HOW WE EXPERIMENT ON THE MIND--EXPERIMENTAL PSYCHOLOGY.
In recent years the growth of the method of experimenting with bodies
in laboratories in the different sciences has served to raise the
question whether the mind may not be experimented with also. This
question has been solved in so far that psychologists produce
artificial changes in the stimulations to the senses and in the
arrangements of the objects and conditions existing about a person,
and so secure changes also in his mental states. What we have seen of
Physiological Psychology illustrates this general way of proceeding,
for in such studies, changes in the physiological processes, as in
breathing, etc., are considered as causing changes in the mind. In
Experimental Psychology, however, as distinguished from Physiological
Psychology, we agree to take only those influences which are outside
the body, such as light, sound, temperature, etc., keeping the subject
as normal as possible in all respects.
A great many laboratories have now been established in connection with
the universities in Germany, France, and the United States. They
differ very much from one another, but their common purpose is so to
experiment upon the mind, through changes in the stimulations to which
the individual is subjected, that tests may be made of his sensations,
his ability to remember, the exactness and kind of movements, etc.
The working of these laboratories and the sort of research carried out
in them may be illustrated best, perhaps, by a description of some of
the results, apparatus, methods, etc., employed in my own laboratory
during the past year. The end in view will, I trust, be considered
sufficient justification for the degree of personal reference which
this occasions; since greater concreteness and reality attach to
definite descriptions such as this. The other laboratories, as those
at Harvard and Columbia Universities, take up similar problems by
similar methods. I shall therefore go on to describe some recent work
in the Princeton laboratory.
Of the problems taken up in the laboratory, certain ones may be
selected for somewhat detailed explanation, since they are from widely
different spheres and illustrate different methods of procedure.
I. _Experiments on the Temperature Sense._--For a score of years it
has been suspected that we have a distinct sense, with a nerve
apparatus of its own, for the feeling of different temperatures on the
skin. Certain investigators found that this was probably true; it is
proved by the fact that certain drugs alter the sensibility of the
skin to hot and cold stimulations.
Another advance was made when it was found that sensations of either
hot or cold may be had from regions which are insensible at the same
time to the other sort of stimulation, cold or hot. Certain minute
points were discovered which report cold when touched with a cold
point, but give no feeling from a hot object; while other points would
respond only with a sensation from heat, never giving cold. It was
concluded that we have two temperature senses, one for hot and the
other for cold.
Taking the problem at this point, Mr. C.[3] wished to define more
closely the relation of the two sorts of sensation to each other, and
thought he could do so by a method by which he might repeat the
stimulation of a series of exact spots, very minute points on the
skin, over and over again, thus securing a number of records of the
results for both hot and cold over a given area. He chose an area of
skin on the forearm, shaved it carefully, and proceeded to explore it
with the smallest points of metals which could be drawn along the skin
without pricking or tearing. These points were attached to metallic
cylinders, and around the cylinders rubber bands were placed; the
cylinders were then thrust in hot or cold water kept at certain
regular temperatures, and lifted by the rubber bands. They were placed
point down, with equal pressure, upon the points of the skin in the
area chosen. In this way, points which responded only to hot, and also
those responding only to cold, were found, marked with delicate ink
marks in each case, until the whole area was explored and marked in
different colours. This had often been done before. It remained to
devise a way of keeping these records, so that the markings might all
be removed from the skin, and new explorations made over the same
surface. This was necessary in order to see whether the results
secured were always the same. The theory that there were certain
nervous endings in the skin corresponding to the little points
required that each spot should be in exactly the same place whenever
the experiment was repeated.
[Footnote 3: Mr. J. F. Crawford, graduate student.]
Mr. C. made a number of so-called "transparent transfer frames." They
are rectangular pieces of cardboard, with windows cut in them. The
windows are covered with thin architect's paper, which is very
transparent. This frame is put over the forearm in such a way that the
paper in the window comes over the markings made on the arm. The
markings show through very clearly, and the points are copied on the
paper. Then certain boundary marks at the corners are made, both on
the paper and on the arm, at exactly the same places, the frame is
removed, and all the markings on the arm are erased except the
boundary points. The result is that at any time the frames can be put
over the arm again by matching the boundary points, and then the
original temperature spots on the skin will be shown by the markings
on the paper window.
Proceeding to repeat the exploration of the same area in this way, Mr.
