motor response is frequently exercised, short-circuiting takes place
(see p. 338), and the stimulus word arouses the motor response
directly. Short-circuiting follows the law of combination very
nicely. Let a stimulus S arouse an idea I and this in turn a motor
act M. S--I--M represents the linkages used. But undoubtedly there
is a weak pre-existing linkage directly across from S to M, and this
gets used to a slight degree, strictly according to the conditioned
reflex diagram, with I playing the part of the effective stimulus in
arousing M, and S the part of the originally ineffective stimulus.
By dint of being exercised in this way, the linkage S--M becomes
strong enough to arouse the motor response directly, and I is then
very likely to be left out altogether.]
{406}
2. Response by analogy and association by similarity.
When an object reminds me of a similar object, that is association by
similarity. But suppose I actually take the object to be the similar
object, and behave towards it accordingly; then my reaction is called
"response by analogy". Once, when far from home, I saw a man whom I
took to be an acquaintance from my home town, and stepped up to him,
extending my hand. He did not appear very enthusiastic, and informed
me that, in his opinion, I had made a mistake. This was response by
analogy, but if I had simply said to myself that that man looked like
my acquaintance, that would have been association by similarity.
Really, association by similarity is the more complex response, for it
involves response to the points of newness in the present object, as
well as to the points of resemblance to the familiar object, whereas
response by analogy consists simply in responding to the points of
resemblance.
Response by analogy often appears in little children, as when they
call all men "papa"' or as when they call the squirrel a "kitty" when
first seen. If they call it a "funny kitty", that is practically
association by similarity, since the word "funny" is a response to the
points in which a squirrel is different from a cat, while the word
"kitty" is a response to the points of resemblance.
But response by analogy is not always so childish or comic as the
above examples might seem to imply. When we respond to a picture by
recognizing the objects depicted, that is response by analogy, since
the pictured object is only {407} partially like the real object; a
bare outline drawing may be enough to arouse the response of "seeing"
the object. Other instances of response by analogy will come to light
when, in the next chapter, we come to the study of perception.
[Illustration: Fig. 58.--Response by analogy. The letters, A, B, X,
Y, represent the several stimuli that make up the original object, and
each of them becomes well linked with their common response (seeing
the object, and perhaps naming it). When the linkage between X and Y
and the response has become strong, a similar object, presenting X and
Y along with other new stimuli, C and D, appears, and arouses the old
response, by virtue of the now-effective linkage from X and Y to this
response.]
[Illustration: Fig. 59.--Association by similarity. Everything here as
in the previous diagram, except that C and D get a response in
addition to that aroused by X and Y, and so the new object is seen to
be new, while at the same time it recalls the old object to mind.]
The machinery of response by analogy is easily understood by aid of
the law of combination. A complex object, presenting a number of parts
and characteristics, arouses the response of seeing and perhaps naming
the object. This is a unitary response to a collection of stimuli, and
each of the parts or characteristics of the object participates in
arousing the response, and the linkage of each part with the response
is thus strengthened. Later, therefore, the whole identical object is
not required to arouse this same {408} response, but some of its parts
or characteristics will give the response, and they may do this even
when they are present in an object that has other and unfamiliar parts
and characteristics.
The machinery of association by similarity is the same, with the
addition of a second response, called out by the new characteristics
of the present object.
II. SUBSTITUTE RESPONSE EXPLAINED BY THE LAW OF COMBINATION
The substitute response machinery is more complicated than that of the
substitute stimulus, as it includes the latter and something more.
What that something more is will be clear if we ask ourselves why a
substitute response should ever be made. Evidently because there is
something wrong with the original response; if that were entirely
satisfactory, it would continue to be made, and there would be no room
for a substitute. The original response being unsatisfactory to the
individual, how is he to find a substitute? Only by finding some
stimulus that will arouse it. This is where trial and error come in,
consisting in a search for some extra stimulus that shall give a
satisfactory response.
Suppose now that the extra stimulus has been found which arouses a
satisfactory substitute response. The original stimulus, or the
reaction-tendency aroused by it, still continuing, participates in
arousing the substitute response, playing the part of the originally
ineffective stimulus in the conditioned reflex. Thus the original
stimulus becomes strongly linked with the substitute response.
The process of reaching a substitute response thus includes three
stages: (a) original response found unsatisfactory, (b) new stimulus
found which gives a satisfactory substitute response, (c) attachment
of the substitute response to the original stimulus.
{409}
There are two main cases under the general head of substitute
response. In one case, the substitute response is essentially an old
response, not acquired during the process of substitution, but simply
substituted, as indicated just above, for the original response to the
situation. This represents the common trial and error learning of
animals. The second case is that where the substitute response has to
be built up by combination of old responses into a higher unit.
C. Substitute Response, but not in Itself a New Response
I. Trial and error.
Our much-discussed instance of the _cat in the cage_ need not be
described again, but may simply be illustrated by a diagram.
[Illustration: Fig. 60.--How the cat learns the trick of escaping from
the cage by unlatching the door. S is the situation of being shut up
in a cage, and T is the tendency to get out. R1 is the primary
response aroused by this tendency, which response meets with failure,
not leading to the end-result of the tendency. Responses are then made
to various particular stimuli about the cage, and one of these
stimuli, the door-latch, X, gives the response R2 which leads to the
end-result. Now the response R2 was in part aroused by T, and its
pre-existing weak linkage with T is so strengthened by exercise that
T, or we may say S, comes to give the correct response without
hesitation.]
{410}
2. Learning to balance on a bicycle.
When the beginner feels the bicycle tipping to the left, he naturally
responds by leaning to the right, and even by turning the wheel to the
right. Result unsatisfactory--strained position and further tipping to
the left. As the bicyclist is about to fall, he saves himself by a
response which he has previously learned in balancing on his feet; he
extends his foot to the left, which amounts to a response to the
ground on the left as a good base of support. Now let him sometime
respond to the ground on his left by turning his wheel that way, and,
to his surprise and gratification, he finds the tipping overcome, and
his balance well maintained. The response of turning to the left,
originally made to the ground on the left (but in part to the
tipping), becomes so linked with the tipping as to be the prompt
reaction whenever tipping is felt. The diagram of this process would
be the same as for the preceding instance.
D. Substitute Response, the Response Being a Higher Motor Unit
1. The brake and clutch combination in driving an automobile.
This may serve as an instance of _simultaneous coördination_, since
the two movements which are combined into a higher unit are executed
simultaneously. The beginner in driving an automobile often has
considerable trouble in learning to release the "clutch", which,
operated by the left foot, ungears the car from the engine, and so
permits the car to be stopped without stopping the engine. The foot
brake, operated by the right foot, is comparatively easy to master,
because the necessity for stopping the car is a perfectly clear and
definite stimulus. Now, when the beginner gets a brake-stimulus, he
responds promptly with his right foot, but neglects to employ his left
foot on the clutch, because he has no effective clutch-stimulus; there
is nothing {411} in the situation that reminds him of the clutch.
Result, engine stalled, ridicule for the driver. Next time, perhaps,
he _thinks_ "clutch" when he gets the brake-stimulus, and this
thought, being itself a clutch-stimulus, arouses the clutch-response
simultaneously with the brake-response. After doing this a number of
times, the driver no longer needs the thought of the clutch as a
stimulus, for the left foot movement on the clutch has become
effectively linked with the brake-stimulus, so that any occasion that
arouses the brake-response simultaneously arouses the clutch response.
[Illustration: Fig. 61.--Combining clutch-response with
brake-response. At first, the brake-stimulus has only a weak linkage
with the clutch-response, and an extra stimulus has to be found to
secure the clutch-response. But whenever the clutch-response is made
while the brake-stimulus is acting, the weak linkage between these two
is exercised, till finally the brake-stimulus is sufficient to give
the clutch-response, along with the brake-response.]
The combination of two responses is effected by linking both to the
same stimulus; thus the two become united into a coördinated higher
motor unit.
2. The word-habit in typewriting furnishes an example of _successive
coördination_, the uniting of a sequence of movements into a higher
unit. [Footnote: See p. 324.] The beginner has to spell out {412} the
word he is writing, and make a separate response to each letter; but
when he has well mastered the letter-habits, and, still unsatisfied,
is trying for more speed, it happens that he thinks ahead while
writing the first letter of a word, and _prepares_ for the second
letter. In effect, he commences reacting to the second letter while
still writing the first. This goes further, till he anticipates the
series of letters forming a short word while still at the beginning of
the word. The letter movements are thus linked to the thought of the
word as a whole, and the word becomes an effective stimulus for
arousing the series of letter movements.
[Illustration: Fig. 62.--Learning a word-habit in typewriting. At
first, besides the stimulus of the word, "_and_" it is necessary also
to have the stimulus "_a_" in order to arouse the response of writing
a, the stimulus "_n_" in order to arouse the writing of n, and the
stimulus "_d_" in order to arouse the writing of d. Yet the stimulus
"_and_" is present all this time, and its weak linkages with the
writing movements are used and strengthened, so that finally it is
sufficient, by itself, to arouse the whole series of writing
movements.]
Many other instances of learning can be worked out in the same way,
and there seems to be no difficulty in {413} interpreting any of them
by the law of combination. Even "negative adaptation" can possibly be
interpreted as an instance of substitute response; some slight and
easy response may be substituted for the avoiding reaction or the
attentive reaction that an unimportant stimulus at first arouses,
these reactions being rather a nuisance when they are unnecessary. On
the whole, the law of combination seems to fill the bill very well. It
explains what the law of exercise left unexplained. It always brings
in the law of exercise as an ally, and, in explaining substitute
response, it brings in the law of effect, which however, as we saw
before, may be a sub-law under the law of exercise. These two, or
three laws, taken together, give an adequate analysis of the whole
process of learning.
The Law of Combination in Recall
Unitary response to multiple stimuli is important in recall as well as
in learning. The clearest case of this is afforded by "controlled
association". [Footnote: See p. 381.]
In an opposites test, the response to the stimulus word "long" is
aroused partly by this stimulus word, and partly by the "mental set"
for opposites. There are two lines of influence, converging upon the
response, "long--short" (of which only the word "short" may be
spoken): one line from the stimulus word "long", and the other from
the mental set for pairs of opposite words. The mental set for
opposites tends to arouse any pair of opposites; the word "long" tends
to arouse any previously observed group of words of which "long" is a
part. The mental set, an internal stimulus, and the stimulus word
coming from outside, converge or combine to arouse one particular
response.
The mental set for adding has previously exercised {414} linkages with
the responses composing the addition table, while the mental set for
multiplication has linkages with the responses composing the
multiplication table. When the set for adding is active, a pair of
numbers, seen or heard, together with this internal stimulus of the
mental set, arouses the response that gives the sum; but when the
multiplying set is active, the same pair of numbers gives the product
as the response. All thinking towards any goal is a similar instance
of the law of combination.
The Laws of Learning in Terms of the Neurone
We have good evidence that the brain is concerned in learning and
retention. Loss of some of the cortex through injury often brings loss
of learned reactions, and the kind of reactions lost differs with the
part of the cortex affected. Injury in the occipital lobe brings loss
of visual knowledge, and injury in the neighborhood of the auditory
sense-center brings loss of auditory knowledge.
Injury to the retina or optic nerve, occurring early in life, results
in an under-development of the cortex in the occipital lobe. The nerve
cells remain small and their dendrites few and meager, because they
have not received their normal amount of exercise through stimulation
from the eye.
