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The Dancing Mouse by Robert M. Yerkes

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3 Oct. 1 3 7 4 6
4 2 5 5 3 7
5 3 3 7 5 5
6 4 6 4 5 5
7 5 5 5 5 5
8 6 -- -- 3 7
9 7 -- -- 6 4
10 8 -- -- 4 6

Averages 4.7 5.3 4.5 5.5

The account of my color vision experiments is finished. If it be objected
that other than visual conditions may account for whatever measure of
discriminating ability, apart from brightness discrimination, appears in
some of the series, the results of the series of Table 29, in which all
conceivable visual means of discrimination were purposely excluded, and
those of the several check tests which have been described from time to
time in the foregoing account, should furnish a satisfactory and definite
answer. I am satisfied that whatever discrimination occurred was due to
vision; whether we are justified in calling it color vision is quite
another question.

I conclude from my experimental study of vision that although the dancer
does not possess a color sense like ours, it probably discriminates the
colors of the red end of the spectrum from those of other regions by
difference in the stimulating value of light of different wave lengths,
that such specific stimulating value is radically different in nature from
the value of different wave lengths for the human eye, and that the red of
the spectrum has a very low stimulating value for the dancer. In the light
of these experiments we may safely conclude that many, if not most, of the
tests of color vision in animals which have been made heretofore by other
investigators have failed to touch the real problem because the
possibility of brightness discrimination was not excluded.

Under the direction of Professor G. H. Parker, Doctor Karl Waugh has
examined the structure of the retina of the dancing mouse for me, with the
result that only a single type of retinal element was discovered.
Apparently the animals possess rod-like cells, but nothing closely similar
to the cones of the typical mammalian retina. This is of peculiar interest
and importance in connection with the results which I have reported in the
foregoing pages, because the rods are supposed to have to do with
brightness or luminosity vision and the cones with color vision. In fact,
it is usually supposed that the absence of cones in the mammalian retina
indicates the lack of color vision. That this inference of functional
facts from structural conditions is correct I am by no means certain, but
at any rate all of the experiments which I have made to determine the
visual ability of the dancer go to show that color vision, if it exists at
all, is extremely poor. It is gratifying indeed to learn, after such a
study of behavior as has just been described, that the structural
conditions, so far as we are able to judge at present, justify the
conclusions which have been drawn.



Darting hither and thither in its cage, whirling rapidly, now to the left,
now to the right, running in circles, passing through holes in the nest
box quickly and neatly, the dancer, it would seem, must have excellent
sight. But careful observation of its behavior modifies this inference.
For it appears that a pair of mice dancing together, or near one another,
sometimes collide, and that it is only those holes with which the animal
is familiar that are entered skillfully. In fact, the longer one observes
the behavior of the dancer under natural conditions, the more he comes to
believe in the importance of touch, and motor tendencies. Sight, which at
first appears to be the chief guiding sense, comes to take a secondary
place. In this chapter it is my purpose to show by means of simple
experiments what part sight plays in the dancer's life of habit formation.

The evidence on this subject has been obtained from four sources: (1)
observation of the behavior of dancers in their cages; (2) observation of
their behavior when blinded; (3) observation of their behavior in a great
variety of discrimination experiments, many of which have already been
described; and (4) observation of their behavior in labyrinth experiments
which were especially planned to exhibit the importance of the several
kinds of vision which the dancer might be supposed to possess. The
evidence from the first three of these sources may be presented summarily,
for much of it has already appeared in earlier chapters. That from the
fourth source will constitute the bulk of the material of this chapter.

My observation of the behavior of the mice has furnished conclusive
evidence of their ability to see moving objects. But that they do not see
very distinctly, and that they do not have accurate perception of the form
of objects, are conclusions which are supported by observations that I
have made under both natural and experimental conditions. In Chapters VII,
VIII, IX, and X, I have presented an abundance of evidence of brightness
vision and, in addition, indications of a specific sensitiveness to wave
length which may be said to correspond to our color vision. It is
noteworthy, however, that all of the experimental proofs of visual ability
were obtained as the result of long periods of training. Seldom, indeed,
in my experience with them, have the dancers under natural conditions
exhibited forms of activity which were unquestionably guided by vision.

It is claimed by those who have experimented with blinded dancers that the
loss of sight decreases the amount and rapidity of movement, and the
ability of the animals to avoid obstacles.

By means of the discrimination method previously used in the preliminary
experiments on color vision, a full description of which may be found in
Chapter IX, p. 133, the dancers' ability to perceive form was tested.
Immediately after the two males _A_ and _B_ had been given the "food-box"
tests, whose results appear in Table 15, they were tested in the same
apparatus and by the same method for their ability to discriminate a
rectangular food-box from a round one. In the case of the color
discrimination tests, it will be remembered that the circular tin boxes 5
cm. in diameter by 1.5 cm. in depth, one of which was covered with blue
paper, the other with orange, were used. For the form discrimination tests
I used instead one of the circular boxes of the dimensions given above and
a rectangular box 8.5 cm. long, 5.5 cm. wide and 2.5 cm. deep. "Force" was
placed in the circular box. The tests were given, in series of 20, daily.



1 Jan. 5 10 10 9 11
2 7 12 8 13 7
3 10 6 14 10 10
4 11 7 13 10 10
5 12 9 11 10 10
6 13 11 9 11 9
7 14 13 7 9 11
8 15 10 10 11 9
9 16 10 10 11 9
10 17 11 9 9 11
11 18 11 9 12 8
12 19 12 8 10 10
13 20 10 10 12 8
14 21 10 10 8 12
15 22 10 10 10 10

Totals 152 148 155 145

The results of 15 series of these tests, as may be seen by the examination
of Table 30, are about as definitely negative, so far as form
discrimination is in question, as they possibly could be. From the first
series to the last there is not one which justifies the inference that
either of the dancers depended upon the form of the boxes in making its
choice. In view of the general criticisms I have made concerning the use
of hunger as a motive in experiments on animal behavior, and in view of
the particular criticisms of this very method of testing the
discriminating powers of the mouse, it may seem strange that space should
be given to a report of these tests. I sympathize with the feeling, if any
one has it, but, at the same time, I wish to call attention to the fact
that almost any mammal which is capable of profiting by experience, and
which, under the same conditions, could distinguish the rectangular box
from the circular one, would have chosen the right box with increasing
accuracy as the result of such experience. The results are important in my
opinion, not because they either prove or disprove the ability of the
dancer to discriminate these particular forms, the discrimination of which
might fairly be expected of any animal with an image-forming eye, but
because they demonstrate an important characteristic of the dancing mouse,
namely, its indifference to the straightforward or direct way of doing

Most mammals which have been experimentally studied have proved their
eagerness and ability to learn the shortest, quickest, and simplest route
to food without the additional spur of punishment for wandering. With the
dancer it is different. It is content to be moving; whether the movement
carries it directly towards the food is of secondary importance. On its
way to the food-box, no matter whether the box be slightly or strikingly
different from its companion box, the dancer may go by way of the wrong
box, may take a few turns, cut some figure-eights, or even spin like a top
for seconds almost within vibrissa-reach of the food-box, and all this
even though it be very hungry. Activity is pre-eminently important in the
dancer's life.

In passing I may emphasize the importance of the fact that at no time did
the brightness or color discrimination tests furnish evidence of attempts
on the part of the dancers to choose by means of slight differences in the
form of the cardboards or the cardboard carriers. Several times form
differences, which were easily perceivable by the human subject, were
introduced in order to discover whether the mice would detect them and
learn to discriminate thereby instead of by the visual conditions of
brightness or color. As these experiments failed to furnish evidences of
form discrimination, the following special test in the discrimination box
was devised.

[Illustration: FIGURE 22.--Cards used for tests of form discrimination.]

The color discrimination box of Chapter X was arranged so that the light
at the entrance to each electric-box had a value of 20 candle meters, less
the diminution caused by a piece of ground glass which was placed over the
end of the electric-boxes to diffuse the light. The windows through which
the light entered the electric-boxes were covered with pieces of black
cardboard; in one of these cardboards I had cut a circular opening 4 cm.
in diameter, and in the other an opening of the same area but markedly
different shape. These openings are shown in Figure 22. As the mouse
approached the entrance to the electric-boxes, it was confronted by these
two equally illuminated areas, whose chief difference was one of form.
Difference in the amount of light within the boxes was excluded so far as
possible. The question which I asked was, can the dancer discriminate by
means of this difference in visual form?

For the purpose of settling this point and of gaining additional knowledge
of the role of vision, two individuals were tested in the discrimination
box under the conditions which have just been described. During the first
ten days of the experiment each of these mice, Nos. 420 and 425, was given
a series of ten tests daily. At the end of this period experimentation
with No. 425 had to be discontinued, and the number of daily tests given
to No. 420 was increased to twenty.

Instead of taking space for the presentation of the daily records, I may
state the general results of the tests. Neither of the mice learned to
choose the right box by means of form discrimination. In fact, there was
absolutely no sign of discrimination at any time during the tests. This
result is as surprising as it is interesting. I could not at first believe
that the mice were unable to perceive the difference in the lighted areas,
but assumed that they were prevented from getting the outlines of the
areas by the blinding effect of the light. However, decreasing the
intensity of the illumination did not alter the result. According to the
indications of this experiment, the dancer's ability to perceive visual
form is extremely poor.

Thus far the purpose of our experiments has been to ascertain what the
dancer is enabled to do by sight. Suppose we now approach the problem of
the role of this sense by trying to find out what it can do without sight.

[Illustration: FIGURE 23.--Labyrinth B. _I_, entrance; _O_, exit; 1, 2, 3,
doorways between alleys.]