C makes records of many groupings of points for both hot and cold
sensations on the same area; he then puts the frames one upon another,
holds them up before a window so that they have a bright background,
and is thus able to see at a glance how nearly the results of the
different sittings correspond.
His results, put very briefly, fail to confirm the theory that the
sense of temperature has an apparatus of fixed spots for heat and
other fixed spots for cold. For when he puts the different markings
for heat together he finds that the spots are not the same, but that
those of one frame fall between those of another, and if several are
put together the points fill up a greater or smaller area. The same
for the cold spots; they fill a continuous area. He finds, however, as
other investigators have found, that the heat areas are generally in
large measure separate from the cold areas, only to a certain extent
overlapping here and there, and also that there are regions of the
skin where we have very little sense of either sort of temperature.
The general results will show, therefore, if they should be confirmed
by other investigators, that our temperature sense is located in what
might be called somewhat large blotches on the skin, and not in minute
spots; while the evidence still remains good, however, to show that we
have two senses for temperature, one for cold and the other for hot.
II. _Reaction-Time Experiments._--Work in so-called "reaction times"
constitutes one of the most important and well-developed chapters in
experimental psychology. In brief, the experiment involved is this:
To find how long it takes a person to receive a sense impression of
any kind--for example, to hear a sound-signal--and to move his hand or
other member in response to the impression. A simple arrangement is as
follows: Sit the subject comfortably, tap a bell in such a way that
the tapping also makes an electric current and starts a clock, and
instruct the subject to press a button with his finger as soon as
possible after he hears the bell. The pressing of the button by him
breaks the current and stops the clock. The dial of the clock
indicates the actual time which has elapsed between the bell (signal)
and his response with his finger (reaction). The clock used for exact
work is likely to be the Hipp chronoscope, which gives on its dials
indications of time intervals in thousandths of a second. For the sake
of keeping the conditions constant and preventing disturbance, the
wires are made long, so that the clock and the experimenter may be in
one room, while the bell, the punch key, and the subject are in
another, with the door closed. This method of getting reaction times
has been in use for a number of years, especially by the astronomers
who need to know, in making their observations, how much time is taken
by the observer in recording a transit or other observation. It is
part of the astronomer's "personal equation."
Proceeding with this "simple-reaction" experiment as a basis, the
psychologists have varied the instructions to the subject so as to
secure from him the different times which he takes for more
complicated mental processes, such as distinguishing between two or
more impressions, counting, multiplying, dividing, etc., before
reacting; or they have him wait for an associated idea to come up
before giving his response, with many other variations. By comparing
these different times among themselves, interesting results are
reached concerning the mental processes involved and also about the
differences of different individuals in the simpler operations of
their daily lives. The following research carried out by Mr. B.[4]
serves to illustrate both of these assertions.
[Footnote 4: The writer.]
Mr. B. wished to inquire further into a fact found out by several
persons by this method: the fact that there is an important difference
in the length of a person's reaction time according to the direction
of his attention during the experiment. If, for example, Mr. X. be
tested, it is possible that he may prefer to attend strictly to the
signal, letting his finger push the key without direct care and
supervision. If this be true, and we then interfere with his way of
proceeding, by telling him that he must attend to his finger, and
allow the signal to take care of itself, we find that he has great
difficulty in doing so, grows embarrassed, and his reaction time
becomes very irregular and much longer. Yet another person, say Y, may
show just the opposite state of things; he finds it easier to pay
attention to his hand, and when he does so he gets shorter and also
more regular times than when he attends to the signal-sound.
It occurred to Mr. B. that the striking differences given by different
persons in this matter of the most favourable direction of the
attention might be connected with the facts brought out by the
physiological psychologists in connection with speech; namely, that
one person is a "visual," in speaking, using mainly sight images of
words, while another is a "motor," using mainly muscular images, and
yet another an "auditive," using mainly sound images. If the
differences are so marked in the matter of speech, it seemed likely
that they might also extend to other functions, and the so-called
"type" of a person in his speech might show itself in the relative
lengths of his reaction times according as he attended to one class of
images or another.