Exercise, then, has the same general effect on neurones that it has on
muscles; it causes them to grow and it probably also improves their
internal condition so that they act more readily and more strongly.
The growth, in the cortex, of dendrites and of the end-brushes of
axons that interlace with the dendrites, must improve the synapses
between one neurone and another, and thus make better conduction paths
between one part of the cortex and another, and also between the
cortex and the lower sensory and motor centers.
The law of exercise has thus a very definite meaning when {415}
translated into neural terms. It means that the synapses between
stimulus and response are so improved, when traversed by nerve
currents in the making of a reaction, that nerve currents can get
across them more easily the next time.
[Illustration: Fig. 63.--The law of exercise in terms of synapse. A
nerve current is supposed to pass along this pair of neurones in the
direction of the arrow. Every time it passes, it exercises the
end-brush and dendrites at the synapse (for the "passage of a nerve
current" really means activity on the part of the neurones through
which it passes), and the after-effect of this exercise is growth of
the exercised parts, and consequent improvement of the synapse as a
linkage between one neurone and the other. Repeated exercise may
probably bring a synapse from a very loose condition to a state of
close interweaving and excellent power of transmitting the nerve
current.]
The more a synapse is used, the better synapse it becomes, and the
better linkage it provides between some stimulus and some response.
The cortex is the place where linkages are made in the process of
learning, and it is there also that forgetting, or atrophy, takes
place through disuse. Exercise makes a synapse closer, disuse lets it
relapse into a loose and poorly conducting state.
The law of combination, also, is readily translated into {416} neural
terms. The "pre-existing loose linkages" which it assumed to exist
undoubtedly do exist in the form of "association fibers" extending in
vast numbers from any one part of the cortex to many other parts.
These fibers are provided by native constitution, but probably
terminate rather loosely in the cortex until exercise has developed
them. They may be compared to telephone wires laid down in the cables
through the streets and extending into the houses, but still requiring
a little fine work to attach them properly to the telephone
instruments.
[Illustration: Fig. 64.--Diagram for the learning of the name of an
object, transformed into a neural diagram. The vocal movement of
saying the name is made in response to the auditory stimulus of
hearing the name, but when the neurone in the "speech center" is thus
made active, it takes up current also from the axon that reaches it
from the visual center, even though the synapse between this axon and
the speech neurone is far from close. This particular synapse between
the visual and the speech centers, being thus exercised, is left in an
improved condition. Each neurone in the diagram represents hundreds in
the brain, for brain activities are carried on by companies and
regiments of neurones. (Figure text: object seen, visual center name
heard, auditory center, speech center, name spoken)]
The diagrams illustrating different cases under the law of combination
can easily be perfected into neural diagrams, though, to be sure, any
diagram is ultra-simple as compared with the great number of neurones
that take part in even a simple reaction.
The reader will be curious to know now much of this neural
interpretation of our psychological laws is observed fact, and how
much speculation. Well, we cannot as yet {417} observe the brain
mechanism in actual operation--not in any detail. We have good
evidence, as already outlined, for growth of the neurones and their
branches through exercise.
[Illustration: Fig. 65.--Control, in multiplying. The visual stimulus
of two numbers in a little column, has preformed linkages both with
the adding response and with that of multiplying. But the mental set
for adding being inactive at the moment, and that for multiplying
active (because the subject means to multiply), the multiplying
response is facilitated.]
We have perfectly good evidence of the law of "unitary response to
multiple stimuli" from the physiological study of reflex action; and
we have perfectly good anatomical evidence of the convergence and
divergence of neural paths of connection, as required by the law of
combination. The association fibers extending from one part to another
of the cortex are an anatomical fact. [Footnote: See p. 56.]
Facilitation is a fact, and that means that a stimulus which could not
of itself arouse a response can coöperate with another stimulus that
has a direct connection with that response, and reinforce its effect.
In short, all the elements required for a neural law of combination
are known facts, and the only matter of doubt is whether we have built
these elements together aright in our interpretation. It is not pure
speculation, by any means.
{418}
EXERCISES
1. Outline the chapter, in the form of a list of laws and sub-laws.
2. Review the instances of learning cited in Chapters XIII-XV,
and examine whether they are covered and sufficiently accounted for
by the general laws given in the present chapter.
3. Draw diagrams, like those given in this chapter, for the simpler
cases, at least, that you have considered in question 2.
4. Show that response by analogy is important in the development
of language. Consider metaphor, for example, and slang, and the
using of an old word in a new sense (as in the case of
'rail-road').
REFERENCES
William James devoted much thought to the problem of the mechanism of
learning, habit, association, etc., and his conclusions are set forth
in several passages in his _Principles of Psychology_, 1890, Vol. I,
pp. 104-112, 554-594, and Vol. II, pp. 578-592.
Another serious consideration of the matter is given by William
McDougall in his _Physiological Psychology_, 1905, Chapters VII and
VIII.
See also Thorndike's _Educational Psychology, Briefer Course_, 1914,
Chapter VI.
On the whole subject of association, see Howard C. Warren, _A History
of the Association Psychology_, 1921.
{419}
CHAPTER XVII
PERCEPTION
MENTAL LIFE CONSISTS LARGELY IN THE DISCOVERY OF FACTS NEW TO THE
INDIVIDUAL, AND IN THE RE-DISCOVERY OF FACTS PREVIOUSLY OBSERVED
You will remember the case of John Doe, who was brought before us for
judgment on his behavior, as to how far it was native and how far
acquired. We have since that time been occupied in hearing evidence on
the case, and after mature consideration have reached a decision which
we may formulate as follows: that this man's behavior is primarily
instinctive or native, but that new attachments of stimulus and
response, and new combinations of responses, acquired in the process
of learning, have furnished him with such an assortment of habits and
skilled acts of all sorts that we can scarcely identify any longer the
native reactions out of which his whole behavior is built. That
decision being reached, we are still not ready to turn the prisoner
loose, but wish to keep him under observation for a while longer, in
order to see what use he makes of this vast stock of native and
acquired reactions. We wish to know how an individual, so equipped,
behaves from day to day, and meets the exigencies of life. Such, in
brief, is the task we have still before us.
Accordingly, one fine morning we enter our prisoner's sleeping
quarters, and find him, for once, making no use of his acquired
reactions, as far as we can see, and utilizing but a small fraction of
his native reactions. He is, in short, asleep. We ring a bell, and he
stirs uneasily. We {420} ring again, and he opens his eyes sleepily
upon the bell, then spies us and sits bolt upright in bed. "Well, what
. . ." He throws into action a part of his rather colorful vocabulary.
He evidently sees our intrusion in an unfavorable light at first, but
soon relaxes a little and "supposes he must be late for breakfast".
Seeing our stenographer taking down his remarks, he is puzzled for a
moment, then breaks into a loud laugh, and cries out, "Oh! This is
some more psychology. Well, go as far as you like. It must have been
your bell I heard in my dream just now, when I thought I saw a lot of
cannibals beating the tom-tom". Having now obtained sufficient data
for quite a lengthy discussion, we retire to our staff room and
deliberate upon these manifestations.
"The man perceives", we agree. "By the use of his eyes and ears he
discovered facts, and interpreted them in the light of his previous
experience. In knowing the facts, he also got adjusted to them and
governed his actions by them. But notice--a curious thing--how his
perception of the facts progressed by stages from the vague and
erroneous to the correct and precise. Before he was fully awake, he
mistook the bell for a tom-tom; then, more fully aroused, he knew the
bell. Ourselves he first saw as mere wanton intruders, then as
cheerful friends who wished him no ill; finally he saw us in our true
character as investigators of his behavior."
Following our man through the day's work and recreation, we find a
large share of his mental activity to consist in the perception of
facts. We find that he makes use of the facts, adjusting himself to
them and also shaping them to suit himself. His actions are governed
by the facts perceived, at the same time that they are governed by his
own desires. Ascertaining how the facts stand, he takes a hand and
manipulates them. He is constantly coming to know {421} fresh facts,
and constantly doing something new with them. His life is a voyage of
discovery, and at the same time a career of invention.
Discovery and invention!--high-sounding words, still they are
applicable to everyday life. The facts observed may not be absolutely
new, but at least they have always to be verified afresh, since action
needs always to take account of present reality. The invention may be
very limited in scope, but seldom does an hour pass that does not call
for doing something a little out of the ordinary, so as to escape from
a fresh trap or pluck fruit from a newly discovered bough. All of our
remaining chapters might, with a little forcing, be pigeonholed under
these two great heads. Discovery takes its start with the child's
instinctive exploratory activity, and invention with his manipulation,
and these two tendencies, perhaps at bottom one, remain closely
interlinked throughout.
Some Definitions
_Perception_ is the culmination of the process of discovery. Discovery
usually requires exploration, a search for facts; and it requires
attention, which amounts to finding the facts or getting them
effectively presented; and perception then consists in knowing the
presented facts.
When the facts are presented to the senses, we speak of "sense
perception". If they are presented to the eye, we speak of visual
perception; if to the ear, of auditory perception, etc. But when we
speak of a fact as being "presented" to the eye or ear, we do not
necessarily mean that it is directly and completely presented; it may
only be indicated. We may have before the eyes simply a _sign_ of some
fact, but perceive the fact which is the _meaning_ of the sign. We
look out of the window and "see it is wet to-day", though wetness is
something to be felt rather than seen; {422} having previously
observed how wet ground looks, we now respond promptly to the visual
appearance by knowing the indicated state of affairs. In the same way,
we say that we "hear the street car", though a street car, we must
admit, is not essentially a noise. What we hear, in strictness, is a
noise, but we respond to the noise by perceiving the presence of the
car. Responding to a stimulus presented to one sense by perceiving a
fact which could only be directly presented to another sense is
exemplified also by such common expressions as that the stone "looks
heavy", or that the bell "sounds cracked". or that the jar of fruit
"smells sour". Sense perception, then, is responding to a stimulus by
knowing some fact indicated by it either directly or indirectly.
Perception that is not sense perception occurs when the fact perceived
is not even indirectly presented to the senses at the moment. The fact
is then presented by recall; yet the fact in question is not recalled.
Recall not only gives you facts previously perceived, but may provide
the data, the stimulus, for fresh perception. Putting together two
recalled facts, you may perceive a further fact not previously known.
Remembering that you took your umbrella to the office this morning in
the rain, that it was fine when you left the office, and that you
certainly did not have the umbrella when you reached home, you
perceive that you must have left it at the office. Reading in the
paper of preparations for another polar expedition, and remembering
that both poles have already been discovered, you perceive that there
is something more in polar exploration than the mere race for the
pole. Perception of this sort amounts to "reasoning", and will be
fully considered in another chapter, while here we shall focus our
attention on sense perception.
{423}
The Difference Between Perception and Sensation
If sense perception is a response to a sensory stimulus, so is
sensation, and the question arises whether there is any genuine
difference between these two. In the instance of "hearing the street
car", the difference is fairly obvious; hearing the noise is
sensation, while knowing the street car to be there is perception.
Sensation is the first response aroused by a stimulus, or at least the
first response that is conscious. Perception is a second response,
following the sensation, and being properly a direct response to the
sensation, and only an indirect response to the physical stimulus. The
chain of events is: stimulus, response of the sense organ and sensory
nerve, first cortical response which is sensation, second cortical
response which is perception.
Conscious sensation is the response of the part of the cortex that
first receives the nerve current from the sense organ stimulated, the
response of the "sensory area" for the particular sense stimulated.