For the investigation of this matter the labyrinth method seemed eminently
suitable. The first form of labyrinth which was used in these visual tests
appears in ground plan in Figure 23. It was made of 1-1/2 cm. boards. The
length was 52 cm., the width 17 cm., the depth 10 cm. Each of the
doorways, _I_ (the entrance), 1, 2, 3, and _O_ (the exit), was 5 by 5 cm.
The alleys were 2-1/2 cm. wide. For this width the necessity is obvious
from what has already been said of the animal's propensity to whirl on all
occasions. As the mice almost never tried to climb up the walls, no cover
for the labyrinth was needed. The direct route is indicated by the symbols
_I_-1-2-3-_O_. If an error be defined as a choice of the wrong path as the
animal progressed toward the exit, five mistakes were possible in the
forward course: the first by turning to the left at the entrance; the
second by failing to pass through doorway 1; the third by turning to the
right after passing through doorway 1; the fourth by failing to pass
through doorway 3, and the fifth by turning to the left after passing
through 3. In case the mouse retraced its course, any mistakes made as it
again progressed towards _O_ were counted, as at first, no matter how many
times it went over the same ground. Thus an individual might make the same
mistake several times in the course of a single test in the labyrinth.

With this labyrinth Nos. 7, 998, 15, 16, 151, and 152 were tested. At
first a record was kept of the time which elapsed from the instant the
animal entered _I_ to the instant it emerged at _O_, of the path which it
followed, and of the number of errors which it made; but later only the
number of errors was recorded.



Labyrinth-B Experiments

NO. 7 NO. 998

1 June 16 66" 8 127" 19
2 16 11 0 94 12
3 16 15 2 18 3
4 16 7 0 13 2
5 16 5 0 10 1
6 18 61 15 12 3
7 18 13 3 14 4
8 18 14 5 8 1
9 18 24 9 16 2
10 18 10 1 9 1
11 19 36 13 80 17
12 19 8 3 10 1
13 19 6 1 7 1
14 19 9 1 8 0
15 19 12 2 7 0
16 20 14 1 25 0
17 20 28 3
18 20 No efforts No efforts
to escape to escape




Electric Shock given as Punishment for Mistakes

No. 7 No. 998

1 June 29 Light 4 Light 9
2 29 Light 1 Light 3
3 29 Light 1 Light 2
4 29 Light 0 Light 0
5 29 Light 0 Light 0
6 29 Light 0 Light 0
7 29 Light 1 Light 0
8 29 Light 0 Light 0
9 29 Light 1 Darkness 0
10 29 Light 1 Light 0
11 29 Light 1 Darkness 0
12 29 Light 0 Light 0
13 29 Light 0 Light 0
14 29 Light 0 Light 0
15 29 Light 0 Light 0
16 29 Light 0 Light 0
17 29 Darkness 2 Darkness 0
18 29 Light 2 Light 0
with paper
19 29 Light 0 Light 0
20 29 Darkness 0 Light 0
with paper
21 29 Light 0 Light 0
22 29 Light 0 Darkness 0
23 29 Light 0 Odorless 0
24 June 29 Light 0 Darkness 0
25 29 Light 0
26 29 Darkness 4
27 29 Light with
paper 1
28 29 Light 0
29 29 Light with
paper 1
30 29 Darkness 0
31 29 Odorless 2
32 29 Darkness 4

As the results in Table 31 show, the time and number of errors rapidly
diminished. Number 7, for example, made no errors in the second test. The
chiefly significant fact which appeared in these preliminary experiments,
however, was that the mice soon ceased to care whether they got out of the
labyrinth or not. After they knew the path perfectly, they would enter the
wrong passages repeatedly and wander about indefinitely. It was obvious,
therefore, that the labyrinth could not be used to reveal the role of
sight unless some sufficiently strong motive for continuous effort to
escape from it could be discovered. Naturally I looked to the electric
shock for aid.

The labyrinth of Figure 23, which for convenience in distinguishing it
from several other forms to be described later I have designated as
labyrinth B, was placed upon a board 90 cm. long and 30 cm. wide about
which had been wound two pieces of phosphor bronze wire after the manner
described on p. 94. At _O_, Figure 24, there was an opening closed by a
swinging door which led into a box 40 by 24 cm. In one corner of this box
was a small nest-box. The significance of this rearrangement of the
labyrinth is apparent. As in the preliminary tests, the dancer was started
at I, but instead of being allowed to wander about without any other
result than delay in escape, it was given a shock each time it made an
error. The satisfaction of escaping from the narrow bounds of the
labyrinth's passages, which alone was not strong enough to impel a dancer
constantly to do its best to escape, was thus supplemented by the powerful
and all-controlling tendency to avoid the disagreeable stimulus which
resulted from entering certain of the passages. The result of this
modification of method is strikingly exhibited by the data of Table 32.

[Illustration: Figure 24.--Labyrinth B on an interrupted circuit board.
_I_-1-2-3-_O_, labyrinth path; _B_, nest-box; _N_, nest; _EW_, board wound
with phosphor bronze wire; _IC_, induction apparatus; _C_ electric cell;
_K_, key.]

This table was constructed for the purpose of exhibiting the principal
features of the results obtained with labyrinth _B_ in certain preliminary
experiments in which the conditions were changed in various ways. Chief
among the important facts which appear in the illustrative data (for Nos.
7 and 998) which are presented, are the following. The dancers readily
learn the path of labyrinth B so that they can follow it quickly and with
perfect accuracy. After familiarity with the direct path from entrance to
exit has been gained, they become indifferent about escaping and tend to
wander aimlessly. The introduction of the electric shock as punishment for
the choice of the wrong passage impels them to do their best to avoid
errors. The path once learned can be followed in total darkness with few
or no errors. Table 32 indicates marked differences in the behavior of No.
7 and No. 998. The latter learned the path readily and was little
disturbed by any of the changes in conditions. In total darkness he
followed the path rapidly and accurately, as was indicated by the time of
the trip and the path that he left on a sheet of smoked paper that had
been placed on the floor of the labyrinth as a means of obtaining a record
of the errors made. The presence of the smoked paper did not seem to
interfere at all with his behavior, nor did the thorough washing of the
labyrinth and the resultant removal of its odors. In the case of No. 7 the
opposite was true. She did not learn the path readily, was confused by any
change in conditions, had great difficulty in finding her way in darkness,
made errors when the smoked paper was placed on the floor and after the
odors of the labyrinth had been removed by washing. Of the six dancers
which were observed in these preliminary tests, No. 7 alone gave
convincing evidence of the importance of sight.

I think we may say in the light of the results of the table that such
errors as appear in the darkness tests are due rather to the disturbing
influence of a change in the conditions of the experiment than to the
exclusion of visual data, for as many or more errors were sometimes caused
simply by changing the position of the labyrinth, placing smoked paper on
the floor, or by introducing a new odor at some point. The exclusion of
the possibility of guidance by smell and touch did not seriously interfere
with the animal's ability to follow the path.

The results which have just been considered seemed to be of sufficient
interest and importance to justify the further use of the labyrinth method
in the investigation of the role of vision. A series of experiments with
labyrinth B was therefore planned so that the importance of sight, touch,
and smell in connection with this form of habit should be more
satisfactorily exhibited. Does the dancer follow the path by sight, touch,
smell, by all, or by no one of them?

This series of tests with labyrinth B, whose several purposes may best be
explained in connection with the various kinds of tests enumerated below,
consisted of:

I. A preliminary test in which the dancer was permitted to wander about in
the labyrinth, without being shocked, until it finally escaped to the
nest-box by way of the exit. Thus the animal was given an opportunity to
discover that escape from the maze was possible.

II. This was immediately followed by a series of tests at the rate of
about one per minute, with an electric shock as punishment for every
mistake. This was continued without interruption until the path had been
followed without error five times in succession.

III. The labyrinth was now moved about 3 cm. to one side so that it
covered a new floor area, and a test was given for the purpose of
ascertaining whether the mouse had been following a trail on the floor.

IV. Tests with smoked paper on the floor were now alternated with tests in
which the floor was plain. The alternation was rendered necessary by the
fact that the paper was laid over the electric wires and therefore
prevented the punishment of mistakes. The purpose of these tests was to
discover whether the smoked paper, which was an essential condition for
the next test, was itself a disturbing condition. These tests were
continued until the animal had followed the path correctly, despite the
smoked paper, twice in succession.

V. The electric lights were now turned out and tests were given in total
darkness, with smoked paper on the floor as a means of obtaining a record
of the number of errors. These tests were continued until the path had
been followed once correctly.

VI. The labyrinth was now thoroughly washed with warm water, to which a
little kerosene had been added, and quickly dried over a steam radiator.
This usually necessitated a delay of about five minutes. As soon as the
labyrinth was dry, tests were given to discover whether the odors of the
various passages had been serving as important guiding conditions. These
tests were continued until the path had been followed once without error.

VII. A final test in darkness completed the series.

As it was not possible for the observer to watch the animal and thus to
count the number of mistakes which it made in total darkness, the simple
method of placing a piece of smoked paper on the floor of the labyrinth
was used. The mouse left a graphic record of its path on the paper and
from this the number of errors could be ascertained. In the tests now to
be described the smoked paper was placed upon the electric wires, but
later a form of electric labyrinth was devised in which it was underneath
and therefore did not interfere with the electric shock.

The above series of tests was given under the same external conditions in
a dark-room to six pairs of dancers. In all cases, two individuals, a male
and a female, which had been kept in the same cage, were experimented with
at the same time, _i.e._ one was permitted to rest in the nest-box while
the other was being put through a test. This was done in order that the
comparison of the results for males and females should be perfectly fair.

The detailed results of this long series of tests may be presented for
only two individuals, Nos. 210 and 215, Table 33. In this table lines
separate the results of the seven different kinds of tests.



No. 210 No. 215


I. 1 No shock 9 I. No shock 2

II. 2 Shock 5 II. Shock 3
3 Shock 4 Shock 1
4 Shock 2 Shock 0
5 Shock 3 Shock 0
6 Shock 0 Shock 0
7 Shock 0 Shock 0
8 Shock 0 Shock 0

9 Shock 0 III. Labyrinth 0

10 Shock 0 IV. Paper on floor 4

III. 11 Labyrinth 0 No paper (shock) 0

IV. 12 Paper on 0 0
13 No paper 0 No paper 0
14 Paper 1 Paper 1
15 No paper 0 No paper 0
16 Paper 7 Paper 4
17 No paper 0 No paper 0
18 Paper 0 Paper 0
19 No paper 0 No paper 0
20 Paper 4 Paper 0
21 No paper 0 No paper 0
22 Paper 2 V. Darkness 0
23 No paper 2 VI. Labyrinth 2
24 Paper 1 washed 0
25 No paper 0 VII. Darkness 2
26 Paper 0
27 No paper 0
28 Paper 0
29 No paper 0
V. 30 Darkness 0
VI. 31 Labyrinth 2
32 0
VII. 33 Darkness 0

The average results for the twelve individuals (six of each sex) which
were subjected to the tests, I have arranged in Table 34. The Roman
numerals at the top of the table designate the seven groups of tests, and
the figures under each, the numerical results of the tests. I may explain
and comment upon the averages of the several columns of this table in

Column I gives the number of errors made in the preliminary test.
Curiously enough, the males made many more errors than the females.