Calling this the "type theory" of reaction times, and setting about
testing four different persons in the laboratory, the problem was
divided into two parts; first, to direct all the individuals selected
to find out, by examining their mental preferences in speaking,
reading, writing, dreaming, etc., the class of images which they
ordinarily depended most upon; and then to see by a series of
experiments whether their reaction times to these particular classes
of images were shorter than to others, and especially whether the
times were shorter when attention was given to these images than when
it was given to the muscles used in the reactions. The meaning of this
would be that if the reaction should be shorter to these images than
to the corresponding muscle images, or to the other classes of images,
then the reaction time of an individual would show his mental type and
be of use in testing it. This would be a very important matter if it
should hold, seeing that many questions both in medicine and in
education, which involve the ascertaining of the mental character of
the individual person, would profit by such an exact method.
The results on all the subjects confirmed the supposition. For
example, one of them, Mr. C., found from an independent examination of
himself, most carefully made, that he depended very largely upon his
hearing in all the functions mentioned. When he thought of words, he
remembered how they sounded; when he dreamed, his dreams were full of
conversation and other sounds. When he wrote, he thought continually
of the way the words and sentences would sound if spoken. Without
knowing of this, many series of reaction experiments were made on him;
the result showed a remarkable difference between the lengths of his
reactions, according as he directed his attention to the sound or to
his hand; a difference showing his time to be one half shorter when he
paid attention to the sound. The same was seen when he reacted to
lights; the attention went preferably to the light, not to the hand;
but the difference was less than in the case of sounds. So it was an
unmistakable fact in his case that the results of the reaction
experiments agreed with his independent decision as to his mental
type.
In none of the cases did this correspondence fail, although all were
not so pronounced in their type preferences as was Mr. C.
The second part of the research had in view the question whether
reaction times taken upon speech would show the same thing; that is,
whether in Mr. C.'s case, for example, it would be found that his
reaction made by speaking, as soon as he heard the signal or saw the
light, would be shorter when he paid attention to the signal than when
he gave attention to his mouth and lips. For this purpose a mouth key
was used which made it possible for the subject simply by emitting a
puff of breath from the lips, to break an electric current and thus
stop the chronoscope as soon as possible after hearing the signal.
The mouth key is figured herewith (Fig. 6).
[Illustration: FIG. 6.--Mouth-key (Isometric drawing) The metallic
tongue E swings over the mercury H, making or breaking the circuit A H
E D B or C E H A. The tongue is moved by a puff of air through the
funnel F. (Devised by Prof. W. Libbey.)]
This experiment was also carried out on all the subjects, none of them
having any knowledge of the end in view, and the experimenters also
not having, as yet, worked out the results of the earlier research. In
all the cases, again, the results showed that, for speech, the same
thing held as for the hand--namely, that the shortest reaction times
were secured when the subject paid attention to the class of images
for which he had a general preference. In Mr. C.'s case, for example,
it was found that the time it took him to speak was much shorter when
he paid strict attention to the expected sound than when he attended
to his vocal organs. So for the other cases. If the individual's
general preference is for muscular images, we find that the quickest
time is made when attention is given to the mouth and lips. Such is
the case with Mr. B.
The general results go to show, therefore--and four cases showing no
exception, added to the indications found by other writers, make a
general conclusion very probable--that in the differences in reaction
times, as secured by giving the attention this way or that, we have
general indications of the individual's temperament, or at least of
his mental preferences as set by his education. These indications
agree with those found in the cases of aphasia known as "motor,"
"visual," "auditory," etc., already mentioned. The early examination
of children by this method would probably be of great service in
determining proper courses of treatment, subjects of study, modes of
discipline, tendencies to fatigue and embarrassment, and the direction
of best progress in education.
This research may be taken to illustrate the use of the reaction-time
method in investigating such complex processes as attention,
temperament, etc. The department which includes the various time
measurements in psychology is now called Mental Chronometry, the older
term, Psychometry, being less used on account of its ambiguity.
III. _An Optical Illusion._--In the sphere of vision many very
interesting facts are constantly coming to light. Sight is the most
complex of the senses, the most easily deranged, and, withal, the most
necessary to our normal existence. The report of the following
experimental study will have the greater utility, since, apart from
any intrinsic novelty or importance the results may prove to have, it
shows some of the general bearings of the facts of vision in relation
to Æsthetics, to the theory of Illusions, and to the function of
Judgment.