When the eye is stimulated, the nerve current first reaches a small
portion of the occipital lobe, called the visual sensory area. Without
that area there is no visual sensation. When the ear is stimulated,
the conscious sensation is the response of a small portion of the
temporal lobe called the auditory sensory area, and without this area
there is no auditory sensation. But the presence of the visual sensory
area is not enough to give the visual perception of facts, nor is the
presence of the auditory sensory area enough to give auditory
perception. The cortical regions _adjacent_ to the sensory areas are
necessary for perception; if they are destroyed, the individual may
still see, but not know the objects seen; or may still hear, but not
recognize the words or tunes that he hears. If the cortical area
destroyed is in the parietal {424} lobe, adjacent to the sensory area
for the cutaneous and kinesthetic senses, he may still "feel" objects,
but without being able to distinguish an apple from a lump of coal, or
a folded newspaper from a tin pail.
Sense perception, then, is a response of areas adjacent to the sensory
areas, and this response is aroused by nerve currents coming along
"association fibers" from the sensory areas which are first aroused
from the sense organs.
The whole chain of events, from the time the stimulus reaches the
sense organ to the time the fact is perceived, occupies only a fifth
or even a tenth of a second in simple cases, and the interval between
the beginning of the sensation to the beginning of the perception is
not over a twentieth when the fact is easily perceived. Since the
sensation usually lasts for longer than this, it overlaps the
perception in time, and the two conscious responses are so _blended_
that it is difficult or impossible for introspection to separate them.
But when an unusual fact is presented, perception may lag, though
sensation occurs promptly. We may be baffled and confused for an
instant, and have sensation without any definite perception; or, more
often, we make a rapid series of _trial and error perceptions_. In one
instance, a noise was first heard as distant thunder, and then,
correctly, as somebody walking on the floor above. In another case, a
faint sound was first taken for a bird singing, then for a distant
locomotive whistle, and finally for what it was, the tinny noise of a
piece of metal carried in the hand and brushing against the overcoat
as the person walked; this series occupied not over five seconds. On
touching an object in the dark, you may feel it as one thing and
another till some response is aroused that fits the known situation
and so satisfies you. Such trial and error perception can be observed
very frequently if one is on the watch for {425} psychological
curiosities; and it justifies the distinction between sensation and
perception, since the sensation remains virtually unchanged while
perception changes.
Another sort of shifting perception is seen in looking steadily at the
"ambiguous figures" which were considered in the chapter on attention,
the cube, staircase, and others; and the "dot figures" belong here as
well. [Footnote: See p. 252.] In these cases the stimulus arouses two
or more different perceptions, alternately, while the sensation
remains almost or quite unchanged.
Perception and Image
The experiment with ambiguous figures also gives an answer to the
question whether perception consists in the addition of recalled
memory images to the sensations aroused by the present stimulus. If
that were so, you should, when you see the upper side of the flight of
stairs, see them as wooden stairs or stone stairs, as carpeted or
varnished, with shadows on them such as appear on a real flight of
stairs, with a railing, or with some other addition of a similar
nature; and, when the appearance changes to that of the under side of
a flight of stairs, the colors, shadows, etc., should change as well.
The usual report is that no such addition can be detected, and that
the subject sees no filling-in of the picture, but simply the bare
lines--only that they seem at one moment to be the bare outline of the
upper side, and at another moment an equally bare outline of the lower
side, of a flight of stairs.
So again, when you "hear the street car", you do not ordinarily, to
judge from the reports of people who have been asked, get any visual
or kinesthetic image of the car, but you simply know the car is there.
You will quite {426} possibly get some such image, if you _dwell_ on
the fact of the car's being there, just as some persons, in talking to
a friend over the telephone, have a visual image of the friend. There
is no reason why such images should not be aroused, but the question
is whether they are essential to perception of the fact, and whether
they occur before or after the fact is perceived. Often they do not
occur, and often, when they do occur, they follow the perception of
the fact, being aroused by that perception and not constituting it.
Sometimes images are certainly aroused during the perception of a
fact, and, blending with the present rather vague sensation, add color
and filling to the picture.
Here is an instance of this which I once observed in myself, in spite
of the infrequency of my visual images. Approaching a house through a
wide field one winter night, and seeing a lamp shining out of a window
towards me, I seemed to see the yellowish light touching the high
spots in the grass around. I was surprised that the lamp should carry
so far, and the next instant saw that the light spots on the ground
were small patches of snow, lighted only from the clouded sky; and at
this the yellow tinge of the spots vanished. I must have read the
yellow color into them to fit the lamplight. The yellow was an image
blending with the actual sensation. Colors tacked on to a seen object
in this way are sometimes called "memory colors".
When this instance is considered carefully, however, it does not by
any means indicate that the image produced the perception. I responded
to the pair of stimuli--lamp shining towards me and light spots around
me--by perceiving the spots as lighted by the lamp; and the color
followed suit. I next saw the spots as snow, and the color vanished.
It was a case of trial and error perception, with color images
conforming to the perception.
Perception does not essentially consist in the recall of {427} images,
but is a different sort of response--what sort, we have still to
consider.
Perception and Motor Reaction
Possibly, we may surmise, perception is a motor response, completely
executed or perhaps merely incipient, or at least a readiness for a
certain motor response. This guess is not quite so wild as our
customary sharp distinction between knowing and doing might lead us to
think. When we say that reacting to a thing in a motor way is quite
different from merely seeing the thing, we forget how likely the child
is to do something with any object as soon as he sees what it is. We
forget also how common it is for a person, in silently reading a
word--which is perceiving the word--to whisper it or at least move his
lips. To be sure, persons who read a great deal usually get over this
habit, as the child more and more inhibits his motor response to many
seen objects. But may it not be that the motor response is simply
reduced to a minimum? Or, still better, may it not be that perceiving
an object amounts to _getting ready_ to do something with it? May not
seeing a word always be a getting ready to say it, even if no actual
movement of the vocal organs occurs? May not seeing an orange consist
in getting ready to take it, peel it, and eat it? May not perceiving
our friend amount to the same thing as getting ready to behave in a
friendly manner, and perceiving our enemy amount to the same thing as
getting on our guard against him? According to this view, perception
would be a response that adjusted the perceiver to the fact perceived,
and made him ready to do something appropriate.
In spite of the attractiveness of this theory of perception, it is
probably not the real essence of the matter. Just as perception may
change while sensation remains the same, so there may be a hesitation
between two motor responses {428} to an object, without any change in
the way it is perceived; and just as a block may occur between
sensation and perception, so also may one occur between perception of
a fact and the motor response. In other words, perception of a fact
may not spell complete readiness to act upon it. The best example of
this is afforded again by cases of localized brain injuries.
It happens, in motor aphasia, that the subject hears and understands a
spoken word--fully perceives it--and yet cannot pronounce it himself.
And at that, there need be no paralysis of the speech organs. The
brain injury has affected the motor speech-coördinating machinery, and
deprived the individual of the power to get ready for speaking a word,
even though he perceives it.
Analogous disabilities occur in respect to other movements. It may
happen, through injury somewhere near the motor area, though not
precisely in that area, that one who clearly perceives a seen object
is still quite incapable of handling it. He knows the object, and he
knows in an abstract way what to do with it, but how to go about it he
cannot remember. This type of disturbance is called "motor apraxia",
and, like motor aphasia, it proves that there is a preparation that
follows perception and still precedes actual movement. Paralysis of
the motor area is different; then, the subject both perceives the
object, and gets all ready to act upon it; only, the movement does not
occur.
The truth seems to be that a series of four responses occurs in the
brain, in the process of making a skilled movement dealing with a
perceived object. First, sensation; second, perception of the object;
third, coördinating preparation for the act; and fourth, execution of
the act by the motor area arousing the lower motor centers and through
them the muscles. The first response is like receiving signals {429}
or code messages; the second deciphers the messages and knows the
state of affairs; the third plans action; and the fourth sends out
orders to the agents that perform the action.
The distinction between perception and preparation for action is
sometimes rather difficult to draw. The twelve o'clock whistle means
time to drop your tools, and it is hard to draw a line between knowing
the fact and beginning the act. On the other hand, when my watch tells
me the noon hour is almost over, some little time may be required
before I get into motion. Where there is no block or inhibition, the
chain of responses runs off with such speed as to seem a single
response. But a block may occur at any one of several places. It may
check the actual movement, as in the "delayed reaction", [Footnote:
See p. 76.] and in cases where we itch to do something yet check
ourselves. Here the preparation occurs, but the execution is checked.
Sometimes the block occurs between perception and preparation, when we
know a fact but find nothing to do about it or hesitate between two
ways of acting. Sometimes, also, the block occurs between sensation
and perception; a sudden loud noise will sometimes throw a person into
a momentary state of confusion during which he is unable to recognize
the noise.
Blocking of response at different stages can be illustrated very well
in the case of anger. The irritating stimulus gives a prompt fighting
reaction, unless checked at some stage. When the check prevents me
from actually striking the offending person, but leaves me clenching
my fist and gnashing my teeth, the chain of responses has evidently
gone as far as readiness for action, and been blocked between that
stage and the stage of execution. Probably the inhibitory influence
here is anticipation of bad consequences. The block may occur one
stage further back, when I say to myself that {430} I mustn't let
myself get "all riled up" since it will spoil my morning's work; here,
instead of substituting the clenched fist for actual fighting, I
substitute a bored or contemptuous attitude for the pugnacious
attitude. All this time I still am conscious of the offense done me.
But suppose something leads me to try to look at the other person's
behavior from his own point of view--then I perceive it in a different
light, and it may no longer appear a personal offense to myself. I
here get a substitute perception.
The process of blocking and substituting is the same process that we
have seen in trial and error.[Footnote: See p. 408.] The response
proving unsatisfactory, or promising to be unsatisfactory, is checked
and a substitute response found. Other elements in the situation get a
chance to exert their influence on the reaction. If perception of a
fact were absolutely the same as preparing a motor act, we could not
look over the situation, perceiving one fact after another, and
letting our adjustment for action depend on the total situation
instead of on the separate facts successively observed; nor could we
perceive one fact while preparing the motor response to another fact,
as is actually done in telegraphy, typewriting, reading aloud, and
many other sorts of skilled action. In reading aloud, the eyes on the
page keep well ahead of the voice; while one word is being pronounced,
the next word is being prepared for pronouncing, and words still
further ahead are in process of being perceived.
We conclude, accordingly, that perception of an object is not
absolutely the same thing as motor response to the object, nor even as
motor readiness to respond, although the transition from perception to
motor readiness may be so quick that the whole reaction seems a unit.
In reality, perception of the object precedes the motor adjustment,
and is one factor in determining that adjustment.
{431}
What Sort of Response, Then, Is Perception?
We can say this, that perception is knowing the fact, as distinguished
from readiness to act. We can say that perception is an adjustment to
facts as they are, while motor adjustment is a preparation for
changing the facts. Perception does not alter the facts, but takes
them as they are; movement alters the facts or produces new facts. We
can say that perception comes in between sensation and motor
preparation. But none of these statements is quite enough to satisfy
us, if we wish to know something of the machinery of perception. What
is the stimulus in perception, and what is the nature of the response?
It takes a collection of stimuli to arouse a perception. This
collection is at the same time a selection from among the whole mass
of sensory stimuli acting at any moment on the individual. Perception
is thus a fine example both of the "law of selection" and of the "law
of combination". [Footnote: See pp. 256, 263.] Perception is at once a
_combining_ response and an _isolating_ response.