For the second group of tests (II) two results have been tabulated: the
number of the first correct test, and the total number of tests before the
path was followed correctly five times in succession. The first correct
trip came usually after not more than five or six tests, but five
successive correct trips demanded on the average at least fourteen
training tests.

Destruction of the floor path by movement of the labyrinth to one side,
without changing its relations to the points of the compass, disturbed the
mice very little. Only four of the twelve individuals made any mistakes as
a result of the change in the tactual conditions, and the average error as
it appears in Column III is only .3.



TEST. _____________________ MOVED. NO OF TIMES

210 9 5 9 0 9
212 2 3 8 1 3
214 6 10 28 0 22
220 25 4 8 0 14
410 11 6 20 0 10
420 14 6 14 1 7

AVERAGES 11.2 5.7 14.5 .3 10.8


211 16 6 10 1 5
213 7 5 14 1 21
215 2 3 7 0 6
225 14 6 18 0 14
415 6 6 13 0 3
425 10 7 13 0 8

AVERAGES 9.2 5.5 12.5 .3 9.5


210 0 1 2 0
212 2 2 0 0
214 0 1 -- 0
220 2 4 2 0
410 1 3 2 1
420 2 4 1 4

Averages 1.2 2.5 1.2 0.8


211 2 2 0 0
213 2 2 -- 3
215 0 1 2 2
225 3 2 0 0
415 1 3 2 1
425 1 7 0 0

Averages 1.5 2.8 0.7 1.0

That covering the floor with smoked paper forced the mice to relearn the
path, in large measure, is evident from the results of Column IV. An
average of ten tests was necessary to enable the mice to follow the path
correctly. It is almost certain, however, that the interference with the
perfectly formed labyrinth habit which this change in the condition of the
floor caused was not due to the removal of important tactual sense data.

As Column V shows, the number of errors in total darkness is very small.
Some individuals gave no sign of being disturbed by the absence of visual
guidance, others at first seemed confused. I have given in the table the
number of errors in the first darkness test and the number of the first
test in which no mistakes occurred.

No more disturbance of the dancer's ability to follow the path which it
had learned resulted from washing the labyrinth thoroughly than from
darkening the room. Indeed it is clear from Column VI that the path was
not followed by the use of smell. However, the test in darkness, after the
odor of the box had been removed, proved conclusively that in most cases
the mice could follow the path correctly without visual or olfactory

The behavior of 18 individuals as it was observed in labyrinth B makes
perfectly evident three important facts, (1) In following the path which
it has learned, the dancer in most instances is not guided to any
considerable extent by a trail (odor or touch) which has been formed by
its previous journeys over the route; (2) sight is quite unnecessary for
the easy and perfect execution of the labyrinth habit, for even those
individuals which are at first confused by the darkening of the experiment
room are able after a few tests to follow the path correctly; (3) and,
finally, smell, which according to current opinion is the chiefly
important sense of mice and rats, is not needful for the performance of
this habitual act.

At this point we may very fittingly ask, what sense data are necessary for
the guidance of the series of acts which constitutes the labyrinth habit?
I answer, probably none. A habit once formed, the senses have done their
part; henceforth it is a motor process, whose initiation is conditioned by
the activity of a receptive organ (at times a sense receptor), but whose
form is not necessarily dependent upon immediate impressions from eye,
nose, vibrissae, or even from internal receptors. These are statements of
my opinion; whether they express the truth, either wholly or in part, only
further experimentation can decide.

In considering the results of these labyrinth tests it is important that
we distinguish clearly those which have to do with the conditions of habit
formation from those which instead have to do with the conditions of habit
performance. Sense data which are absolutely necessary for the learning of
a labyrinth path may be of little or no importance for the execution of
the act of following the path after the learning process has been
completed. Thus far in connection with the labyrinth tests we have
discussed only the relations of sight, touch, and smell to what I have
called habit performance. We may now ask what part these senses play in
the formation of a labyrinth habit.

A very definite answer to this question is furnished by observation of the
behavior of the dancers in the tests. Most of them continuously made use
of their eyes, their noses, and their vibrissae. Some individuals used one
form of receptive organ almost exclusively. I frequently noticed that
those individuals which touched and smelled of the labyrinth passages most
carefully gave least evidence of the use of sight. It is safe to say,
then, that under ordinary conditions habit formation in the dancer is
conditioned by the use of sight, touch, and smell, but that these senses
are of extremely different degrees of importance in different individuals.
And further, that, although in the case of some individuals the loss of
sight would not noticeably delay habit formation, in the case of others it
would seriously interfere with the process. When deprived of one sense,
the dancer depends upon its remaining channels of communication with
environment. Indeed there are many reasons for inferring that if deprived
of sight, touch, and smell it would still be able to learn a labyrinth
path; and there are reasonable grounds for the belief that a habit once
formed can be executed in the absence of all special sense data.
Apparently the various receptive organs of the body furnish the dancer
with impressions which serve as guides to action and facilitate habit
formation, although they are not necessary for habit performance.

The reader may wonder why I have not carried out systematic experiments to
determine accurately and quantitatively the part which each sense plays in
the formation of a labyrinth habit instead of basing my inferences upon
incidental observation of the behavior of the dancers. The reason is
simply this: the number and variety of experiments which were suggested by
the several directions in which this investigation developed rendered the
performance of all of them impossible. I have chosen to devote my time to
other lines of experimentation because a very thorough study of the
conditions of habit formation has recently been made by Doctor Watson.[1]

[Footnote 1: Watson, J. B., _Psychological Review_, Monograph Supplement,
Vol. 8, No. 2, 1907.]

What is the role of sight in the dancing mouse? How shall we answer the
question? The evidence which has been obtained in the course of my study
of the animal indicates that brightness vision is fairly acute, that color
vision is poor, that although form is not clearly perceived, movement is
readily perceived. My observations under natural conditions justify the
conclusion that sight is not of very great importance in the daily life of
the dancer, and my observations under experimental conditions strongly
suggest the further conclusion that movement and changes in brightness are
the only visual conditions which to any considerable extent control the
activity of the animal.



Nearly all of the experiments described in earlier chapters have revealed
facts concerning the educability of the dancer. In order to supplement the
knowledge of this subject thus incidentally gained and to discover the
principles of educability, the specially devised experiments whose results
appear in this and succeeding chapters were arranged and carried out with
a large number of mice. In the work on the modifiability of behavior I
have attempted to determine (1) by what methods the dancer is capable of
profiting by experience, (2) the degree of rapidity of learning, (3) the
permanency of changes wrought in behavior, (4) the effect of one kind of
training upon others, (5) the relation of re-training to training, and (6)
the relation of all these matters to age, sex, and individuality.

As it is obvious that knowledge of these subjects is a necessary condition
for the intelligent appreciation of the capacities of an animal, as well
as of the choice of methods by which it may be trained advantageously,
perhaps it is not too much to expect that this investigation of the nature
and conditions of educability in the dancing mouse may give us some new
insight into the significance of certain aspects of human education and
may serve to suggest ways in which we may measure and increase the
efficiency of our educational methods.

Merely for the sake of convenience of description I shall classify the
methods which have been employed as problem methods, labyrinth methods,
and discrimination methods. That these names are not wholly appropriate is
suggested by the fact that discrimination necessarily occurs in connection
with each of them. As problem methods we may designate those tests of
initiative and modifiability which involve the opening of doors by pushing
or pulling them, and the climbing of an inclined ladder. An example of the
labyrinth method has been presented in Chapter XI. The name discrimination
method I have applied to those tests which involve the choice of one of
two visual, tactual, or olfactory conditions. The white-black
discrimination tests, for example, served to reveal the rapidity and
permanency of learning as well as the presence of brightness vision.

In the case of most mammals whose educability has been studied
experimentally, problem methods have proved to be excellent tests of
docility and initiative. The cat, the raccoon, the monkey, in their
attempts to obtain food, learn to pull strings, turn buttons, press
latches, slide bolts, pull plugs, step on levers. The dancer does none of
these things readily. Are we therefore to infer that it is less
intelligent, that it is less docile, than the cat, the raccoon, or the
monkey? Not necessarily, for it is possible that these methods do not suit
the capacity of the animal. As a matter of fact, all of the tests which
are now to be described in their relation to the educability of the dancer
bear witness to the importance of the selection of methods in the light of
the motor equipment and the habits of the animal which is to be tested.
Judged by ordinary standards, on the basis of results which it yields in
problem and labyrinth tests, the dancer is extremely stupid. But that this
conclusion is not justified is apparent when it is judged in the light of
tests which are especially adapted to its peculiarities.

Problems which are easy for other mammals because of their energetic and
persistent efforts to secure food in any way which their motor capacity
makes possible are useless as tests of the dancer's abilities, because it
is not accustomed to obtain its food as the result of strenuous and varied
activities. There are problems and problems; a condition or situation
which presents a problem to one organism may utterly lack interest for an
organism of different structure and behavior. What is a problem test in
the case of the cat or even of the common mouse, is not necessarily a
problem for the dancer. Similarly, in connection with the labyrinth
method, it is clear that the value of the test depends upon the desire of
the organism to escape from the maze. The cat, the rat, the tortoise do
their best to escape; the dancer is indifferent. Clearly, then, methods of
training should be chosen on the basis of a knowledge of the
characteristics of the animal whose educability is to be investigated.

The simplest possible test of the intelligence of the dancer which I could
devise was the following. Beside the cage in which the mice were kept I
placed a wooden box 26 cm. long, 23 cm. wide, and 12 cm. deep. Neither
this box nor the cage was covered, for the animals did not attempt to
climb out. As a way of passing from one of these boxes to the other I
arranged a ladder made of wire fly-screen netting. This ladder was about 8
cm. broad and it extended from the middle of one side of the wooden box
upward at an angle of about 30 deg. to the edge of the box and then descended
at the same angle into the cage.