Illusion of the senses is due either to purely physiological causes or
to the operation of the principle of Assimilation, which has already
been remarked upon. In the latter case it illustrates the fact that at
any time there is a general disposition of the mind to look upon a
thing under certain forms, patterns, etc., to which it has grown
accustomed; and to do this it is led sometimes to distort what it sees
or hears unconsciously to itself. So it falls into errors of judgment
through the trap which is set by its own manner of working. Nowhere is
the matter better illustrated than in the sphere of vision. The number
of illusions of vision is remarkable. We are constantly taking shapes
and forms for something slightly different from what, by measurement,
we actually find them to be. And psychologists are attempting--with
rather poor success so far--to find some general principles of the
mechanism of vision which will account for the great variety of its
illusions.
Among these principles one is known as Contrast. It is hardly a
principle as yet. It is rather a word used to cover all illusions
which spring up when surfaces of different sizes and shapes, looked at
together or successively, are misjudged with reference to one another.
Wishing to investigate this in a simple way, the following experiment
was planned and carried out by Mr. B.
He wished to find out whether, if two detached surfaces of different
sizes be gazed at together, the linear distances of the field of
vision (the whole scene visible at once) would be at all misjudged. To
test this, he put in the window (W)[5] of the dark room a filling of
white cardboard in which two square holes had been cut (S S'). The
sides of the squares were of certain very unequal lengths. Then a slit
was made between the middle points of the sides of the squares next to
each other, so that there was a narrow path or trough joining the
squares between their adjacent sides. Inside the dark room he arranged
a bright light so that it would illuminate this trough, but not be
seen by a person seated some distance in front of the window in the
next room. A needle (D) was hung on a pivot behind the cardboard, so
that its point could move along the bright trough in either direction;
and on the needle was put the armature (A) of an electro-magnet which,
when a current passed, would be drawn instantly to the magnet (E), and
so stop the needle exactly at the point which it had then reached. A
clock motor (Cm) was arranged in such a way as to carry the needle
back and forth regularly over the slit; and the electro-magnet was
connected by wires with a punch key (K) on a table beside the subject
in the next room. All being now ready, the subject, Mr. S., is told to
watch the needle which appears as a bead of light travelling along the
slit, and stop it when it comes to the middle point of the line, by
pressing the electric key. The experimenter, who stands behind the
window in the dark room, reads on a scale (mm.) marked in millimetres
the exact point at which the needle stops, releases the needle by
breaking the current, thus allowing it to return slowly over the line
again. This gives the subject another opportunity to stop it at what
he judges to be the exact middle of the line, and so on. The
accompanying figure (Fig. 7) shows the entire arrangement.
[Footnote 5: This and the following letters in parentheses refer to
Fig. 7]
[Illustration: FIG. 7]
A great many experiments performed in this way, with the squares set
both vertically and horizontally, and with several persons, brought a
striking and very uniform result. The point selected by the subject as
the middle is regularly too far toward the smaller square. Not a
little, indeed, but a very appreciable amount. The amount of the
displacement, or, roughly speaking, of the illusion, increases as the
larger square is made larger and the smaller one smaller; or, put in a
sentence, the amount varies directly with the ratio of the smaller to
the larger square side.
Finding such an unmistakable illusion by this method, Mr. B. thought
that if it could be tested by an appeal to people generally, it would
be of great gain. It occurred to him that the way to do this would be
to reverse the conditions of the experiment in the following way: He
prepared the figures given in Plate I, in which the two squares are
made of suitable relative size, a line is drawn between them, and a
point on the line is plainly marked. This he had printed in a weekly
journal, and asked the readers of the journal to get their friends,
after merely looking at the figure (i. e., without knowing the result
to be expected), to say--as the reader may now do before reading
further--whether the point on the line (Plate I) is in the middle or
not; and if not, in which direction from the true middle it lies. The
results from hundreds of persons of all manner of occupations, ages,
and of both sexes, agree in saying that the point lies too far toward
the larger square. In reality it is in the exact middle. This is just
the opposite of the result of the experiments in the laboratory, where
the conditions were the reverse, i. e., to find the middle as it
appears to the eye. Here, therefore, we have a complete confirmation
of the illusion; and it is now fully established that in all cases in
which the conditions of this experiment are realized we make a
constant mistake in estimating distances by the eye.[6]
[Footnote 6: In redrawing the figure on a larger sheet (which is
recommended), the connecting line may be omitted, only the mid-point
being marked. Some get a better effect with two circles, the
intervening distance being divided midway by a dot, as in Plate II.]