We perceive a face--that means that we take the face as a unit, or
make a unitary response to the multiple stimuli coming from the face.
At the same time, in perceiving the face, we isolate it from its
background, or disregard the numerous other stimuli that are
simultaneously acting upon us. If we proceed to examine the face in
detail, we may isolate the nose and perceive that as a whole. We might
isolate still further and perceive a freckle on the nose, taking that
as a whole, or even observing separately its location, diameter, depth
of pigmentation, etc. Even if we went so far as to observe a single
speck of dust on the skin, in which case isolation would about reach
its maximum, combination would still stay in the game, for we should
either note {432} the location of the speck--which would involve
relating it to some part of the face--or we should contrast it with
the color of the skin, or in some similar way take the single stimulus
in relation with other present stimuli. Perception is always a unitary
response to an isolated assemblage of stimuli.
Consider these two opposite extremes: taking in the general effect of
the view from a mountain top, and perceiving the prick of a pin. In
the first case, combination is very much in evidence, but where is the
isolation? There is isolation, since internal bodily sensations, and
very likely auditory and olfactory sensations as well, are present but
do not enter into the view. In the case of the pin prick, isolation is
evident, but where does combination come in? It would not come into
the mere reflex of pulling the hand away, but perceiving the pin means
something more than reflex action. It means locating the sensation, or
noticing its quality or duration or something of that sort, and so
contrasting it with other sensations or relating it to them in some
way. To perceive one stimulus as related to another is to respond to
both together.
But in describing perception as a unitary response to an isolated
assemblage of stimuli, we have not differentiated it from a motor
response, for that, too, is often aroused by a few (or many) stimuli
acting together. What more can we say? In neural terms, we can only
repeat what was said before, that perception is the next response
after sensation, being a direct response to a certain combination of
sensations, and being in its turn the stimulus, or part of the
stimulus, that arouses a motor adjustment, as it may also be the
stimulus to recall of previously observed facts. In more psychological
terms, we can say that sense perception is closely bound up with
sensation, so that we seem to see the fact, or hear it, etc.; we
perceive it as present to the {433} senses, rather than as thought of
or as anticipated. Motor readiness is anticipatory, perception
definitely objective. Motor readiness is an adjustment for something
yet to be, while perception is an adjustment to something already
present.
Practised Perception
A fact perceived for the first time must needs be attended to, in
order that it may be perceived. That is, the first and original
perception of a fact is a highly conscious response. But the
perception of a fact, like any other form of response, becomes easy
with practice; the linkage of stimulus and response becomes stronger
and stronger, till finally the stimulus arouses the perceptive
response almost automatically. The familiar fact is perceived without
receiving close attention, or even without receiving any attention.
While your attention is absorbed in reading or thinking, you may
respond to the sight of the flower in a vase on your table by knowing
it to be there, you may respond to the noise of the passing street car
by knowing what that is, and you may respond to the contact of your
foot with the leg of the chair by dimly knowing what that object is. A
great deal of this inattentive perception of familiar facts is always
going on. Aside from sensation and from some of the reflexes, the
perception of familiar facts is the most practised and the easiest of
all responses.
The laws and sub-laws of learning apply perfectly to practised
perception. The more frequently, the more recently, and the more
intensely a given fact has been perceived, the more readily is it
perceived again. The more a given fact is in line with the mental set
of the moment, the more readily is it perceived. Sometimes it is so
readily perceived that we think we see it when it isn't there. If you
are hunting for a lost knife, anything remotely resembling {434} a
knife will catch your eye and for an instant be perceived as the
missing object.
The principle of _substitute stimulus_ applies remarkably well to
practised perception. The first time you perceive an object, you
observe it attentively, and expose your perceptive apparatus to the
whole collection of stimuli that the object sends your way. The next
time you need not observe it so attentively, for you make the same
perceptive response to a _part_ of the original collection of stimuli.
The response originally aroused by the whole collection of stimuli is
later aroused by a fraction of this collection. The stimulus may be
_reduced_ considerably, and still arouse the perception of the same
fact. A child is making the acquaintance of the dog. The dog barks,
and the child watches the performance. He not only sees the dog, and
hears the noise, but he _sees_ the dog _bark_, and _hears_ the dog
_bark_. This original perception is a unitary response to the
combination of sight and sound. Thereafter he does not require both
stimuli at once, but, when he hears this noise, he perceives the dog
barking, and when he sees the dog he sees an object that can bark. In
the same way, a thousand objects which furnish stimuli to more than
one of the senses are perceived as units, and, later, need only act on
a single sense to be known.
The stimulus, instead of being reduced, may be _modified_, and still
arouse the same perception as before. A face appears in the baby's
field of view, but away across the room so that it is a very small
object, visually. The face approaches and gradually becomes a larger
visual object, and the light and shadow upon it change from moment to
moment, but it remains nearly enough the same to arouse essentially
the same perception in the child. He comes to know the face at various
distances and angles and under various lights.
{435}
Again, the child holds a block in his hands, and looks at it square
on, so that it is really a rectangle in his field of view. He turns it
slightly, and now it is no longer visually a rectangle, but an oblique
parallelogram. But the change is not enough to abolish the first
perception; he sees it as the same object as before. By dint of many
such experiences, we see a book cover or a door as a rectangle, no
matter at what angle we may view it, and we know a circle for a circle
even though at most angles it is really an ellipse in the field of
view. A large share of practised perceptions belong under the head of
"response by analogy",[Footnote: See p. 406.] since they consist in
making the same response to the present stimulus that has previously
been made to a similar but not identical stimulus. If every modified
stimulus gave a new and different perception, it would be a slow job
getting acquainted with the world. A thing is never twice the same, as
a collection of stimuli, and yet, within wide limits, it is always
perceived as the same thing.
Corrected Perception
Response by analogy, however, often leads us astray, in making us
perceive a new object as essentially the same as something already
familiar. First impressions of a new object or acquaintance often need
revision, because they do not work well. They do not work well because
they are rough and ready, taking the object in the lump, with scant
attention to details which may prove to be important. It is easy to
follow the law of combination and respond to a whole collection of
stimuli, but to break up the collection and isolate out of it a
smaller collection to respond to--that is something we will not do
unless forced to it. Isolation and discrimination are uphill work.
When they occur, it is {436} because the rough and ready response has
proved unsatisfactory,
_Substitute response_ is the big factor in corrected perception, as
substitute stimulus is in practised perception. When our first
perception of an object gets us into difficulties, then we are forced
to attend more closely and find something in the object that can serve
as the stimulus to a better response. This is the process by which we
isolate, analyze, discriminate.
Our old friend, the white rat, learned to enter a door only if it bore
a yellow sign. [Footnote: See p. 304.] It was uphill work for him,
hundreds of trials being required before the discriminating response
was established; but he learned it finally. At the outset, a door was
a door to the rat, and responded to as such, without regard to the
sign. Whenever he entered a door without the sign, he got a shock, and
scurried back; and before venturing again he looked all around,
seeking, we may say, a stimulus to guide him; incidentally, he looked
at the yellow disk, and this stimulus, though inconspicuous and feeble
to a rat, finally got linked up with the entering response. The
response of first finding and then following the sign had been
substituted for the original response of simply entering.
In the same way the newly hatched chick, which at first pecks at all
small objects, caterpillars included, learns to discriminate against
caterpillars. In a practical sense, the chick, like the rat, learns to
distinguish between stimuli that at first aroused the same response.
It is in the same way that the human being is driven to discriminate
and attend to details. He is brought to a halt by the poor results of
his first rough and ready perception, scans the situation, isolates
some detail and, finding response to this detail to bring satisfactory
results, substitutes response to this {437} detail for his first
undiscriminating response to the whole object.
The child at first treats gloves as alike, whether rights or lefts,
but thus gets into trouble, and is driven to look at them more sharply
till he perceives the special characteristics of rights and lefts. He
could not describe the difference, to be sure, but he sees it well
enough for his purposes. If you ask an older person to describe this
difference, and rally him on his inability to do so, he is thus driven
to lay them side by side and study out the difference still more
precisely.
The average non-mechanical person, on acquiring an automobile, takes
it as a gift of the gods, a big total thing, simply to sit in and go.
He soon learns certain parts that he must deal with, but most of the
works remain a mystery to him. Then something goes wrong, and he gets
out to look. "What do you suppose this thing is here? I never noticed
it before". Tire trouble teaches him about wheels, engine trouble
leads him to know the engine, ignition trouble may lead him to notice
certain wires and binding-posts that were too inconspicuous at first
to attract his attention. A car becomes to him a thing with a hundred
well-known parts, instead of just one big totality.
Blocked response, closer examination, new stimulus isolated that gives
satisfactory response--such is, typically, the process of analytic
perception.
Sensory Data Serving as Signs of Various Sorts of Fact
Among facts perceived, we may list things and events, and their
qualities and relations. Under "things" we here include persons and
animals and everything that would ordinarily be called an "object".
Under "events", we include movement, change and happenings of all
sorts. Under {438} "qualities" we may include everything that can be
discovered in a thing or event taken by itself, and under "relations"
anything that can be discovered by comparing or contrasting two things
or events. The "groups" that we have several times spoken of as being
observed would here be included under "things"; but the strict logic
of the whole classification is not a matter of importance, as the only
object in view is to call attention to the great variety of facts that
are perceived.
Now the question arises, by what signs or indications these various
facts are perceived. Often, as we have seen, the fact is by no means
fully presented to the senses, and often it is far from easy for the
perceiver to tell on what signs the perception depends. He knows the
fact, but how he knows it he cannot tell. A large part of the very
extensive experimental investigation of perception has been concerned
with this problem of ferreting out the signs on which the various
perceptions are based, the precise stimuli to which the perceptions
respond.
For example, we can examine objects by feeling of them with a stick
held in the hand, and thus perceive their roughness or smoothness; but
how do we sense these facts? It seems to us as if we felt them with
the end of the stick, but that is absurd, since there are no sense
organs in the stick. It must be that we perceive the roughness by
means of sensations arising in the hand and arm, but to identify these
sensations is a much harder task than to discover the objective fact
of roughness.
Again, we distinguish the tones of two musical instruments by aid of
their overtones, but elaborate experiments were required to prove
this, since ordinarily we do not distinguish the overtones, and could
simply say that the instruments sounded differently, and let it go at
that.
Once more, consider our ability to perceive time intervals; {439} and
to distinguish an interval of a second from one of a second and a
quarter. How in the world can any one perceive time? Time is no force
that could conceivably act as a stimulus to a sense organ. It must be
some change or process that is the stimulus and that serves as the
indication of duration. Most likely, it is some muscular or internal
bodily change, but none of the more precise suggestions that have been
offered square with all the facts. It cannot be the movements of
breathing that give us our perception of time, for we can hold our
breath and still distinguish one short interval from another. It
cannot be the heart beat, for we can beat time in a rhythm that cuts
across the rate of the heart beat. When a singer is accompanying
himself on the piano, keeping good time in spite of the fact that the
notes are uneven in length, and meanwhile using his feet on the
pedals, what has he got left to beat time with? No one has located the
stimulus to which accurate time perception responds, though, in a
general way, we are pretty sure that change of one sort or another is
the datum. With longer intervals, from a minute to several hours, the
sign of duration is probably the amount happening in the interval, or
else such progressive bodily changes as hunger and fatigue.
The Perception of Space
Stimuli for the perception of location are provided by all the senses.