A dancer when taken from the nest-box and placed in the wooden box could
return to its cage and thus find warmth, food, and company by climbing the
ladder. It was my aim to determine, by means of this apparatus, whether
the dancers can learn such a simple way of escape and whether they learn
by watching one another. As it turned out, a third value belonged to the
tests, in that they were used also to test the influence of putting the
mice through the act.

In the first experiment three dancers, Nos. 1000, 2, and 6, were together
placed in the wooden box. At the end of 15 minutes not one of them had
succeeded in returning to the cage. They were then driven to the bottom of
the ladder and started upward by the experimenter; with this assistance
all escaped to the nest-box. At the expiration of 5 minutes they were
again placed in the wooden box, whence the chilly temperature (about 60 deg.
F.) and the lack of food made them eager to return to their cage. No
attempt to climb up the ladder was made by any of them within 15 minutes,
so the experimenter directed them to the ladder and started them upward as
in the first test. This completed the experiment for the day. The
following day two tests were given in the same way. In the second of these
tests, that is, on its fourth trial, No. 1000 climbed over of his own
initiative in 5 minutes. The others had to be assisted as formerly. On the
third day No. 1000 found his way back to the nest-box quickly and fairly
directly, but neither No. 2 or No. 6 climbed of its own initiative in the
first test. When their movements were restricted to the region of the box
about the base of the ladder, both of them returned to the cage quickly.
And on the second test of the third day all the mice climbed the ladder

In Table 35 I have given the time required for escape in the case of 40
tests which were given to these 3 individuals at the rate of 2 tests per

When the time exceeded 15 minutes the mice were helped out by the
experimenter; a record of 15 minutes, therefore, indicates failure.
Naturally enough the motives for escape were not sufficiently strong or
constant to bring about the most rapid learning of which the dancer is
capable. Sometimes they would remain in the wooden box washing themselves
for several minutes before attempting to find a way of escape. On this
account I made it a rule to begin the time record with the appearance of
active running about. The daily average time of escape as indicated in the
table does not decrease regularly and rapidly. On the fourth day, which
was the first on which all three of the dancers returned to the cage by
way of the ladder of their own initiative in both tests, the average is
214 seconds. In contrast with this, on the twentieth day the time was only
5 seconds. It is quite evident that the dancers had learned to climb the

At the end of the twentieth day the experiment was discontinued with Nos.
2 and 6, and after two weeks they were given memory tests, which showed
that they remembered perfectly the ladder-climbing act, for when placed in
the wooden box, with Nos. 4 and 5 as controls, they returned to the cage
by way of the ladder immediately and directly.



Time in Minutes and Seconds

No. of Date No. 1000 No. 2 No. 6 Average Daily Av.
Exp. 1905 For All For All

1 Nov. 14 15' 15' 15' -- --
2 15' 15' 15' -- --

3 15 15' 15' 15' -- --
4 300" 15' 15' -- --

5 16 480" 15' 15' -- --
6 180" 300" 420" 300" 300"

7 17 450" 240" 540" 410"
8 20" 15" 18" 18" 214"

9 18 90" 180" 135" 135"
10 135" 105" 165" 135" 135"

11 19 480" 240" 330" 350"
12 30" 120" 90" 80" 143"

13 20 360" 75" 120" 185"
14 5" 6" 8" 6" 95"

15 21 105" 450" 120" 192"
16 8" 80" 20" 54" 123"

17 22 255" 300" 180" 245"
18 10" 30" 270" 103" 174"

19 23 300" 660" 450" 470"
20 90" 120" 150" 120" 295"

21 24 240" 125" 225" 197"
22 4" 6" 168" 59" 128"

23 Nov. 25 305" 85" 130" 173"
24 5" 6" 118" 43" 108"

25 26 3" 8" 44" 18"
26 19" 1" 176" 98" 58"

27 27 150" 79" 269" 166"
28 26" 3" 31" 20" 93"

29 28 214" 18" 267" 166"
30 40" 3" 4" 16" 91"

31 29 130" 45" 250" 142"
32 12" 3" 25" 13" 77"

33 Dec. 2 61" 35" 44" 47"
34 50" 5" 24" 26" 36"

35 3 66" 18" 2" 29"
36 8" 5" 10" 8" 19"

37 4 9" 4" 3" 5"
38 10" 5" 6" 7" 6"

39 5 5" 3" 5" 4"
40 10" 4" 3" 6" 5"

One of the most interesting and important features of the behavior of the
dancer in the ladder experiment was a halt at a certain point on the
ladder. It occurred just at the edge of the wooden box at the point where
the ladder took a horizontal position, and led over into the cage. Every
individual from the first test to the last made this halt. Although from
the point of view of the experimenter the act was valueless, it may have
originated as an attempt to find a way to escape from the uncomfortable
position in which the animal found itself on reaching the top of the
ladder. Its persistence after a way of escape had been found is an
indication of the nature of habit. Day after day the halt became shorter
until finally it was little more than a pause and a turn of the head
toward one side of the ladder. I think we may say that in this act we have
evidence of the persistence of a particular resolution of physiological
states which is neither advantageous nor disadvantageous to the organism.
Had the act resulted in any gain, it would have become more marked and
elaborate; had it resulted in injury or discomfort, it would have
disappeared entirely. I have observed the same kind of behavior in the
frog and in other animals. What the animal begins to do it persists in
unless the act is positively harmful or conflicts with some beneficial
activity. The only explanation of certain features of behavior is to be
found in the conditions of their original occurrence. They persist by
sheer force of conservatism. They have value only in the light of the
circumstances under which they first appeared. Although this is merely a
fact of habit formation, it suggests that many of the problems which have
puzzled students of behavior for ages may be solved by a study of the
history of activity.

That there are marked individual differences in intelligence in the
dancing mice is apparent from the results of the ladder-climbing
experiment. No. 1000 learned to climb quickly, and largely by his own
initiative; Nos. 2 and 6, on the contrary, learned only by reason of
tuition (being put through the required act by the experimenter). It
occurred to me that this experiment, since it was difficult for some
individuals and easy for others, might be used to advantage as a test of
imitation. If a dancer which knows how to escape to the cage by way of the
ladder be placed in the wooden box with one which, despite abundant
opportunity, has proved unable to form the habit on his own initiative,
will the latter profit by the activity of the former and thus learn the
method of escape?

On November 20, Nos. 4 and 5 were placed in the wooden box and left there
for half an hour. As they had failed to escape at the end of this
interval, they were taken out of the box by the experimenter and returned
to the nest-box. November 21 and 22 this test of their ability to learn to
climb the ladder was repeated with the same result. On November 23 they
were placed in the box with the three mice which had previously been
trained to climb the ladder. The latter escaped at once. Apparently the
attention of Nos. 4 and 5 was drawn to the ladder by the disappearance of
their companions, for they approached its foot and No. 5 climbed up a
short distance. Neither succeeded in escaping, however, and they made no
further efforts that day. On the 24th, and daily thereafter until the
29th, these two dancers were placed in the box for half an hour, with
negative results. At the end of the half hour on the 29th, Nos. 2 and 6
were placed in the box and permitted to go back and forth from one box to
the other repeatedly within sight of Nos. 4 and 5. The latter made no
attempts to follow them, although at times they seemed to be watching
their movements as they ascended the ladder.

To render the results of this test of imitation still more conclusive No.
5 was given further opportunity to learn from No. 1000. Beginning December
2, the following method of experimentation was employed with these two
individuals. They were placed in the wooden box together. No. 1000 usually
climbed out almost immediately. Sometimes No. 5 apparently saw him
disappear up the ladder; sometimes she paid no attention whatever either
to the presence or absence of her companion. After he had been in the
nest-box for a few seconds, No. 1000 was returned to the wooden box by the
experimenter and again permitted to climb out for the benefit of No. 5.
This mode of procedure was kept up until No. 1000 had made from three to
ten trips. No. 5 was left in the box for half an hour each day. This test
was repeated on 18 days within a period of 3 weeks. No. 5 showed no signs
of an imitative tendency, and she did not learn to climb the ladder.

To this evidence of a lack of an imitative tendency in the dancer I may
here add the results of my observations in other experiments. In the
discrimination tests and in the labyrinth tests I purposely so arranged
conditions, in certain instances, that one individual should have an
opportunity to imitate another. In no case did this occur. Seldom indeed
did the animals so much as follow one another with any considerable degree
of persistence. They did not profit by one another's acts.

Excellent evidence in support of this conclusion was furnished by the
behavior of the mice in the discrimination experiments. Some individuals
learned to pull as well as to push the swinging wire doors of the
apparatus and were thus enabled to pass through the doorways in either
direction; other individuals learned only to pass through in the direction
in which the doors could be pushed open. Naturally I was interested to
discover whether those which knew only the trick of opening the doors by
pushing would learn to pull the doors or would be stimulated to try by
seeing other individuals do so. At first I arranged special tests of
imitation in the discrimination box; later I observed the influence of the
behavior of one mouse upon that of its companion in connection with visual
discrimination experiments. This was made possible by the fact that
usually a pair of individuals was placed in the discrimination box and the
tests given alternately to the male and to the female. Both individuals
had the freedom of the nest-box and each frequently saw the other pass
through the doorway between the nest-box, _A_, and the entrance chamber,
_B_ (Figure 14), either from _A_ to _B_ by pushing the swing door or from
_B_ to _A_ by pulling the door.

Although abundant opportunity for imitation in connection with the opening
of the doors in the discrimination box was given to twenty-five
individuals, I obtained no evidence of ability to learn by imitation. The
dancers did not watch the acts which were performed by their companions,
and in most instances they did not attempt to follow a mate from nest-box
to entrance chamber.

These problem tests, simple as they are, have revealed two important facts
concerning the educability of the dancer. First, that it does not learn by
imitation to any considerable extent, and, second, that it is aided by
being put through an act. Our general conclusion from the results of the
experiments which have been described in this chapter, if any general
conclusion is to be drawn thus prematurely, must be that the dancing mouse
in its methods of learning differs markedly from other mice and from rats.