For instance, if a town committee wish to erect a statue to their
local hero in the public square, and if on two opposite sides of the
square there are buildings of very different heights, the statue
should not be put in the exact middle of the square, if it is to give
the best effect from a distance. It should be placed a little toward
the smaller building. A colleague of the writer found, when this was
first made public, that the pictures in his house had actually been
hung in such a way as to allow for this illusion. Whenever a picture
was to be put up between two others of considerable difference of
size, or between a door (large) and a window (small), it had actually
been hung a little nearer to the smaller--toward the small picture or
toward the window--and not in the true middle.
It is probable that interesting applications of this illusion may be
discovered in æsthetics. For wherever in drawing or painting it is
wished to indicate to the observer that a point is midway between two
lines of different lengths, we should find that the artist, in order
to produce this effect most adequately, deviates a little from the
true middle. So in architecture, the effect of a contrast of masses
often depends upon the sense of bilateral balance, symmetry, or
equality, in which this visual error would naturally come into play.
Indeed, it is only necessary to recall to mind that one of the
principal laws of æsthetic effect in the matter of right line
proportion is the relation of "one to one," as it is called, or equal
division, to see the wide sphere of application of this illusion. In
all such cases the mistake of judgment would have to be allowed for if
masses of unequal size lie at the ends of the line which is to be
divided.
IV. _The Accuracy of Memory._--Another investigation may be cited to
illustrate quite a different department. It aimed to find out
something about the rate at which memory fades with the lapse of time.
Messrs. W., S., and B.[7] began by formulating the different ways in
which tests may be made on individuals to see how accurate their
memories are after different periods of time. They found that three
different tests might be employed, and called them "methods" of
investigating memory. These are, first, the method of Reproduction.
The individual is asked to reproduce, as in an oral or written
examination, what he remembers of something told him a certain time
before. This is the ordinary method of the schools and colleges, of
civil-service examinations, etc. Second, the method of Identification,
which calls upon the person to identify a thing, sentence, report,
etc., a second or third time, as being the same in all respects as
that which he experienced the first time it appeared. Third, the
method of Selection, in which we show to the person a number of
things, sentences, reports, descriptions of objects, etc., and require
him to select from them the ones which are exactly the same as those
he has had before. These methods will be better understood from the
account now to be given of the way they were carried out on a large
number of students.
[Footnote 7: Prof. H. C. Warren, Mr. W. J. Shaw, and the writer.]
The first experiments were made by Messrs. S. and B. in the University
of Toronto on a class of students numbering nearly three hundred, of
whom about one third were women. The instructors showed to the class
certain squares of cardboard of suitable size, and asked them to do
the following three things on different days: First, to reproduce from
memory, with pencil on paper, squares of the same size as those shown,
after intervals of one, ten, twenty, and forty minutes (this gives
results by the method of Reproduction); second, to say whether a new
set of squares, which were shown to them after the same intervals,
were the same in size as those which they had originally seen,
smaller, or larger (illustrating the method of Identification); third,
they were shown a number of squares of slightly different sizes, again
at the same intervals, and asked to select from them the ones which
they found to be the same size as those originally seen (method of
Selection).
The results from all these experiments were combined with those of
another series, secured from a large class of Princeton students; and
the figure (Fig. 8) shows by curves something of the result. The
figure is given in order that the reader may understand by its
explanation the "graphic method" of plotting statistical results,
which, with various complications, is now employed in psychology as
well as in the other positive sciences.
[Illustration: FIG. 8.--Memory curves: I. Method of Selection. II.
Method of Identification.]
Briefly described in words, it was found that the three methods agreed
(the curves are parallel)[8] in showing that during the first ten
minutes there was a great falling off in the accuracy of memory (slant
in the curves from 0 to 10); that then, between ten and twenty
minutes, memory remained relatively faithful (the curves are nearly
level from 10 to 20), and that a rapid falling off in accuracy
occurred after twenty minutes (shown by the slant in the lines from 20
to 40).
[Footnote 8: This figure shows curves for two of the methods only,
Selection and Identification.]
Further, the different positions of the curves show certain things
when properly understood. The curve secured by the method of
Reproduction (not given in the figure) shows results which are least
accurate, because most variable. The reason of this is that in drawing
the squares to reproduce the one remembered, the student is
influenced by the size of the paper he uses, by the varying accuracy
of his control over his hand and arm (the results vary, for example,
according as he uses his right or left hand), and by all sorts of
associations with square objects which may at the time be in his mind.
In short, this method gives his memory of the square a chance to be
fully assimilated to his current mental state during the interval, and
there is no corrective outside of him to keep him true.