We perceive a taste as in the mouth, thirst as in the throat, hunger
pangs as in the stomach. To a familiar odor we may respond by knowing
the odorous substance to be close at hand. To stimulation of the
semi-circular canals we respond by knowing the direction in which we
are being turned.
We respond to sounds by knowing the direction from which they come,
and the distance from which they come; {440} but it must be confessed
that we are liable to gross errors here. To perceive the distance of
the sounding body we have to be familiar with the sound at various
distances, and our perception of distance is based on this knowledge.
As to the direction of sound, experiment has proved that we do little
more than distinguish between right and left; we are all at sea in
attempting to distinguish front from back or up from down. Apparently
the only datum we have to go by is the different stimulation given the
two ears according as the sound comes from the right or left.
The remaining senses, the cutaneous, the kinesthetic and the visual,
afford much fuller data for the perception of spatial facts. Movements
of the limbs are perceived quite accurately as to direction and
extent.
A cutaneous stimulus is located with fair exactness, though much less
exactly on such regions as the back than on the hands or lips. If you
were asked how you distinguished one point from another on the back of
the hand, you could only answer that they felt different; and if you
were further asked whether a pencil point applied to the two points of
the skin did not feel the same, you would have to acknowledge that it
did feel the same, except that it was felt in a different place. In
other words, you would not be able to identify the exact data on which
your perception of cutaneous position is based. Science has done no
better, but has simply given the name of "local sign" to the
unanalyzed sensory datum that gives a knowledge of the point
stimulated.
In handling an object, as also in walking and many other movements,
the cutaneous and kinesthetic senses are stimulated together, and
between them furnish data for the perception of many spatial facts,
such as the shape of an object examined by the hand. The spherical
shape is certainly better perceived by this combination of tactile and
kinesthetic {441} sensations than by vision, and the same is probably
true of many similar spatial facts. That is, when we see a round ball,
the visual stimulus is a substitute for the tactile and cutaneous
stimuli that originally had most to do with arousing this perception.
In part by this route of the substitute stimulus, the sense of vision
comes to arouse almost all sorts of spatial perceptions. Of itself,
the retina has "local sign" since we can tell where in the field of
view a seen object is, i.e., in what direction it is from us. This
visual perception of location is so much more exact than the cutaneous
or kinesthetic that it cannot possibly be derived from them; and the
same is true of the visual perception of difference in length, which
is one of the most accurate forms of perception. The retina must of
itself afford very complete stimuli for the perception of location and
size, as far as these are confined to the two dimensions, up-down and
right-left. But, when you stop to think, it seems impossible that the
retina should afford any data for perceiving distance in the
front-back dimension.
The retina is a screen, and the stimulus that it gets from the world
outside is like a picture cast upon a screen. The picture has the
right-left and up-down dimensions, but no front-back dimension. How,
then, does it come about, as it certainly does, that we perceive by
aid of the eye the distance of objects from us, and the solidity and
relief of objects? This problem in visual perception has received much
attention and been carried to a satisfactory solution.
Consider, first, what stimuli indicative of distance and relief could
affect a single motionless eye. The picture on the retina could then
be duplicated by a painter on canvas, and the signs of distance
available would be the same in the two cases. The painter uses
foreshortening, making a man in the picture small in proportion to his
distance away; {442} and in the same way, when any familiar object
casts a small picture on the retina, we perceive the object, not as
diminished in size, but as far away. The painter colors his near hills
green, his distant ones blue, and washes out all detail in the
latter--"aërial perspective", he calls this. His distant hill peeks
from behind his nearer one, being partially covered by it. His shadows
fall in a way to indicate the relief of the landscape. These signs of
distance also affect the single resting eye and are responded to by
appropriate spatial perceptions.
Now let the single eye move, with the head, from side to side: an
index of the distance of objects is thus obtained, additional to all
the painter has at his disposal, for the distant objects in the field
of view now seem to move with the eye, while the nearer objects slide
in the opposite direction. How much this sign is ordinarily made use
of in perceiving distance is not known; it is believed not to be used
very much, and yet it is the most delicate of all the signs of
distance. The reason why it may not be much used by two-eyed people is
that another index almost as delicate and handier to use is afforded
by binocular vision.
When both eyes are open, we have a sign of distance that the painter
does not use, though it is used in stereoscope slides. The right and
left eyes get somewhat different views of the same solid object, the
right eye seeing a little further around the object to the right, and
the left eye to the left. The disparity between the two retinal
images, due to the different angles at which they view the object, is
greatest when the object is close at hand, and diminishes to
practically zero when it is a few hundred feet away. This disparity
between the two retinal images is responded to by perception of the
distance and relief of the object.
It will be recalled [Footnote: See pp. 253-254.] that when two utterly
inconsistent {443} views are presented to the two eyes, as a red field
to one and a green field to the other, the visual apparatus balks and
refuses to see more than one at a time--the binocular rivalry
phenomenon. But when the disparate views are such as are presented to
the two eyes by the same solid object, the visual apparatus (following
the law of combination) responds to the double stimulation by getting
a single view of an object in three dimensions.
Esthetic Perception
Beauty, humor, pathos and sublimity can be perceived by the senses,
though we might debate a long time over the question whether these
characteristics are really objective, or merely our own feelings
aroused by the objects, and then projected into them. However that may
be, there is no doubt that the ability to make these responses is
something that can be trained, and that some people are blind and deaf
to beauty and humor that other people clearly perceive. Many a one
fails to see the point of a joke, or is unable to find any humor in
the situation, which are clearly perceived by another. Many a one sees
only a sign of rain in a great bank of clouds, only a weary climb in
the looming mountain.
"A primrose by the river's brim
A yellow primrose was to him.
And it was nothing more."
It would not be quite fair to describe such a one as lacking in
feeling; he probably has, on sufficient stimulus, the same feelings as
another man, and it would be more exact to say that he is lacking in
perception of certain qualities and relations. He probably tends, by
nature and training, to practical rather than esthetic perception. To
see any {444} beauty in a new style of music or painting, or to sense
the humor in a new form of humorous writing, you need to be initiated,
to be trained in observing the precise qualities and relations that
are depended on for the esthetic effect. A complex situation presents
almost an unlimited range of facts that may be perceived; no one
perceives them all, and which he shall perceive depends on his nature
and training, as well as on his attitude or mental set at the moment
when the situation is presented.
Psychology has not by any means been idle in this field of esthetics;
it has developed experimental methods for determining the preferences
of individuals and of social groups. But it must be confessed that the
results offer little that can be succinctly summarized.
One curious result is that even the very simplest objects can produce
an esthetic effect. You would scarcely suppose, for example, that a
mere rectangle could produce any esthetic effect, or that it would
make any difference what exact proportions the rectangle possessed;
and yet it is found that some rectangles are preferred to others, and
that the popular choice falls upon what the art theorists have long
known as the "golden section", a rectangle with a width about
sixty-two per cent, of its length. Also, however much you may like
symmetry, you would scarcely suppose that it could make much
difference where, on a horizontal line, a little cross line should be
erected; and yet nearly every one, on being tested, will agree that
the middle is the best point. These are merely a couple of sample
results from the numerous studies in this field.
Social Perception
By the senses we perceive the motives and intentions of other people,
their sincerity, goodness, intelligence, and {445} many other traits.
We see them angry or bored, amused, full of energy. To be sure, none
of these human characteristics is directly and fully sensed, but that
is the case also with many characteristics of inanimate objects which,
nevertheless, we perceive by aid of the senses. We perceive anger or
sincerity in much the same way that we perceive moisture or smoothness
by the eye. To experience the anger of another person is a complex
experience, but a single element from this experience may come to
serve as the sign of the whole condition. A good share of the child's
undirected education consists in learning to perceive the intentions
and characteristics of other people by aid of little signs. He learns
to read the signs of the weather in the family circle, and he learns
in some measure to be a judge of men.
I once saw an instructive little incident, in which an older boy
suddenly grabbed the cap from a little boy's head, and held it out to
the driver of a passing automobile, as if giving it to him. The man
saw the joke, and drove on laughing, but the little boy took it
seriously and was quite worried for fear the man would carry off his
cap. An older child would have "seen into" the situation readily; he
could not have been teased in that way. Many social situations which
are "all Greek" to a little child are understood readily by an older
person.
It would be very valuable if psychology could succeed in analyzing out
the signs by which such a trait as intelligence or "will power" is
perceived, so as to reduce such perception to a science; but it is
very doubtful if this can be done. Some persons who probably have
themselves a keen perception of such traits have put forward systems,
based upon the shape of the face, etc. They probably think they
perceive human traits according to their systems, but the systems fail
in other hands, and are undoubtedly {446} fallacious. No good judge of
character really goes by the shape of the face; he goes by little
behavior signs which he has not analyzed out, and therefore cannot
explain to another person.
You can tell very little regarding a person's intelligence from his
photograph. This has now been pretty well established. Photographs of
persons of various degrees of intelligence are placed before those who
are reputed to be good judges, and their estimates compared with the
test ratings, and there is no correspondence. You might just as well
look at the back of the photograph as at the front.
Even with the person before you, you are likely to commit great
errors. This sort of incident has happened. A young woman is brought
before the court for delinquency, and the psychologist who has tested
her testifies that she is of low intelligence. But the young woman is
good-looking and graceful in her speech and manners, and so impresses
the judge that he dismisses as "absurd" the notion of her being
feeble-minded. He sets her free, on which she promptly gets into
trouble again. Apparently the only way to perceive intelligence is to
see a person in action, preferably under standard conditions, where
his performance can be measured; that is to say, in an intelligence
test.
Errors of Perception
The grocer needs to be assured of the accuracy of his scales, and the
chemist of the high accuracy of his chemical balance; the surveyor
needs to know about the errors that may creep into the process of
measuring the length of a line or angle. All of them, using
instruments to assist in accurate perception of facts, are concerned
about the accuracy of their instruments. Now, we all use the senses in
perceiving facts, and "errors of sense" therefore concern us {447}
all. Some of the errors committed in sense perception can be laid at
the door of the senses, and some rather belong in the sphere of
perception proper.
If you come out of a cold room into a warm room, the latter seems
warmer than it is; and if you come out of a dark room into a light
room, the latter seems brighter than it is. These errors, due to
adaptation of the temperature sense and of the retina, are properly
classed as errors of sense.
If you are taking a child's temperature with a "minute thermometer",
it is best to use your watch to tell you when the minute is up, for
the minute, when you are simply waiting for it to pass, seems very
long. But if you are "working against time", a minute seems short. The
professor is shocked when the closing bell rings, and thinks that
certainly the hour cannot be up; but some of the students have been
consulting their watches for quite a long while, being sure the hour
must be nearly over. These are scarcely errors of sense, but they are
errors of perception.
Where we tend to err in one certain direction from the truth, as in
the examples just cited, psychology speaks of a "constant error", and
evidently the knowledge of such constant errors is of importance
wherever the facts are of importance. In a court of law, a witness
often has to testify regarding the length of time occupied by some
event, and a knowledge of the constant errors in time perception would
therefore be of considerable legal importance. They would need to be
worked out in considerable detail, since they differ according to the
desires and attitude of the witness at the time of the event.
Besides constant errors, there are accidental or variable errors, due
to slight momentary causes. Both constant and variable errors can be
illustrated by a series of shots at a target. The variable error is
illustrated by the scatter of {448} the hits, and the constant error
by the excess of hits above the bull's-eye, or below, or to the right
or left. The constant error can be corrected, once you know what it
is; if results show that you tend to shoot too high, you can
deliberately aim lower. But the variability of any performance cannot
be eliminated except by long practice, and not altogether even then.