The problem method, of which the ladder and door-opening tests of the
preceding chapter are examples, has yielded interesting results concerning
the individual initiative, ingenuity, motor ability, and ways of learning
of the dancer; but it has not furnished us with accurate measurements of
the rapidity of learning or of the permanency of the effects of training.
In this chapter I shall therefore present the results of labyrinth
experiments which were planned as means of measuring the intelligence of
the dancer.

The four labyrinths which have been used in the investigation may be
designated as _A, B, C,_ and _D_. They differ from one another in the
character of their errors, as well as in the number of wrong choices of a
path which the animal might make on its way from entrance to exit. In the
use of the labyrinth method, as in the case of the discrimination method
of earlier chapters, the steps by which a satisfactory form of labyrinth
for testing the dancer was discovered are quite as interesting and
important for those who have an intelligent appreciation of the problems
and methods of animal psychology as are the particular results which were
obtained. For this reason, I shall describe the various forms of labyrinth
in the order in which they were used, whether they proved satisfactory or
not. At the outset of this part of my investigation, it was my purpose to
compare directly the capacity for habit formation in the dancer with that
of the common mouse. This proved impracticable because the same labyrinth
is not suited to the motor tendencies of both kinds of mice.

[Illustration: FIGURE 25.--Labyrinth A. _I_. entrance; _O_, exit; 1, 2, 3,
4, blind alleys.]

The first of the four labyrinths, A, appears in ground plan in Figure 25.
It was constructed of wood, as were the other labyrinths also, and
measured 60 cm. in length and width, and 10 cm. in depth. The outside
alleys were 5 cm. wide. In the figure, _I_ marks the starting point or
entrance to the maze, and _O_ the exit through which the mouse was
permitted to pass into its nest-box. Any turn in the wrong direction which
the animal made in its progress from entrance to exit was recorded as an
error. The four errors, exclusive of the mistake of turning back, which
were possible in this labyrinth, are indicated in the figure by the
numerals 1, 2, 3, and 4. By retracing its steps a mouse might repeat any
one or all of these errors, and add to them the error of turning back.

In the experiments a mouse was permitted to enter the maze from a small
box which had been placed by the experimenter at _I_, and an accurate
record was kept of the number of errors which it made in finding its way
from entrance to exit, and of the time occupied. Each of five dancers was
given 31 tests in this labyrinth. The number of tests per day varied, as
is indicated in Table 36, from 1 to 4. The results of the tests, so far as
errors and times are in question, appear in the table. _T_ at the head of
a column is an abbreviation for time, _E_ for errors.

The dancers did not learn to escape from this labyrinth easily and
quickly. In fact, the average time of the thirty-first test (198") is
considerably longer than that of the first (130"). The number of errors
decreased, it is true, but even for the last test it was 6.6 as compared
with only a little more than twice that number for the first test. The
last column of the table furnishes convincing proof of the truth of the
statement that the animals did not acquire a perfect labyrinth-A habit.
Was this due to inability to learn so complex a path, or to the fact that
the method is not adapted to their nature? Observation of the behavior of
the mice in the experiments enables me to say with certainty that there
was no motive for escape sufficiently strong to establish a habit of
following the direct path. Often, especially after a few experiences in
the maze, a dancer would wander back and forth in the alleys and central
courts, dancing much of the time and apparently exploring its surroundings
instead of persistently trying to escape. This behavior, and the time and
error results of the accompanying table, lead me to conclude that the
labyrinth method, as it has been employed in the study of the intelligence
of several other mammals, is not a satisfactory test of the ability of the
dancer to profit by experience. That the fault is not in the labyrinth
itself is proved by the results which I obtained with common mice.



TEST DATE No. 1000 No. 2 No. 6 No. 4 No. 5 FOR ALL

1 Nov 23 130" 14 100" 8 170" 13 60" 6 190" 26 130" 13.4
2 24 140 19 78 7 60 8 149 6 211 25 128 13.0
3 25 392 31 87 1 98 5 185 13 120 9 176 11.8
4 26 448 38 38 3 47 2 50 3 121 12 141 11.3
5 27 142 8 21 2 27 3 27 2 17 1 47 3.2
6 28 45 2 61 7 63 5 102 8 33 4 61 5.2
7 29 303 17 64 7 36 3 42 2 57 4 100 6.6
8 30 222 15 26 2 37 5 42 3 7 0 67 5.0
9 Dec 1 185 9 36 5 48 3 63 3 94 8 85 5.6
10 2 52 2 71 4 19 0 196 5 95 11 87 4.4
11 3 180 8 32 2 107 4 52 3 38 4 82 4.2
12 4 310 10 133 11 65 3 242 6 125 6 175 7.2
13 4 153 9 335 55 130 10 195 15 154 18 193 21.4
14 5 330 7 69 2 42 2 201 6 130 10 154 5.4
15 5 287 7 34 4 61 4 136 7 25 2 109 4.8
16 5 455 15 65 4 25 0 110 8 160 15 183 8.4
17 6 120 15 280 9 33 0 168 4 39 2 128 6.0
18 6 120 4 164 10 81 4 101 5 85 4 110 5.4
19 6 132 12 78 7 110 6 40 2 151 12 102 7.8
20 7 258 10 223 16 33 1 92 5 37 1 129 6.6
21 7 110 7 23 3 44 4 20 4 305 23 100 8.2
22 7 100 4 60 8 167 15 44 7 58 4 86 7.6
23 8 43 1 179 7 356 6 34 3 65 3 135 4.0
24 8 92 5 56 5 42 3 17 1 23 1 46 3.0
25 9 85 5 114 3 62 3 129 8 31 0 84 3.8
26 9 30 2 36 4 109 15 12 1 34 2 44 4.8
27 9 69 5 40 4 85 6 36 3 16 1 49 3.8
28 10 169 7 80 3 28 0 142 5 35 2 89 3.4
29 10 155 5 266 8 91 5 27 0 37 2 115 4.0
30 10 29 1 25 2 124 14 83 6 111 12 74 7.0
31 10 465 6 208 8 95 3 65 3 159 13 198 6.6

On the basis of two tests per day, two common mice, a white one and a gray
one, quickly learned to escape from labyrinth _A_ by the shortest path.
The time of escape for the gray individual (Table 37) decreased from 180"
in the first test to 21" in the tenth, and the number of errors from 6 to
1. Similarly in the case of the white individual, the time decreased from
122" to 8", and the errors from 5 to 1. A fraction of the number of tests
to which the dancer had been subjected sufficed to establish a habit of
escape in the common mouse. It is evident, therefore, that the dancer
differs radically from the common mouse in its behavior in a maze, and it
is also clear that the labyrinth method, if it is to be used to advantage,
must be adapted to the motor tendencies of the animal which is to be




1 180" 6 122" 5
2 26 2 80 6
3 37 1 56 4
4 18 0 27 1
5 68 2 33 2
6 10 1 19 1
7 11 1 17 1
8 13 1 17 1
9 10 0 8 1
10 21 1 8 1

The behavior of the dancer made obvious two defects in labyrinth A. Its
passages are so large that the mouse is constantly tempted to dance, and
it lacks the basis for a strong and constant motive of escape by the
direct path. To obviate these shortcomings labyrinth B was constructed, as
is shown in Figures 23 and 24, with very narrow passages, and a floor
which was covered with the wires of an interrupted electric circuit so
that errors might be punished. The length of this labyrinth was 52 cm. and
the passages were 2.5 cm. wide and 10 cm. deep. Dancing in these narrow
alleys was practically impossible, for the mice could barely turn around
in them. In the case of all except the common mice and two dancers, a
depth of 10 cm. was sufficient to keep the animals in the maze without the
use of a cover.

As an account of the behavior of the dancer in labyrinth B has already
been given in Chapter XI, I may now state the general results of the
experiments. In all, thirty individuals were trained in this labyrinth.
Each individual was given tests at the rate of one per minute until it had
succeeded in following the correct path five times in succession. The weak
electric shock, which was given as a punishment for mistakes, provided an
activity-impelling motive for escape to the nest-box.

An idea of the extreme individual difference in the rapidity with which
the labyrinth-B path was learned by these dancers may be obtained by an
examination of Table 38, from which it appears that the smallest number of
training tests necessary for a successful or errorless trip through the
maze was one and the largest number fourteen. It is to be remembered that
each mouse was given an opportunity to pass through the labyrinth once
without punishment for errors, and thus to discover, before the training
tests were begun, that a way of escape existed. This first test we may
designate as the preliminary trial. Table 38 further indicates that the
females acquired the labyrinth habit more quickly than did the males.





76 8 14 75 4 15
78 5 20 77 7 11
86 13 22 87 12 22
58 2 14 49 1 5
50 6 23 57 3 20
60 13 37 59 14 28
410 6 20 415 4 13
220 4 8 225 6 18
212 3 7 211 6 10
214 10 28 213 5 14

AV. 7.0 19.3 AV. 6.2 15.6

A graphic representation of certain of the important features of the
process of formation of the labyrinth-B habit is furnished by Figure 26 in
which the solid line is the curve of learning for the ten males of Table
38, and the broken line for the ten females. These two curves were plotted
from the number of errors made in the preliminary trial (P in the figure)
and in each of the subsequent tests up to the sixteenth. In the case of
both the males and the females, for example, the average number of errors
in the preliminary trial was 11.3, as is indicated by the fact that the
curves start at a point whose value is given in the left margin as 11.3.
In the second training test the number of errors fell to 3.3 for the males
and 2.7 for the females. The number of the test is to be found on the base
line; the number of errors in the left margin. If these two curves of
learning were carried to their completion, that for the males would end
with the thirty-seventh test, and that for the females with the twenty-

[Illustration: FIGURE 26.--Curves of habit formation, plotted from the
data of labyrinth-B tests with ten males and ten females. The figures in
the left margin indicate the number of errors; those below the base line
the number of the test. _P_ designates the preliminary test. Males
____[solid line]; Females ----[broken line].]