That this difficulty is a real one no one who has examined students
will be disposed to deny. When we ask them to reproduce what the
text-book or the professor's lectures have taught, we also ask them to
express themselves accurately. Now the science of correct expression
is a thing in which the average student has had no training. With his
difficulty in remembering is connected his difficulty of expression;
and with it all goes a certain embarrassment, due to responsibility,
personal fear, and dread of disgrace. So the results finally obtained
by this method are really very complex.
One of the curves, that given by the method of Selection (I), also
shows memory to be interfered with by a certain influence. We saw in
connection with the experiments reported above that, even in the most
elementary arrangements of squares in the visual fields, an element of
contrast comes in to interfere with our judgment of size. This we find
confirmed in these experiments when the method of Selection is used.
By this method we show a number of squares side by side, asking the
individual to select the one he saw before. All the squares, being
shown at once, come into contrast with one another on the background;
and so his judgment of the size of the one he remembers is distorted.
This, again, is a real influence in our mental lives, leading to
actual illusion. An unscrupulous lawyer may gradually modify the story
which his client or a witness tells by constantly adding to what is
really remembered, other details so expertly contrasted with the
facts, or so neatly interposed among them, that the witness gradually
incorporates them in his memory and so testifies more nearly as the
lawyer desires. In our daily lives another element of contrast is also
very strong--that due to social opinion. We constantly modify our
memories to agree more closely with the truths of social belief,
paring down unconsciously the difference between our own and others'
reports of things. If several witnesses of an event be allowed to
compare notes from time to time, they will gradually come to tell more
nearly the same story.
The other curve (II) in the figure, that secured by the method of
Identification, seemed to the investigators to be the most accurate.
It is not subject to the errors due to expression and to contrast, and
it has the advantage of allowing the subject the right to recognise
the square. It is shown to him again, with no information that it is
the same, and he decides whether from his remembrance of the earlier
one, it is the same or not. The only objection to this method is that
it requires a great many experiments in order to get an average
result. To be reliable, an average must be secured, seeing that, for
one or two or a few trials, the student may guess right without
remembering the original square at all. By taking a large number of
persons, such as the three hundred students, this objection may be
overcome. Comparing the averages, for example, of the results given
by the men and women respectively, we found practically no difference
between them.
This last point may serve to introduce a distinction which is
important in all work in experimental psychology, and one which is
recognised also in many other sciences--the distinction between
results obtained respectively from one individual and from many. Very
often the only way to learn truth about a single individual is to
investigate a number together. In all large classes of things,
especially living things, there are great individual differences, and
in any particular case this personal variation may be so large that it
obscures the real nature of the normal. For example, three large sons
may be born to two small parents; and from this case alone it might be
inferred that all small parents have large sons. Or three girls might
have better memories than three boys in the same family or school, and
from this it might be argued that girls are better endowed in this
direction than boys. In all such cases the proper thing to do is to
get a large number of cases and combine them; then the preponderance
which the first cases examined may have shown, in one direction or the
other, is corrected. This gives rise to what is called the statistical
method; it is used in many practical matters, such as life insurance,
but its application to the facts of life, mind, variation, evolution,
etc., is only begun. Its neglect in psychology is one of the crying
defects of much recent work. Its use in complicated problems involves
a mathematical training which people generally do not possess; and its
misuse through lack of exactness of observation or ignorance of the
requirements is worse than its neglect.
Another result came out in connection with these experiments on
memory, which, apart from its practical interest, may serve to show an
additional resource of experimental psychology. In making up the
results of a series of experiments it is very important to observe the
way in which the different cases differ from one another. Some cases
may be so nearly alike that the most extreme of them are not far from
the average of them all; as we find, for example, if we measure a
thousand No. 10 shot. But now suppose we mix in with the No. 10 some
No. 6 and some No. 14, and then take the average size; we may now get
just the same average, and we can tell that this pile is different
from the other only by observing the individual measurements of the
single shot and setting down the relative frequency of each particular
size. Or, again, we may get a different average size in one of two
ways: either by taking another lot of uniform No. 14 shot, let us say,
or by mixing with the No. 10 a few very large bullets. Which is
actually the case would be shown only by the examination of the
individual cases. This is usually done by comparing each case with the
average of the whole lot, and taking the average of the differences
thus secured--a quantity called the "mean variation."
In the case of the experiments with the squares, the errors in the
judgments of the students were found to lie always in one direction.