[Illustration: Fig. 66.--Constant error and scatter in hitting at a
target. The little circle was the target, but the center of the actual
distribution of the attempts lies at the cross, which was drawn in
afterwards. The constant error could be stated by saying that the
center of distribution was so far from the target, and in such and
such a direction. The scattering of the attempts can be measured
also.]
Experimental psychology has taken great pains in measuring the
accuracy of different sorts of perception. How small a difference in
length can be perceived by the eye, how small a difference of weight
by the hand--these are sample problems in this line.
For example, to measure the fineness with which weights can be
perceived when "hefted" in the hand, you take two objects that are
alike in size and appearance but differing slightly in weight, and
endeavor to decide which is the heavier just by lifting them. You try
repeatedly and keep track of the number of errors, using this number
as a measure of the accuracy of perception. Now, if one weight were
twice as heavy as the other (one, for example, weighing 100 grams
{449} and the other 200), you would never make an error except through
carelessness; but if one were 100 and the other 120 grams, you would
make an occasional error, and the number of errors would increase as
the difference was decreased; finally, comparing 100 and 101 grams,
you would get almost as many wrong as right, so that your perception
of that small difference would be extremely unreliable.
ERRORS IN PERCEIVING SMALL DIFFERENCES
OF WEIGHT (From Warner Brown)
Difference 20 16 12 8 4 8 2 1 grams
Errors 1 2 5 18 28 81 89 44 per hundred trials
The weights were in the neighborhood of 100 grams; each weight was
compared with the 100-gram weight, and each such pair was lifted and
judged 1400 times. Notice that the per cent of errors gradually
increases as the difference becomes smaller.
The smaller the difference between two stimuli, the more numerous the
errors in perceiving it, or, the less perceptible it is, and there is
no sharp line between a difference that can be perceived and one that
is too small to be perceived. That is the first great result from the
study of the perception of small differences.
The second great result is called _Weber's law_, which can be stated
as follows: In the same sort of perception, equal relative (not
absolute) differences are equally perceptible. For example, from the
preceding table we see that 28 per cent. of errors are made in
comparing weights of 100 and 104 grams; then, according to Weber's
law, 28 per cent, of errors would also be made in comparing 200 grams
with 208, or 500 with 520, or 1000 with 1040 grams, or any pair of
weights that stood to each other in the ratio of 100 to 104. Weber's
law is only approximately true for the perception of weights, since
actually fewer errors are committed in comparing 500 and 520 than in
comparing 100 and 104 grams; but the discrepancy is not extremely
great here, and in {450} some other kinds of perception, as especially
in comparing the brightness of lights or the length of seen lines, the
law holds good over a wide range of stimuli and only breaks down near
the upper and lower extremes. We are familiar, in ordinary life, with
the general truth of Weber's law, since we know that an inch would
make a much more perceptible addition to the length of a man's nose
than to his height, and we know that turning on a second light when
only one is already lit gives a much more noticeable increase in the
light than if we add one more light when twenty are already burning.
A third great result of this line of study is that different sorts of
perception are very unequal in their fineness and reliability.
Perception of brightness is about the keenest, as under favorable
conditions a difference of one part in one hundred can here be
perceived with very few errors. Visual perception of length of line is
good for about one part in fifty, perception of lifted weight for
about one part in ten, perception of loudness of sound for about one
part in three. But the perception of small differences in the pitch of
musical tones is keener still, only that, not following Weber's law in
the least, it cannot be expressed in the same way. A person with a
good ear for pitch can distinguish with very few errors between two
tones that differ by only one vibration per second, and can perceive
this same absolute difference equally well, whether the total
vibration rate is 200, 400, or 800 vibrations per second.
Illusions
An error of perception is often called an "illusion", though this term
is commonly reserved for errors that are large and curious. When one
who is being awakened by a bell perceives it as a tom-tom, that is an
illusion. An {451} illusion consists in responding to a sensory
stimulus by perceiving something that is not really there. The
stimulus is there, but not the fact which it is taken to indicate.
Illusion is false perception.
The study of illusions is of value, not only as showing how far a
given kind of perception can be trusted, but also as throwing light on
the process of perception. When a process goes wrong, it sometimes
reveals its inner mechanism more clearly than when everything is
running smoothly. Errors of any kind are meat to the psychologist.
Illusions may be classified under several headings according to the
factors that are operative in causing the deception.
1. Illusions due to peculiarities of the sense organs.
Here the stimulus is distorted by the sense organ and so may easily be
taken as the sign of an unreal fact.
Separate the points of a pair of compasses by about three-quarters of
an inch, and draw them across the mouth, one point above it and the
other below; you will get the illusion of the points separating as
they approach the middle of the mouth (where the sensory nerve supply
is greatest), and coming together again as they are drawn to the cheek
at the other side.
Under this same general head belong also after-images and contrast
colors, and also double vision whenever for any reason the two eyes
are not accurately converged upon an object. The fact that a vertical
line appears longer than an equal horizontal is supposed to depend
upon some peculiarity of the retina. Aside from the use of this class
of illusions in the detailed study of the different senses, the chief
thing to learn from them is they so seldom are full-fledged illusions,
because they are ignored or allowed for, and not taken as the signs of
facts. An after-image would constitute a genuine illusion if it were
taken for some real {452} thing out there; but as a matter of fact,
though after-images occur very frequently--slight ones practically
every time the eyes are turned--they are ignored to such an extent
that the student of psychology, when he reads about them, often thinks
them to be something unusual and lying outside of his own experience.
The same is true of double images. This all goes to show how strong is
the tendency to disregard mere sensation in the interest of getting
objective facts.
2. Illusions due to preoccupation or mental set.
When an insane person hears the creaking of a rocking-chair as the
voice of some one calling him bad names, it is because he is
preoccupied with suspicion. We might almost call this an
hallucination,[Footnote: See p. 375.] since he is projecting his own
auditory images and taking them for real sensations; it is, at any
rate, an extreme instance of illusion. In a milder form, similar
illusions are often momentarily present in a perfectly normal person,
as when he is searching for a lost object and thinks he sees it
whenever anything remotely similar to the desired object meets his
eyes; or as when the mother, with the baby upstairs very much on her
mind, imagines she hears him crying when the cat yowls or the
next-door neighbors start their phonograph. The ghost-seeing and
burglar-hearing illusions belong here as well. The mental set
facilitates responses that are congruous with itself.
3. Illusions of the response-by-analogy type.
This is probably the commonest source of everyday illusions, and the
same principle, as we have seen, is operative in a host of correct
perceptions. Perceiving the obliquely presented rectangle as a
rectangle is an example of correct perception of this type. Perceiving
the buzzing of a fly as an aeroplane is the same sort of response only
that it happens to be incorrect. If the present stimulus has something
in {453} common with the stimulus which has in the past aroused a
certain perception, we may make the same response now as we did
before--especially, of course, if the present mantel set favors this
response.
[Illustration: Fig. 67.--The Ladd-Franklin illusion of monocular
perspective. Close one eye, and hold the book so that the other eye is
at the common center from which the lines radiate; this center is
about 5 inches from the figure. Hold the book horizontally, and just a
little below the eye.]
A good instance of this type is the "proofreader's illusion", so
called, perhaps, because the professional proofreader is less subjcet
to it than any one else. The one most subject to it is the author of a
book, for whom it is almost impossible to find every misspelled word
and other typographical error in reading the proof. Almost every book
comes out with a few such errors, in spite of having been scanned
repeatedly by several people. A couple of misprints have purposely
been left in the last few lines for the reader's benefit. If the word
as printed has enough resemblance to the right word, it arouses the
same percept and enables the reader to get the sense and pass on
satisfied. {454} Before we began to pore over books and pictures, the
lines that we saw usually were the outlines of solid objects, and now
it requires only a bare diagram of lines to arouse in us the
perception of a solid object seen in perspective. An outline drawing,
like those of the cube and staircase used to illustrate ambiguous
perspective, is more readily seen as a solid object than as a flat
figure.
[Illustration: Fig. 68.--Aristotle's illusion.]
Another illusion of this general type dates away back to Aristotle.
Cross two fingers, perhaps best the second and third, and touch a
marble with the crossed part of both fingers, and it seems to be two
marbles; or, you can use the side of your pencil as the stimulus. In
the customary position of the fingers, the stimuli thus received would
mean two objects.
A much more modern illusion of the same general type is afforded by
the moving pictures. The pictures do not actually show an object in
motion; they simply show the object in a series of motionless
positions, caught by instantaneous photography. The projector shows
the series of snap-shots in rapid succession, and conceals them by a
shutter while they are shifted, so as to avoid the blur that would
occur if the picture were itself moved before the eyes. But the series
of snap-shots has so much in common with the visual stimulus got from
an actually present moving object that we make the same perceptive
response. {455} The same illusion in a rudimentary form can be
produced by holding the forefinger upright three or four inches in
front of the nose, and looking at it while winking first the one eye
and then the other. Looked at with the right eye alone it appears to
be more to one side and looked at with the left eye alone it appears
to be more to the other side; and when the one eye is closed and the
other simultaneously opened, the finger seems actually to move from
one position to the other.
[Illustration: Fig. 69.--The pan illusion. The two pan-shaped outlines
are practically identical, but it is hard to compare the corresponding
sides--hard to isolate from the total figure just the elements that
you need to compare.]
4. Illusions due to imperfect isolation of the fact to be perceived.
Here belong, probably, most of the illusions produced in the
psychological laboratory by odd combinations of lines, etc. A figure
is so drawn as to make it difficult to isolate the fact to be
observed, and when the observer attempts to perceive it, he falls into
error. He thinks he is perceiving one fact, when he is perceiving
another. The best example is the Müller-Lyer figure, in which two
equal lines are embellished with extra lines at their ends; you are
supposed to perceive the lengths of the two main lines, but you are
very apt to take the whole figure in the rough and perceive the
distances between its chief parts. You do not succeed in isolating the
precise fact you wish to observe.
{456}
The Müller-Lyer Illusion
The most familiar form of this striking illusion is made with arrow
heads, thus
[Illustration: Inward and outward arrowheads on two equal length lines.]
In attempting to compare the two horizontal lines one is confused so
as to regard the line with outward-extending obliques longer than that
with inward-extending obliques, though, measured from point to point,
they are equal. The same illusion occurs in a variety of similar
figures, such as
[Illustration: Inward and outward arrowheads.]
where the main lines are not drawn, but the distances from point to
point are to be compared; or such as
[Illustration: Inward and outward solid arrowheads.]
where the two distances between points are again to be compared.
Angles, however, are not necessary to give the illusion, as can be
seen in this figure
[Illustration: Half circles with similar spacing.]
or in this
[Illustration: Full circles with similar spacing.]
In the last the lengths to be compared extend (_a_) from the
right-hand rim of circle 1 to the left-hand rim of circle 2, and (_b_)
from this last to the right-hand rim of circle 3. The same illusion
can be got with squares, or even with capital letters as
[Illustration: Upper case E with similar spacing and the center letter
reversed.]
or
[Illustration: Upper case R with similar spacing and the center letter
reversed.]
or
[Illustration: Upper case L E D with similar spacing and the center
letter reversed.]
where the distances between the main vertical lines are to be
compared.