Time records are not reported for these and subsequent labyrinth tests
because they proved to be almost valueless as measures of the rapidity of
habit formation. At any point in its progress through a labyrinth, the
dancer may suddenly stop to wash its face, look about or otherwise examine
its surroundings; if a shock be given to hurry it along it may be
surprised into an error. It is my experience, and this is true of other
animals as well as of the dancing mouse, that a long trip, as measured in
time units, does not necessarily indicate the lack of ability to follow
the labyrinth path correctly and rapidly. Hence, whenever it is possible
(and the experimenter can always plan his tests so that it shall be
possible), the number of errors should be given first importance and the
time of the test second place. I have presented in Table 38 the number of
the first correct test, and the number of the last of five successive
correct tests. Space cannot be spared for records of the errors made in
the several tests by each individual.

In general, labyrinth B proved very satisfactory as a means of testing the
ability of the dancer to learn a simple path. The narrow passages
effectively prevented dancing, and the introduction of the electric shock
as a punishment for mistakes developed a motive for escape which was
uniform, constant, and so strong that the animals clearly did their best
to escape from the labyrinth quickly and without errors. This maze was so
simple that it did not tend to discourage them as did the one which is
next to be described. It must be admitted, however, that, though labyrinth
B is perfectly satisfactory as a test of the dancer's ability to learn to
follow a simple path, it is not an ideal means of measuring the rapidity
of habit formation. This is due to the fact that the preliminary trial and
the first training test play extremely different roles in the case of
different individuals. A dancer which happens to follow the correct path
from entrance to exit in the preliminary trial may continue to do so, with
only an occasional error, during several of the early training tests, and
it may therefore fail for a considerable time to discover that there are
errors which should be avoided. The learning process is delayed by its
accidental success. On the other hand, an individual which happens to make
many mistakes to begin with immediately attempts to avoid the points in
the maze at which it receives the electric shock. I was led to conclude,
as a result of the labyrinth-B experiments, that the path was too easy,
and that a more complex labyrinth would, in all probability, furnish a
more satisfactory means of measuring the rapidity of habit formation.

[Illustration: FIGURE 27--A record sheet, showing the plan of labyrinth C
(as made on the sheet by means of a rubber stamp) on which the
experimenter recorded the path followed by the mouse. This sample sheet
presents the path records for the first, fifth, tenth, and eleventh tests
of No. 2 in labyrinth C. 1, 2, 3, 4, 5 designate the several errors of the

On the basis of the supposition that a maze whose path was so complex that
the animal would not be likely to follow it correctly in the early trials
would be more to the purpose than either A or B, labyrinth C was devised.
As is shown in the plan of this maze, Figure 27, five mistakes in choice
of path were possible on the forward trip. These errors, as a rule, were
more difficult for the dancers to avoid than those of labyrinths A and B.
Those which are designated by the numerals 2, 3, and 4 were especially
difficult. Error 4 was much more troublesome for left whirlers than for
right whirlers because, after turning around abruptly at the entrance to
the blind alley, the former type of dancer almost always followed the side
wall of the maze so far that it missed the correct path. Undoubtedly the
various errors are not of the same value for different individuals; but it
would be extremely difficult, if not impossible, to devise a maze which
should be equally difficult for several normal individuals.

In order that records of the path followed by a mouse in test after test
might be kept with ease and accuracy by the experimenter, the plan of this
labyrinth, and also that of labyrinth D, were cast in rubber. The outlines
of labyrinths C and D which appear in Figures 27 and 28 respectively were
made with the rubber stamps which were thus obtained. Figure 27 is the
reproduction of a record sheet which presents the results of the first,
the fifth, the tenth, and the eleventh tests of No. 2 in labyrinth C. The
path followed by this individual in the first test was far too complex to
be traced accurately on the record sheet. The record therefore represents
merely the number of errors which was made in each region of the maze. For
the fifth test, and again for the tenth and the eleventh, the path was
recorded accurately. This simple device for making record blanks which can
readily be filled in at the time of the experiment should recommend itself
to all students of animal behavior.

In labyrinth C ten pairs of dancers were given continuous training tests
at the rate of one test per minute until they were able to follow the
direct path correctly. Because of the difficulty in learning this maze
perfectly, it was not demanded of the mice that they should follow the
path correctly several times in succession, but instead the training was
terminated after the first successful trip.





2 11 29 15
30 33 49 34
50 49 57 15
52 22 59 15
58 16 215 10
60 17 415 10
76 3 75 8
78 6 77 11
86 5 87 9
88 25 85 11

AV. 18.7 AV. 13.8

The results of the experiments with this labyrinth as they are presented
in Table 39 indicate that its path is considerably more difficult for the
dancer to learn than that of labyrinth B, that the females learn more
quickly than the males, and finally, that individual differences are just
as marked as they were in the case of the simpler forms of labyrinth. It
therefore appears that increasing the complexity of a labyrinth does not,
as I had supposed it might, diminish the variability of the results.
Certain of the individual differences which appear in Table 39 are due,
however, to the fact that in some cases training in labyrinth B had
preceded training in labyrinth C, whereas in the other cases C was the
first labyrinth in which the animals were tested. But even this does not
serve to account for the wide divergence of the results given by No. 2 and
No. 50, for the latter had been trained in B previous to his training in
C, and the former had not been so trained. Yet, despite the advantage
which previous labyrinth experience gave No. 50, he did not learn the path
of C as well in fifty tests as No. 2 did in eleven. The facts concerning
the value of training in one form of labyrinth for the learning of
another, as they were revealed by these experiments, may more fittingly be
discussed in a later chapter in connection with the facts of memory and

[Illustration: FIGURE 28.--Plan of Labyrinth _D_, as reproduced from a
print made with a rubber stamp. _I_, entrance; _O_, exit; numerals 1 to
13, errors.]

Labyrinth C is a type of maze which might properly be described as
irregular, since the several possible errors are extremely different in
nature. In view of the results which this labyrinth yielded, it seemed
important that the dancer be tested in a perfectly regular maze of the
labyrinth-D type. The plan which I designed as a regular labyrinth has
been reproduced, from a rubber stamp print, in Figure 28. As is true also
of the mazes previously described, it provides four kinds of possible
mistakes: namely, by turning to the left (errors 1, 5, 9, and 13), by
turning to the right (errors 3, 7, and 11), by moving straight ahead
(errors 2, 4, 6, 8, 10, and 12), and by turning back and retracing the
path just followed. The formula for the correct path of _D_ is simple in
the extreme, in spite of the large number of mistakes which are possible,
for it is merely "a turn to the right at the entrance, to the left at the
first doorway, and thereafter alternately to the right and to the left
until the exit is reached." This concise description would enable a man to
find his way out of such a maze with ease. Labyrinth D had been
constructed with an exit at 10 so that it might be used as a nine-error
maze if the experimenter saw fit, or as a thirteen-error maze by the
closing of the opening at 10. In the experiments which are now to be
described only the latter form was used.

Can the dancer learn a regular labyrinth path more quickly than an
irregular one? Again, I may give only a brief statement of results. Each
of the twenty dancers, of Table 40, which were trained in labyrinth D had
previously been given opportunity to learn the path of C, and most of them
had been trained also in labyrinth B. All of them learned this regular
path with surprising rapidity. The numerical results of the tests with
labyrinths B, C, and D, as well as the behavior of the mice in these
several mazes, prove conclusively that the nature of the errors is far
more important than their number. Labyrinth D with its thirteen chances of
error on the forward trip was not nearly as difficult for the dancer to
learn to escape from as labyrinth C with its five errors. That the
facility with which the twenty individuals whose records are given in
Table 40 learned the path of D was not due to their previous labyrinth
experience rather than to the regularity of the maze is proved by the
results which I obtained by testing in D individuals which were new to
labyrinth experiments. Even in this case, the number of tests necessary
for a successful trip was seldom greater than ten. If further evidence of
the ease with which a regular labyrinth path may be followed by the dancer
were desired, it might be obtained by observation of the behavior of an
individual in labyrinths C and D. In the former, even after it has learned
the path perfectly, the mouse hesitates at the doorways from time to time
as if uncertain whether to turn to one side or go forward; in the latter
there is seldom any hesitation at the turning points. The irregular
labyrinth is followed carefully, as by choice of the path from point to
point; the regular labyrinth is followed in machine fashion,--once
started, the animal dashes through it.





2 3 7 29 10 11
58 7 10 49 7 8
30 9 10 57 3 6
60 10 14 215 6 10
402 10 11 415 7 8
76 4 7 75 4 13
78 4 5 77 11 12
86 3 9 87 4 9
88 4 8 85 3 4
90 7 8 83 4 7

Av. 6.1 8.9 Av. 5.9 8.8

From the results of these labyrinth experiments with dancers I am led to
conclude that a standard maze for testing the modifiability of behavior of
different kinds of animals should be constructed in conformity with the
following suggestions. Errors by turning to the right, to the left, and by
moving forward should occur with equal frequency, and in such order that
no particular kind of error occurs repeatedly in succession. If we should
designate these three types of mistake by the letters _r, l_, and _s_
respectively, the error series of labyrinth C would read _l-l-r-s-l_. It
therefore violates the rule of construction which I have just formulated.
In the case of labyrinth D the series would read _l-s-r-s-l-s-r-s-l-s-r-s-
l_. This also fails to conform with the requirement, for there are three
errors of the first type, four of the second, and six of the third. Again,
in a standard maze, the blind alleys should all be of the same length, and
care should be taken to provide a sufficiently strong and uniform motive
for escape. In the case of one animal the desire to escape from
confinement may prove a satisfactory motive; in the case of another, the
desire for food may conveniently supplement the dislike of confinement;
and in still other cases it may appear that some form of punishment for
errors is the only satisfactory basis of a motive for escape. Readers of
this account of the behavior of the dancing mouse must not infer from my
experimental results that the electric shock as a means of forcing
discrimination will prove satisfactory in work with other animals or even
with all other mammals. As a matter of fact it has already been proved by
Doctor G. van T. Hamilton that the use of an electric shock may so
intimidate a dog that experimentation is rendered difficult and of little
value. And finally, in connection with this discussion of a standard
Labyrinth, I wish to emphasize the importance of so recording the results
of experiments that they may be interpreted in terms of an animal's
tendency to turn to the right or to the left. My work with the dancer has
clearly shown that the avoidance of a particular error may be extremely
difficult for left whirlers and very easy for right whirlers.

