
of a person whom we are observing will justify us in saying that he
has perceived this or that feature of his environment. I suggest that
we are justified in saying that a man “perceives” such a feature if,
throughout some such period as a day, there is some bodily act which
he performs whenever that feature is present, but not at any other
time. This condition is clearly sufficient, but not necessary--that
is to say, there may be perception even when it is not fulfilled. A
man’s reaction may change through conditioning, even in so short a
period as a day. Again, there may be a reaction, but one which is too
slight to be observable; in this case the criterion of perception
is theoretically satisfied, but not practically, since no one can
know that it is. We often have evidence later on that something was
perceived, although at the moment there was no discoverable reaction.
I have frequently known children repeat afterwards some remark which,
at the time, they seemed not to have heard. This sort of case affords
another kind of evidence of perception, namely, the evidence afforded
by a delayed response. Some people will sit silent and impassive in a
company of talkers, giving no evidence that they are listening; yet
they may go home and write down the conversation verbatim in their
journals. These are the typical writers of memoirs. More remarkable
still, I know one man--a man of genius, it is true--who talks
incessantly, who yet, after meeting a total stranger, knows exactly
what the stranger would have said if he had been given the chance.
How this is managed, I do not know; but such a man is rightly called
“perceptive”.
Obviously, in dealing with human beings old enough to talk, words
afford the best evidence of perception. A man’s verbal responses to
perceptive situations do not change much after the first few years of
life. If you see a kingfisher, and at the same moment your companion
says “there’s a kingfisher”, that is pretty conclusive evidence that
he saw it. But, as this case illustrates, our evidence that some one
else has perceived something always depends upon our own perceptions.
And our own perceptions are known to us in a different way from that
in which the perceptions of others are known to us. This is one of
the weak spots in the attempt at a philosophy from the objective
standpoint. Such a philosophy really assumes knowledge as a going
concern, and takes for granted the world which a man derives from
his own perceptions. We cannot tackle all our philosophical problems
by the objective method, but it is worth while to proceed with it as
far as it will take us. This whole question of perception will have
to be attacked afresh from a different angle, and we shall then find
reason to regard the behaviouristic standpoint as inadequate, though
valid so far as it goes. We have still, however, a long road to go
before we shall be driven to consider the subjective standpoint;
more particularly, we have to define “knowledge” and “inference”
behaviouristically, and then, making a new start, to consider what
modern physics makes of “matter”. But for the moment there are still
some things to be said about perception from the objective standpoint.
It will be seen that, according to our criterion of perception, an
object perceived need not be in contact with the percipient’s body. The
sun, moon, and stars are perceived according to the above criterion.
In order, however, that an object not in contact with the body should
be perceived, there are physical as well as physiological conditions
to be fulfilled. There must be some physical process which takes place
at the surface of the body when the object in question is suitably
situated, but not otherwise; and there must be sense-organs capable of
being affected by such a process. There are, as we know from physics,
many processes which fulfil the necessary physical conditions, but
fail to affect us through the inadequacy of our sense-organs. Waves of
a certain sort make sound, but waves of exactly the same sort become
inaudible if they are too short. Waves of a certain sort make light,
but if they are too long or too short they are invisible. The waves
used in wireless are of the same sort as those that make light, but are
too long. There is no reason _a priori_ why we should not be aware of
wireless messages through our senses, without the need of instruments.
X-rays are also of the same sort as those that make light, but in this
case they are too short to be seen. They might render the objects from
which they come visible, if we had a different sort of eye. We are not
sensitive to magnetism, unless it is enormously powerful; but if we
had more iron in our bodies, we might have no need of the mariner’s
compass. Our senses are a haphazard selection of those that the nature
of physical processes renders possible; one may suppose that they have
resulted from chance variation and the struggle for existence.
It is important to observe that our perceptions are very largely
concerned with form or shape or structure. This is the point emphasised
by what is called “_Gestaltpsychologie_”, or psychology of form.
Reading is a case in point. Whether we read black letters on white
paper or white letters on a blackboard is a matter which we hardly
notice; it is the forms of the letters that affect us, not their colour
or their size (so long as they remain legible). In this matter, the
sense of sight is pre-eminent, although blind men (and others to a less
degree) can acquire a good knowledge of form by the sense of touch.
Another point of importance about our perceptions is that they give us,
within limits, a knowledge of temporal sequence. If you say to a man
“Brutus killed Cæsar”, and then “Cæsar killed Brutus”, the difference
between the two statements is likely to be perceived by him if he
is listening; in the one case he will say “of course”, in the other
“nonsense”, which is evidence of his having different perceptions in
the two cases, according to our definition. Further, if you ask him
what the difference is, he can tell you that it is a difference in the
order of the words. Thus time-order within a short period of time is
clearly perceptible.
The objective method, which we have been applying in this chapter, is
the only possible one in studying the perceptions of animals or of
infants before they can talk. Many animals too low in the scale of
evolution to have eyes are yet sensitive to light, in the sense that
they move towards it or move away from it. Such animals, according to
our criterion, perceive light, though there is no reason to suppose
that they perceive colour or visual form or anything beyond the bare
presence of light. We can perceive the bare presence of light when our
eyes are shut; perhaps one may imagine their sensitiveness to be more
or less analogous in its limitations.
It is not to be supposed, in any case, that “perceiving” an object
involves knowing what it is like. That is quite another matter.
We shall see later that certain inferences, of a highly abstract
character, can be drawn from our perceptions to the objects perceived;
but these inferences are at once difficult and not quite certain. The
idea that perception, in itself, reveals the character of objects,
is a fond delusion, and one, moreover, which it is very necessary to
overcome if our philosophy is to be anything more than a pleasant
fairy-tale.