Here is an another form of the same illusion
[Illustration: Two sets of three parallel horizontal lines. In the first
set the center line is longest. In the second set the center line is
shortest, but the same length as the first center line.]
the middle lines being affected by those above and below.
{457}
Though these illusions seem like curiosities, and far from every-day
experience, they really do enter in some degree into almost every
figure that is not perfectly square and simple.
[Illustration: Fig. 70.--The Poggendorf illusion. Are the two obliques
parts of the same straight line?]
Any oblique line, any complication of any sort, is pretty sure to
alter the apparent proportions and directions of the figure. A broad
effect, a long effect, a skewed effect, may easily be produced by
extra lines suitably introduced into a dress, into the front of a
building, or into a design of any sort; so that the designer needs to
have a practical knowledge of this type of illusion.
Extra lines have an influence also upon esthetic perception. The
esthetic effect of a given form may be quite altered by the
introduction of apparently insignificant extra lines.
{458}
[Illustration: Fig. 71.--The barber-pole illusion. The rectangle
represents a round column, around which runs a spiral, starting at
_a_. Which of the lines, 1, 2, 3, 4, and 5, comes closest to being a
continuation of _a?_]
Esthetic perception is very much subject to the law of combination,
and to the resulting difficulty of isolation.
One of the most interesting illusions, not being visual, can {459}
only be described and not demonstrated here.
[Illustration: Fig. 72.--By aid of this simple figure, the
Poggendorf and barber-pole illusions can be seen to be instances of
the Müller-Lyer illusion, Try to bisect the horizontal line in this
figure. The oblique line at the right tends to displace the
right-hand end of the horizontal to the right, while the oblique at
the left tends to displace the left-hand end of the horizontal also
to the right. Similar displacements account for the Poggendorf and
barber-pole illusions.]
[Illustration: Fig. 73.--The Zoellner illusion. The long lines are
really parallel. The illusion is increased by holding the figure so
that these main lines shall be neither vertical nor horizontal. It
is more difficult to "deceive the eye" in regard to the direction of
vertical and horizontal lines, than in regard to the direction of
oblique lines. This illusion must be related in some way to the
Müller-Lyer and Poggendorf illusions, since the elements employed in
constructing the three figures are so much the same.
If you treat this figure according to the directions given for Fig.
67, and sight along the obliques, you get an illusion of
perspective.]
It is called the "size-weight illusion", and may be said to be based
on the old catch, "Which is heavier, a pound of lead or a pound of
feathers?" Of course, we shrewdly answer, a pound's {460} a pound. But
lift them and notice how they feel! The pound of lead feels very much
heavier. To reduce this illusion to a laboratory experiment, you take
two round wooden pill-boxes, one several times as large as the other,
and load them so that they both weigh the same; then ask some one to
lift them and tell which is the heavier. He will have no doubt at all
that the smaller box is the heavier; it may seem two or three times as
heavy. Young children, however, get the opposite illusion,
assimilating the weight to the visual appearance; but older persons
switch over to the contrast effect, and perceive in opposition to the
visual appearance. What seems to happen in the older person is a motor
adjustment for the apparent weights, as indicated by their visual
appearance, with the result that the weight of larger size is lifted
more strongly than the weight of smaller size; so that the big one
comes up easily and seems light, the little one slowly and seems
heavy.
{461}
EXERCISES
1. Outline the chapter.
2. Show that the law of combination accounts both for many
correct perceptions, and for many illusions.
3. Through which of the senses are spatial facts best perceived?
4. "At first, the baby very likely perceives a ball simply as something
for him to handle and throw; but, through the medium of blocked
response, he comes to perceive it more objectively, i.e., as an
object related to other objects, and not simply related to
himself." Explain and illustrate this statement.
5. Give an example from the field of auditory perceptions where
"isolation" is very much in evidence.
6. Can you see any law analogous to Weber's law in the field of
financial profit and loss? Does a dollar gained or lost _seem_ the
same amount, without regard to the total amount possessed?
7. Trial and error perception. Go about the room with closed eyes,
and identify objects by touching them with the hands. Notice
whether your first impression gives place to corrected impressions.
8. Perception of form by "active" and "passive" touch. With
the eyes closed, try to distinguish objects of different shapes (a)
by letting them simply rest upon the skin, and (b) by handling
them. What senses coöperate in furnishing data for "active touch"?
9. Binocular parallax, or the differing views of the same solid object
obtained by the two eyes. Hold a small, three-dimensional object a
foot in front of the face, and notice carefully the view of it
obtained by each eye separately. A pencil, pointing towards the
face, gives very different views. What becomes of the two monocular
views when both eyes are open at once?
10. Binocular compared with monocular perception of "depth"
or distance away. Take a pencil in each hand, and bring the points
together a foot in front of the face, while only one eye is open.
When the points seem to be nearly touching, open the other eye,
and see whether the two points still seem to be close together.
Repeat.
REFERENCES
Discussions of perception that are in some respects fuller than the
present chapter can be found in C. H. Judd's _Psychology, General
Introduction_, 2nd edition, 1917, pp. 162-194; in Titchener's
_Textbook of Psychology_, 1909, pp. 303-373; and in Warren's _Human
Psychology_, 1919, pp. 232-269.
{462}
CHAPTER XVIII
REASONING
THE PROCESS OF MENTAL, AS DISTINGUISHED FROM MOTOR EXPLORATION
We are still on the general topic of "discovery". Indeed, we are still
on the topic of perception; we come now to that form of perception
which is different from sense perception. The reasoner is an explorer,
and the culmination of his explorations is the perception of some fact
previously unknown to him.
Reasoning might be described as mental exploration, and distinguished
from purely motor exploration of the trial and error variety. Suppose
you need the hammer, and go to the place where it is kept, only to
find it gone. Now if you simply proceed to look here and there,
ransacking the house without any plan, that would be motor
exploration. But if, finding this trial and error procedure to be
laborious and almost hopeless, you sit down and think, "Where can that
hammer be? Probably where I used it last!" you may recall using it
for a certain purpose, in a certain place, go there and find it. You
have substituted mental exploration of the situation for purely motor
exploration, and saved time and effort. Such instances show the use of
reasoning, and the part it plays in behavior.
The _process_ of reasoning is also illustrated very well in these
simple cases. It is an exploratory process, a searching for facts. In
a way, it is a trial and error process. If you don't ransack the
house, at least you ransack your memory, in search for facts that will
assist you. You recall this fact {463} and that, you turn this way and
that, mentally, till some fact is recalled that serves your need. No
more in reasoning than in motor exploration can you hope to go
straight to the desired goal.
Animal and Human Exploration
Is man the only reasoning animal? The experimental work on animal
learning, reviewed in one of our earlier chapters, was begun with this
question in mind. Previous evidence on this point had been limited to
anecdotes, such as that of the dog that was found opening a gate by
lifting the latch with his nose, and was supposed to have seen men
open the gate in this way, and to have _reasoned_ that if a man could
do that, why not a dog? The objection to this sort of evidence is that
the dog's manner of acquiring the trick was not observed. Perhaps he
reasoned it out, and perhaps he got it by accident--you cannot tell
without watching the process of learning. You must experiment, by
taking a dog that does not know the trick, and perhaps first "showing
him" how to open the gate by lifting the latch; but it was found that
dogs and cats, and even monkeys, could not learn the trick in this
way. If, however, you placed a dog in a cage, the door of which could
be opened by lifting a latch, and motivated the dog strongly by having
him hungry and placing food just outside, then the dog went to work by
trial and error, and lifted the latch in the course of his varied
reactions; and if he were placed back in the cage time after time, his
unsuccessful reactions were gradually eliminated and the successful
reaction was firmly attached to the situation of being in that cage,
so that he would finally lift the latch without any hesitation.
The behavior of the animal does not look like reasoning. For one
thing, it is too impulsive and motor. The typical {464} attitudes of
the reasoner, whether "lost in thought" or "studying over things", do
not appear in the dog, or even in the monkey, though traces of them
may perhaps be seen in the chimpanzee and other manlike apes. Further,
the animal's learning curve fails to show sudden improvements such as
in human learning curves follow "seeing into" the problem. In short,
there is nothing to indicate that the animal recalls facts previously
observed or sees their bearing on the problem in hand. He works by
motor exploration, instead of mental. He does not search for
"considerations" that may furnish a clue.
The behavior of human beings, placed figuratively in a cage, sometimes
differs very little from that of an animal. Certainly it shows plenty
of trial and error and random motor exploration; and often the puzzle
is so blind that nothing but motor exploration will bring the
solution. What the human behavior does show that is mostly absent from
the animal is (1) attentive studying over the problem, scrutinizing it
on various sides, in the effort to find a clue; (2) thinking,
typically with closed eyes or abstracted gaze, in the effort to recall
something that may bear on the problem; and (3) sudden "insights" when
the present problem is seen in the light of past experience.
Though reason differs from animal trial and error in these respects,
it still is a tentative, try-and-try-again process. The right clue is
not necessarily hit upon at the first try; usually the reasoner finds
one clue after another, and follows each one up by recall, only to get
nowhere, till finally he notices a sign that recalls a pertinent
meaning. His exploration of the situation, though carried on by aid of
recalled experience instead of by locomotion, still resembles finding
the way out of a maze with many blind alleys. In short, reasoning may
be called a trial and error process in the sphere of mental reactions.
{465}
The reader familiar with geometry, which is distinctly a reasoning
science, can readily verify this description. It is true that the
demonstrations are set down in the book in a thoroughly orderly
manner, proceeding straight from the given assumption to the final
conclusion; but such a demonstration is only a dried specimen and does
not by any means picture the living mental process of reasoning out a
proposition. Solving an "original" is far from a straight-forward
process. You begin with a situation (what is "given") involving a
problem (what is to be proved), and, studying over this lay-out you
notice a certain fact which looks like a clue; this recalls some
previous proposition which gives the significance of the clue, but
often turns out to have no bearing on the problem, so that you shift
to another clue; and so on, by what is certainly a trial and error
process, till some fact noted in the situation plus some knowledge
recalled by this fact, taken together, reveal the truth of the
proposition.
Reasoning Culminates in Inference
When you have described reasoning as a process of mental exploration,
you have told only half the story. The successful reasoner not only
seeks, but finds. He not only ransacks his memory for data bearing on
his problem, but he finally "sees" the solution clearly. The whole
exploratory process culminates in a perceptive reaction. What he
"sees" is not presented to his senses at the moment, but he "sees that
something _must_ be so". This kind of perception may be called
_inference_.
To bring out distinctly the perceptive reaction in reasoning, let us
cite a few very simple cases. Two freshmen in college, getting
acquainted, ask about each other's fathers and find that both are
alumni of this same college. "What class was your father in?" "In the
class of 1900. And {466} yours?" "Why, he was in 1900, too. Our
fathers were in the same class; they must know each other!" Here two
facts, one contributed by one person and the other by another person,
enable both to perceive a third fact which neither of them knew
before. Inference, typically, is a response to two facts, and the
response consists in perceiving a third fact that is bound up in the
other two.
You do not infer what you can perceive directly by the senses. If Mary
and Kate are standing side by side, you can _see_ which is the taller.
But if they are not side by side, but Mary's height is given as so
much and Kate's as an inch more, then from these two facts you know,
by inference, that Kate is taller than Mary.
"Have we set the table for the right number of people?" "Well, we can
see when the party comes to the table." "Oh! but we can tell now by
counting. How many are there to be seated? One, two, three--fifteen in
all. Now count the places at table--only fourteen. You will have to
make room for one more." This reducing of the problem to numbers and
then seeing how the numbers compare is one very simple and useful kind
of inference.