I hope I have succeeded in making clear by the foregoing account of my
experiments that the labyrinth method is more satisfactory in general than
the problem method as a means of measuring the rapidity of habit formation
in the dancer, and I hope that I have made equally clear the fact that it
is very valuable as a means of discovering the roles of the various senses
in the acquirement of a habit (Chapter XI). From my own experience in the
use of the labyrinth with the dancer and with other animals, I am forced
to conclude that its chief value lies in the fact that it enables the
experimenter so to control the factors of a complex situation that he may
readily determine the importance of a given kind of sense data for the
formation or the execution of a particular habit. As a means of measuring
the intelligence of an animal, of determining the facility with which it
is capable of adjusting itself to new environmental conditions, and of
measuring the permanency of modifications which are wrought in its
behavior by experimental conditions, I value the labyrinth method much
less highly now than I did previous to my study of the dancer. It is
necessarily too complex for the convenient and reasonably certain
interpretation of results. Precisely what is meant by this statement will
be evident in the light of the results of the application of the
discrimination method to the dancer, which are to be presented in the next
chapter. The labyrinth method is an admirable means of getting certain
kinds of qualitative results; it is almost ideal as a revealer of the role
of the senses, and it may be used to advantage in certain instances for
the quantitative study of habit formation and memory. Nevertheless, I
think it may safely be said that the problem method and the discrimination
method are likely to do more to advance our knowledge of animal behavior
than the labyrinth method.



Discrimination is demanded of an animal in almost all forms of the problem
and labyrinth methods, as well as in what I have chosen to call the
discrimination method. In the latter, however, discrimination as the basis
of a correct choice of an electric-box is so obviously important that it
has seemed appropriate to distinguish this particular method of measuring
the intelligence of the dancer from the others which have been used, by
naming it the discrimination method.

It has been shown that neither the problem nor the labyrinth method proves
wholly satisfactory as a means of measuring the rapidity of learning, or
the duration of the effects of training, in the case of the dancer. The
former type of test serves to reveal to the experimenter the general
nature of the animal's capacity for profiting by experience; the latter
serves equally well to indicate the parts which various receptors (some of
which are sense organs) play in the formation and execution of habits. But
neither of them is sufficiently simple, easy of control, uniform as to
conditions which constitute bases for activity, and productive of
interpretable quantitative results to render it satisfactory. The problem
method is distinctly a qualitative method, and, in the case of the dancing
mouse, my experiments have proved that the labyrinth method also yields
results which are more valuable qualitatively than quantitatively. I had
anticipated that various forms of the labyrinth method would enable me to
measure the modifiability of behavior in the dancer with great accuracy,
but, as will now be made apparent, the discrimination method proved to be
a far more accurate method for this purpose.

Once more I should emphasize the fact that my statements concerning the
value of methods apply especially to the dancing mouse. Certain of the
tests which have proved to be almost ideal in my study of this peculiar
little rodent would be useless in the study of many other mammals. An
experimenter must work out his methods step by step in the light of the
daily results of patient and intelligent observation of the motor
capacity, habits, instincts, temperament, imitative tendency,
intelligence, hardihood, and life-span of the animal which he is studying.
The fact that punishment has proved to be more satisfactory than reward in
experiments with the dancer does not justify the inference that it is more
satisfactory in the case of the rat, cat, dog, or monkey. Methods which
yielded me only qualitative results, if applied to other mammals might
give accurate quantitative results; and, on the other hand, the
discrimination method, which has proved invaluable for my quantitative
work, might yield only qualitative results when applied to another kind of

The form of the discrimination method whose results are to be presented in
this chapter has already been described as white-black discrimination. In
the discrimination box (Figures 14 and 15, p. 92) the two electric-boxes
which were otherwise exactly alike in appearance were rendered
discriminable for the mouse by the presence of white cardboards in one and
black cardboards in the other. In order to escape from the narrow space
before the entrances to the two electric-boxes, the dancer was required to
enter the white box. If it entered the black box a weak electric shock was
experienced. After two series of ten tests each, during which the animal
was permitted to choose either the white or the black box without shock or
hindrance, the training was begun. These two preliminary series serve to
indicate the natural preference of the animal for white or black previous
to the training. An individual which very strongly preferred the white
might enter, from the first, the box thus distinguished, whereas another
individual whose preference was for the black might persistently enter the
black box in spite of the disagreeable shocks. First of all, therefore,
the preliminary tests furnish a basis for the evaluation of the results of
the subsequent training tests. On the day succeeding the last series of
preliminary tests, and daily thereafter until the animal had acquired a
perfect habit of choosing the white box, a series of training tests was
given. These experiments were usually made in the morning between nine and
twelve o'clock, in a room with south-east windows. The entrances to the
electric-boxes faced the windows, consequently the mouse did not have to
look toward the light when it was trying to discriminate white from black.
All the conditions of the experiment, including the strength of the
current for the shock, were kept as constant as possible.

Choice by position was effectively prevented, as a rule, by shifting the
cardboards so that now the left now the right box was white. The order of
these shifts for the white-black series whose results are quantitatively
valuable appear in Table 12 (p. III). That the order of these changes in
position may be criticised in the light of the results which the tests
gave, I propose to show hereafter in connection with certain other facts.
The significant point is that the defects which are indicated by the
averages of thousands of tests could not have been predicted with
certainty even by the most experienced investigator in this field.

In Table 41 are to be found the average number of errors in each series of
ten white-black discrimination tests for five males and for five females
which were trained by being given ten tests per day, and similarly for the
same number of individuals of each sex, trained by being given twenty
tests per day. Since the results for these two conditions of training are
very similar, the averages for the twenty individuals are presented in the
last column of the table. For the present we may neglect the interesting
individual, sex, and age differences which these experiments revealed and
examine the significant features of the general averages, and of the
white-black discrimination curve (Figure 29).





A 5.8 6.0 5.9 5.8 5.8 5.8 5.85
B 5.6 6.2 5.9 5.8 5.6 5.7 5.8
1 5.0 5.0 5.0 5.6 4.6 5.1 5.05
2 2.6 4.6 3.6 4.4 5.0 4.7 4.15
3 3.0 3.4 3.2 3.4 3.4 3.4 3.3
4 2.6 3.8 3.2 2.4 2.2 2.3 2.75
5 2.4 2.0 2.2 2.6 1.8 2.2 2.2
6 1.6 1.6 1.6 1.0 2.2 1.6 1.6
7 1.0 1.4 1.2 2.0 0.4 1.2 1.2
8 0.2 0.6 .4 1.4 1.6 1.5 .95
9 0.2 1.0 .6 0.6 0.8 .7 .65
10 0 .8 .4 1.0 0.8 .9 .65
11 0 .8 .4 0.8 0 .4 .40
12 0 .6 .3 0.4 0 .2 .25
13 0 0 0 0 0 0 0
14 0 0 0 0 0 0
15 0 0 0 0 0 0

[Illustration: FIGURE 29.--Error curve plotted from the data given by
twenty dancers in white-black discrimination tests. The figures in the
left margin indicate the number of errors; those below the base line, the
number of the series. _A_ and _B_ designate the preference series.]

The preference series, _A_ and _B_, reveal a constant tendency to choose
the black box, whose strength as compared with the tendency to choose the
white box is as 5.8 is to 4.2. In other words, the dancer on the average
chooses the black box almost six times in ten. The first series of
training tests reduced this preference for black to zero, and succeeding
series brought about a rapid and fairly regular decrease in the number of
errors, until, in the thirteenth series, the white was chosen every time.
Since I arbitrarily define a perfect habit of discrimination as the
ability to choose the right box in three successive series of ten tests
each, the tests ended with the fifteenth series.

The discrimination curve, Figure 29, is a graphic representation of the
general averages of Table 41.--It is an error curve, therefore. Starting
at 5.85 for the first preliminary series, it descends to 5.8 for the
second series, and thence abruptly to 5.05 for the first training series.
This series of ten tests therefore served to reduce the black preference
very considerably. The curve continues to descend constantly until the
tenth series, for which the number of errors was the same as for the
preceding series, .65. This irregularity in the curve, indicative, as it
would appear, of a sudden cessation in the learning process, demands an
explanation. My first thought was that an error in computation on my part
might account for the shape of the curve. The error did not exist, but in
my search for it I discovered what I now believe to be the cause of the
interruption in the fall of the error curve. In all of the training series
up to the tenth the white cardboard had been on the right and the left
alternately or on one side two or three times in succession, whereas in
the tenth series, as may be seen by referring to Table 12 (p.111), it was
on the left for the first four tests, then on the right four times, and,
finally, on the left for the ninth test and on the right for the tenth.
This series was therefore a decidedly more severe test of the animal's
ability to discriminate white from black and to choose the white box
without error than were any that had preceded it. If my interpretation of
the results is correct, it was so much more severe than the ninth series
that the process of habit formation was obscured. It would not be fair to
say that the mouse temporarily ceased to profit by its experience; instead
it profited even more than usually, in all probability, but the
unavoidably abrupt increase in the difficultness of the tests was just
sufficient to hide the improvement.

As I have suggested, the plan of experimentation may be criticised
adversely in the light of this irregularity in the error curve. Had the
conditions been perfectly satisfactory the curve would not have taken this
form. I admit this, but at the same time I am glad that I chose that
series of shifts in the position of the cardboards which, as it happens,
served to exhibit an important aspect of quantitative measures of the
modifiability of behavior that otherwise would not have been revealed. Our
mistakes in method often teach us more than our successes. I have taken
pains, therefore, to describe the unsatisfactory as well as the
satisfactory steps in my study of the dancer.

[Illustration: FIGURE 30.--Error curve plotted from the data given by
thirty dancers, of different ages and under different conditions of
training, in white-black discrimination tests.]

The form of the white-black discrimination curve of Figure 29 is more
surprising than disappointing to me, for I had anticipated many more
irregularities than appear. What I had expected, as the result of training
five or even ten pairs of mice, was the kind of curve which is presented,
for contrast with the one already discussed, in Figure 30. This also is an
error curve, but, unlike the previous one, it is based upon results which
were got from individuals of different ages which were trained according
to the following different methods. Ten of these individuals were given
two or five tests daily, ten were given ten tests daily, and ten were
given twenty tests daily. The form of the curve serves to call attention
to the importance of uniform conditions of training, in case the results
are to be used as accurate measures of the rapidity of learning.