The answers all tended to show that they took, for the one originally
shown, a square which was really too large. Casting about for the
reason of this, it was considered necessary to explain it by the
supposition that the square remembered had in the interval become
enlarged in memory. The image was larger when called up after ten or
twenty minutes than it was before. This might be due to a purely
mental process; or possibly to a sort of spreading-out of the brain
process in the visual centre, giving the result that whenever, by the
revival of the brain process, the mental image is brought back again
to mind, this spreading out shows itself by an enlargement of the
memory image. However it may be explained, the indications of it were
unmistakable--unless, of course, some other reason can be given for
the uniform direction of the errors; and it is further seen in other
experiments carried out by Messrs. W. and B. and by Dr. K.[9] at a
later date.
[Footnote 9: Dr. F. Kennedy, demonstrator, now professor in the
University of Colorado (results not yet published).]
If this tendency to the enlargement of our memories with the lapse of
time should be found to be a general law of memory, it would have
interesting bearings. It would suggest, for instance, an explanation
of the familiar fact that the scenes of the past seem to us, when we
return to them, altogether too small. Our childhood home, the old
flower garden, the height of house and trees, and even that of our
hero uncle, all seem to the returning traveller of adult life
ridiculously small. That we expect them to be larger may result from
the fact that the memory images have undergone change in the direction
of enlargement.
V. _Suggestion._--Space permits only the mention of another research,
which, however, should not be altogether omitted, since it illustrates
yet other problems and the principles of their solution. This is an
investigation by Messrs. T. and H.,[10] which shows the remarkable
influence of mental suggestions upon certain bodily processes which
have always been considered purely physiological. These investigators
set out to repeat certain experiments of others which showed that if
two points, say those of a pair of compasses, be somewhat separated
and put upon the skin, two sensations of contact come from the points.
But if while the experiment is being performed the points be brought
constantly nearer to each other, a time arrives when the two are felt
as only one, although they may be still some distance apart. The
physiologists argued from this that there were minute nerve endings in
the skin at least so far apart as the least distance at which the
points were felt as two; and that when the points were so close
together that they only touched one of these nerve endings, only one
sensation was produced. Mr. T. had already found, working in Germany,
that, with practice, the skin gradually became more and more able to
discriminate the two points--that is, to feel the two at smaller
distances; and, further, that the exercise of the skin in this way on
one side of the body not only made that locality more sensitive to
minute differences, but had the same effect, singularly, on the
corresponding place on the other side of the body. This, our
experimenters inferred, could only be due to the continued suggestion
in the mind of the subject that he should feel two points, the result
being an actual heightening of the sensibility of the skin. When he
thought that he was becoming more sensitive on one side--and really
was--this sense or belief of his took effect in some way in both
hemispheres of his brain, and so both sides of the body were alike
affected.
[Footnote 10: G. A. Tawney, now professor in Beloit College, and C. W.
Hodge, now professor in Lafayette College.]
This led to other experiments in Princeton in which suggestions were
actually made to the subjects that they were to become more or less
sensitive to distance and direction between the points on the skin,
with the striking result that these suggestions actually took effect
all over the body. This was so accurately determined that from the
results of the experiments with the compasses on the skin in this case
or that, pretty accurate inferences could be made as to what mental
suggestions the subject was getting at the time. There was no chance
for deception in the results, for the experiments were so controlled
that the subject did not know until afterward of the correspondences
actually reached between his states of mind and the variations in
sensibility of the skin.
This slight report of the work done in one laboratory in about two
sessions, involving a considerable variety of topics, may give an
idea, so far as it goes, of the sort of work which experimental
psychology is setting itself to do. It will be seen that there is as
yet no well-knit body of results on which new experiments may proceed,
and no developed set of experimental arrangements, such as other
positive sciences show. The procedure is, in many important matters,
still a matter of the individual worker's judgment and ability. Even
for the demonstrations attempted for undergraduate students, good and
cheap apparatus is still lacking. For these reasons it is premature as
yet to expect that this branch of the science will cut much of a
figure in education. There can be no doubt, however, that it is making
many interesting contributions to our knowledge of the mind, and that
when it is more adequately organized and developed in its methods and
apparatus, It will become the basis of discipline of a certain kind
lying between that of physical science and that of the humanities,
since it will have features in common with the biological and natural
sciences. Its results may be expected also to lead to better results
than we now have in the theory and practice of education.