Indirect comparison may be accomplished by other similar devices. I
can reach around this tree trunk, but not around that, and thus I
perceive that the second tree is thicker than the first, even though
it may not look so. If two things are each found to be equal to a
third thing, then I see they must be equal to each other; if one is
larger than my yardstick and the other smaller, then I see they must
be unequal.
Of the two facts which, taken together, yield an inferred fact, one is
often a general rule or principle, and the inference then consists in
seeing how the general rule applies to a special case. A dealer offers
you a fine-looking diamond ring for five dollars, but you recall the
rule that "all genuine diamonds are expensive", and perceive that this
{467} diamond must be an imitation. This also is an instance of
indirect comparison, the yardstick being the sum of five dollars; this
ring measures five dollars, but any genuine diamond measures more than
five dollars, and therefore a discrepancy is visible between this
diamond and a genuine diamond. You can't see the discrepancy by the
eye, but you see it by way of indirect comparison, just as you
discover the difference between the heights of Mary and Kate by aid of
the yardstick.
If all French writers are clear, then Binet, a French writer, must be
clear. Here "French writers" furnish your yardstick. Perhaps it would
suit this case a little better if, instead of speaking of indirect
comparison by aid of a mental yardstick, we spoke in terms of
"relations". When you have before your mind the relation of A to M,
and also the relation of B to M, you may be able to see, or infer, a
relation between A and B. M is the common point of reference to which
A and B are related. Binet stands in a certain relation to "French
writers", who furnish the point of reference; that is, he is one of
them. Clear writing stands in a certain relation to French writers,
being one of their qualities; from which combination of relations we
perceive clear writing as a quality of Binet.
Just as an illusion is a false sense perception, so a false inference
is called a "fallacy". One great cause of fallacies consists in the
confused way in which facts are sometimes presented, resulting in
failure to see the relationships clearly. If you read that
"Smith is taller than Brown; and
Jones is shorter than Smith; and therefore
Jones is shorter than Brown,"
the mix-up of "taller" and "shorter" makes it difficult to get the
relationships clearly before you, and you are likely {468} to make a
mistake. Or again, if Mary and Jane both resemble Winifred, can you
infer that they resemble each other? You are likely to think so at
first, till you notice that resemblance is not a precise enough
relation to serve for purposes of indirect comparison. Mary may
resemble Winifred in one respect, and Jane may resemble her in another
respect, and there may be no resemblance between Mary and Jane.
Or, again,
"All French writers are clear; but
James was not a French writer; and therefore
James was not a clear writer,"
may cause some confusion from failure to notice that the relation
between French writers and clear writing is not reversible so that we
could turn about and assert that all clear writers were French.
The reasoner needs a clear head and a steady mental eye; he needs to
look squarely and steadily at his two given statements in order to
perceive their exact relationship. Diagrams and symbols often assist
in keeping the essential facts clear of extraneous matter, and so
facilitate the right response.
To sum up: the process of reasoning culminates in two facts being
present as stimuli, and the response, called "inference", consists in
perceiving a third fact that is implicated in the two stimulus-facts.
It is a good case of the law of combination, and at the same time it
is a case where "isolation" is needed, otherwise the response will be
partly aroused by irrelevant stimuli, and thus be liable to error.
Varieties of Reasoning
Reasoning as a whole is a process of mental exploration culminating in
inference. Now, without regard to possible {469} variations of the
perceptive response of inference, there are at least different
varieties of the exploratory process leading up to inference. The
situation that arouses reasoning differs from one case to another, the
motive for engaging in this rather laborious mental process differs,
and the order of events in the process differs. There are several main
types of reasoning, considered as a process of mental exploration.
1. Reasoning out the solution of a practical problem.
A "problem" is a situation for which we have no ready and successful
response. We cannot successfully respond by instinct or by previously
acquired habit. We must _find out_ what to do. We explore the
situation, partly by the senses and actual movement, partly by the use
of our wits. We observe facts in the situation that recall previous
experiences or previously learned rules and principles, and apply
these to the present case. Many of these clues we reject at once as of
no use; others we may try out and find useless; some we may think
through and thus find useless; but finally, if our exploration is
successful, we observe a real clue, recall a pertinent guiding
principle, and see the way out of our problem.
Two boys went into the woods for a day's outing. They climbed about
all the morning, and ate their lunch in a little clearing by the side
of a brook. Then they started for home, striking straight through the
woods, as they thought, in the direction of home. After quite a long
tramp, when they thought they should be about out of the woods, they
saw clear space ahead, and, pushing forward eagerly, found themselves
in the same little clearing where they had eaten their lunch!
Reasoning process No. 1 now occurred: one of the boys _recalled_ that
when traversing the woods without any compass or landmark, the
traveller is very likely to go in a circle; inference, "That is what
we have done and {470} we probably shall do the same thing again if we
go ahead. We may as well sit down and think it over."
Mental exploration ensued. "How about following the brook?" "That
won't do, for it flows down into a big swamp that we couldn't get
through". "How about telling directions by the sun?" "But it has so
clouded over that you can't tell east from west, or north from south."
"Yes, those old clouds! How fast they are going! They seem to go
straight enough." "Well, say! How about following the clouds? If we
keep on going straight, in any direction, for a couple of hours, we
shall surely get out of the woods somewhere." This seems worth trying
and actually brings the boys out to a road where they can inquire the
way home.
What we find in this case is typical of problem solution. First, a
desire is aroused, and it facilitates the observation and recall of
facts relevant to itself. One pertinent fact is observed, another
pertinent fact, or rule, is recalled; and in these two taken together
the key to the problem is found.
2. Rationalization or self-justification.
While in the preceding case reasoning showed what to do, here it is
called upon to justify what has been done, or what is going to be done
anyway. The question is, what reason to assign for the act; we feel
the need of meeting criticism, either from other people or from
ourselves. The real motive for the act may be unknown to ourselves, as
it often is unless we have made a careful study of motives; or, if
known, it may not be such as we care to confess. We require a
_reasonable_ motive, some acceptable general principle that explains
our action.
A child is unaccountably polite and helpful to his mother some day,
and when asked about it replies that he simply wants to help--while
his real motive may have been to score against his brother or sister,
who is to some extent his rival.
{471}
If I have work requiring attention but want to go to the game, I
should certainly be lacking in reasoning ability if I could not find
something in the situation that made my attendance at the game
imperative. I am stale, and the game will freshen me up and make me
work better afterward. Or, I am in serious danger of degenerating into
a mere "grind", and must fight against this evil tendency. Or, my
presence at the game is necessary in order to encourage the team.
Thus, aspects of the situation that are in line with our desire bob to
the surface and suggest acceptable general principles that make the
intended action seem good and even necessary. Finding excuses for acts
already performed is a reasoning exercise of the same sort. Man is a
rationalizing animal as well as a rational animal, and his
self-justifications and excuses, ludicrous though they often are, are
still a tribute to his very laudable appreciation of rationality.
3. Explanation.
This form of reasoning, like the preceding, takes its start with
something that raises the question, "Why?" Only, our interest in the
question is objective rather than subjective. It is not our own
actions that call for explanation, but some fact of nature or of human
behavior. Why--with apologies to the Southern Hemisphere!--is it so
cold in January? The fact arouses our curiosity. We search the
situation for clues, and recall past information, just as in the
attempt to solve a practical problem. "Is it because there is so much
snow in January?" "But what, then, makes it snow? This clue leads us
in a circle." "Perhaps, then, it is because the sun shines so little
of the time, and never gets high in the sky, even at noon." That is a
pretty good clue; it recalls the general principle that, without a
continued supply of heat, cold is inevitable. To explain a phenomenon
is to deduce it from {472} an accepted general principle; to
understand it is to see it as an instance of the general principle.
Such understanding is very satisfactory, since it rids you of
uncertainty and sometimes from fear, and gives you a sense of power
and mastery.
4. Application.
The reasoning processes discussed up to this point have taken their
start with the particular, and have been concerned in a search for the
general principle that holds good of the given particular case.
Reasoning may also take its start at the other end, in a general
statement, and seek for particular cases belonging under this general
rule. But what can be the motive for this sort of reasoning? What is
there about a general proposition to stimulate exploration?
Several motives may be in play. First, there may be a need for
application of the general principle. Somebody whose authority you
fully accept enunciates a general proposition, and you wish to apply
it to special cases, either for seeing what practical use you can make
of it, or simply to make its meaning more real and concrete to
yourself. Your exploration here takes a different form from that thus
far described. Instead of searching a concrete situation for clues,
and your memory for general principles, you search your memory for
particular cases where the general law should apply. If all animals
are cold-blooded, excepting only birds and mammals, then fish and
frogs and lizards are cold-blooded, spiders, insects, lobsters and
worms; having drawn these inferences, your understanding of the
general proposition becomes more complete.
5. Doubt.
A general proposition may stimulate reasoning because you doubt it,
and wish to find cases where it breaks down. Perhaps somebody makes
the general statement whose authority you do not accept; perhaps he
says it in an assertive way that makes you want to take him down {473}
a peg. Perhaps you are in the heat of an argument with him, so that
every assertion he may make is a challenge. You search your memory for
instances belonging under the doubted general statement, in the hope
of finding one where the general statement leads to a result that is
contrary to fact. "You say that all politicians are grafters. Theodore
Roosevelt was a politician, therefore, according to you, he must have
been a grafter. But he was not a grafter, and you will have to take
back that sweeping assertion."
6. Verification.
This same general type of reasoning, which takes its start with a
general proposition, and explores particular instances in order to see
whether the proposition, when applied to them, gives a result in
accordance with the facts, has much more serious uses; for this is the
method by which a _hypothesis_ is tested in science. A hypothesis is a
general proposition put forward as a guess, subject to verification.
If it is thoroughly verified, it will be accepted as a true statement,
a "law of nature", but at the outset it is only a guess that may turn
out to be either true or false. How shall its truth or falsity be
demonstrated? By deducing its consequences, and testing these out in
the realm of observed fact.
An example from the history of science is afforded by Harvey's
discovery of the circulation of the blood, which was at first only a
hypothesis, and a much-doubted one at that. If the blood is driven by
the heart through the arteries, and returns to the heart by way of the
veins, then the flow of blood in any particular artery must be away
from the heart, and in any particular vein towards the heart. This
deduction was readily verified. Further, there should be little tubes
leading from the smallest arteries over into the smallest veins, and
this discovery also was later verified, when the invention of the
microscope made observation of the capillaries possible. Other
deductions also were verified, {474} and in short all deductions from
the hypothesis were verified, and the circulation of the blood became
an accepted law.
Most hypotheses are not so fortunate as this one; most of them die by
the wayside, since it is much easier to make a guess that shall fit
the few facts we already know than to make one that will apply
perfectly to many other facts at present unknown. A hypothesis is a
great stimulus to the discovery of fresh facts. Science does not like
to have unverified hypotheses lying around loose, where they may trip
up the unwary. It is incumbent on any one who puts forward a
hypothesis to apply it to as many special cases as possible, in order
to see whether it works or not; and if the propounder of the
hypothesis is so much in love with it that he fails to give it a
thorough test, his scientific colleagues are sure to come to the
rescue, for they, on the whole, would be rather pleased to see the
other fellow's hypothesis come to grief. In this way, the rivalry
motive plays a useful part in the progress and stabilizing of science.
Deductive and Inductive Reasoning