Examination of the detailed results of the white-black discrimination
tests as they appear in the tables of Chapter VII will reveal the fact
that some individuals succeeded in choosing correctly in a series of ten
tests after not more than five series, whereas others required at least
twice as many tests as the basis of a perfect series. In very few
instances, however, was a perfect habit of discrimination established by
fewer than one hundred tests. As the averages just presented in Table 41
indicate, fifteen series, or one hundred and fifty tests, were required
for the completion of the experiment. One might search a long time,
possibly, for another mammal whose curve of error in a simple
discrimination test would fall as gradually as that of the dancer. It is
fair to say that this animal learns very slowly as compared with most
mammals which have been carefully studied. It is to be remembered,
however, that quantitative results such as are here presented for the
dancer are available for few if any other animals except the white rat.
Neither in the form of the curve of learning nor in the behavior of the
animal as it makes its choice of an electric-box is there evidence of
anything which might be described as a sudden understanding of the
situation. The dancer apparently learns by rote. It exhibits neither
intelligent insight into an experimental situation nor ability to profit
by the experience of its companions. That the selection of the white box
occurs in various ways in different individuals, and even in the same
individual at different periods in the training process, is the only
indication of anything suggestive of implicit reasoning. Naturally enough
comparison of the two boxes is the first method of selection. It takes the
dancers a surprisingly long time to reach the point of making this
comparison as soon as they are confronted by the entrances to the two
electric-boxes. The habit of running from entrance to entrance repeatedly
before either is entered, once having been acquired, is retained often
throughout the training experiments. But in other cases, an individual
finally comes to the point of choosing by what appears to be the immediate
recognition of the right or the wrong box. In the former case the mouse
enters the white box immediately; in the latter, it rushes from the black
box into the white one without hesitation. So much evidence the
discrimination tests furnish of forms of behavior which in our fellow-men
we should interpret as rational.

[Illustration: FIGURE 31.--Curve of habit formation, plotted from the data
of labyrinth-D tests with ten males and ten females.]

Comparison of the error curves for the labyrinth tests (Figures 26 and 31)
with those for the discrimination tests (Figures 29 and 30) reveals
several interesting points of difference. The former fall very abruptly at
first, then with decreasing rapidity, to the base line; the latter, on the
contrary, fall gradually throughout their course. Evidently the labyrinth
habit is more readily acquired by the dancer than is the visual
discrimination habit. Certain motor tendencies can be established quickly,
it would seem, whereas others, and especially those which depend for their
guidance upon visual stimuli, are acquired with extreme slowness. From
this it might be inferred that the labyrinth method is naturally far
better suited to the nature of the dancer than is any form of the
discrimination method. I believe that this inference is correct, but at
the same time I am of the opinion that the discrimination method is of
even greater value than the labyrinth method as a means of discovering the
capacity of the animal for modification of behavior.

Inasmuch as my first purpose in the repetition of white-black
discrimination tests with a number of individuals was to obtain
quantitative results which should accurately indicate individual, age, and
sex differences in the rapidity of learning, it is important to consider
the reliability of the averages with which we have been dealing. Possibly
two groups of five male dancers each, chosen at random, would yield very
different results in discrimination tests. This would almost certainly be
true if the animals were selected from different lots, or were kept before
and during the tests under different environmental conditions. But from my
experiments it has become apparent that the average of the results given
by five individuals of the same sex, age, and condition of health, when
kept in the same environment and subjected to the same experimental tests,
is sufficiently constant from group to group to warrant its use as an
index of modifiability for the race. This expression, index of
modifiability, is a convenient mode of designating the average number of
tests necessary for the establishment of a perfect habit of white-black
discrimination. Hereafter I shall use it instead of a more lengthy
descriptive phrase.

As an indication of the degree of accuracy of measurements of the rapidity
of learning which are obtained by the use of 5 individuals I may offer the
following figures. For one of two directly comparable groups of 5 male
dancers which were chosen from 16 individuals which had been trained, the
number of tests which resulted in a perfect habit of white-black
discrimination was 92; for the other group it was 96. These indices for
strictly comparable groups of 5 individuals each differ from one another
by less than 5 per cent. Similarly, in the case of two groups of females,
the indices of modifiability were 94 and 104. These figures designate the
number of tests up to the point at which errors ceased for at least three
successive series (30 tests).

The determination of the probable error of the index of modifiability
further aids us in judging of the reliability of the measure of the
rapidity of learning which is obtained by averaging the results for 5
individuals. For a group of 5 males (Table 43, p. 243) the index was 72 +-
3.5; and for a group of 5 females of the same age as the males and
strictly comparable with respect to conditions of white-black training, it
was 104 +- 2.9. A probable error of +- 3.5 indicates the reliability of the
first of these indices of modifiability; one of +- 2.9, that of the second.

I do not doubt that 10 individuals would furnish a more reliable average
than 5, but I do doubt whether the purposes of my experiments would have
justified the great increase in work which the use of averages based upon
so large a group would have necessitated.

Further discussion of the index of modifiability may be postponed until
the several indices which serve as measures of the efficiency of different
methods of training have been presented in the next chapter.

From the data which constitute the materials of the present chapter it is
apparent that the results of the discrimination method are amenable to
much more accurate quantitative treatment than are those of the problem
method or the labyrinth method. But I have done little more as yet than
describe the method by which it is possible to measure certain dimensions
of the intelligence of the dancer, and to state some general results of
its application. In the remaining chapters it will be our task to discover
the value of this method and of the results which it has yielded.



The nature of the modifications which are wrought in the behavior of an
organism varies with the method of training. This fact is recognized by
human educators, as well as by students of animal behavior (makers of the
science of comparative pedagogy), but unfortunately accurate measurements
of the efficiency of our educational methods are rare.

Whatever the subject of investigation, there are two preeminently
important aspects of the educative process which may be taken as
indications of the value of the method of training by which it was
initiated and stimulated. I refer to the rapidity of the learning process
and its degree of permanency, or, in terms of habit formation, to the
rapidity with which a habit is acquired, and to its duration. Of these two
easily measurable aspects of the modifications in which training results,
I have chosen the first as a means to the special study of the efficiency
of the training to which the dancing mouse has been subjected in my

The reader who has followed my account of the behavior of the dancer up to
this point will recall that in practically all of the discrimination
experiments the number of tests in a series was ten. Some readers
doubtless have wondered why ten rather than five or twenty tests was
selected as the number in each continuous series. I shall now attempt to
answer the question. It was simply because the efficiency of that number
of tests, given daily, when taken in connection with the amount of time
which the conduct of the experiments required, rendered it the most
satisfactory number. But this statement demands elaboration and

Very early in my study of the dancer, I learned that a single experience
in a given experiment day after day had so little effect upon the animal
that a perfect habit could not be established short of several weeks or
months. Similarly, experiments in which two tests per day were given
proved that even a simple discrimination habit cannot be acquired by the
animal under this condition of training with sufficient rapidity to enable
the experimenter to study the formation of the habit advantageously. Next,
ten tests in succession each day were given. The results proved
satisfactory, consequently I proceeded to carry out my investigation on
the basis of a ten-test series. After this method had been thoroughly
tried, I decided to investigate the efficiency of other methods for the
purpose of instituting comparisons of efficiency and discovering the
number of tests per day whose efficiency, as measured by the rapidity of
the formation of a white-black discrimination habit, is highest.

For this purpose I carefully selected five pairs of dancers of the same
age, descent, and previous experience, and gave them white-black tests in
series of two tests per day (after the twentieth day the number was
increased to five) until they had acquired a perfect habit of
discriminating. Similarly other dancers were trained by means of series of
ten tests, twenty tests, or one hundred tests per day. Since it was my aim
to make the results of these various tests strictly comparable, I spared
no pains in selecting the individuals, and in maintaining constancy of
experimental conditions. The order of the changes in the position of the
cardboards which was adhered to in these efficiency tests was that given
in Table 12.

At the beginning of the two-test training I thought it possible that the
animals might acquire a perfect habit with only a few more days' training
than is required by the ten-test method. This did not prove to be the
case, for at the end of the twentieth day (after forty tests in all) the
average number of mistakes, as Table 42 shows, was 3.2 for the males and
3.0 for the females. Up to this time there had been clear evidence of the
formation of a habit of discriminating white from black, but, on the other
hand, the method had proved very unsatisfactory because the first test
each day usually appeared to be of very different value from the second.
On account of the imminent danger of the interruption of the experiment by
the rapid spread of an epidemic among my mice, I decided to increase the
number of tests in each series to five in order to complete the experiment
if possible before the disease could destroy the animals. On the twenty-
first day and thereafter, five-test series were given instead of two-test.
Unfortunately I was able to complete the experiment up to the point of
thirty successive correct tests with only six of the ten individuals whose
numbers appear at the top of Table 42. That the results of this table are
reliable, despite the fact that some of the individuals had to be taken
out of the experiment on account of bad condition, is indicated by the
fact that all the mice continued to do their best to discriminate so long
as they were used. Possibly the habit would have been acquired a little
more quickly by some of the individuals had they been stronger and more

It should be explained at this point that the results in all the
efficiency-of-training tables of this chapter are arranged, as in the
previous white-black discrimination tables, in tens, that is, each figure
in the tables indicates the number of errors in a series of ten tests. In
all cases _A_ and _B_ mark preliminary series of tests which were given at
the rate of ten tests per series. The numbers in the first column of these
tables designate groups of ten tests each, and not necessarily daily
series. In Table 42, for example, 1 includes the results of the first five
days of training, 2, of the next five days, and so on. The table shows
that No. 80 made seven wrong choices in the first five series of two tests
each. This method of grouping results serves to make the data for the
different methods directly comparable, and at the same time it saves space
at the sacrifice of very little valuable information concerning the nature
of the daily results. It is to be noted, with emphasis, that the two-five
tests per day training established a perfect habit after four weeks of
training. This method is therefore costly of the experimenter's time.



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