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The Dancing Mouse by Robert M. Yerkes

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SETS 80 82 84 86 88 AV. 73 79 83 85 89 AV.
OF 10

A 5 5 4 8 5 5.4 5 6 7 7 6 6.2
B 5 3 6 5 6 5.0 7 5 7 6 7 6.4

1 7 7 6 6 6 6.4 7 6 9 4 6 6.4
2 2 1 0 6 6 3.0 6 5 6 5 5 5.4
3 4 5 5 1 2 3.2 6 5 2 4 1 3.6
4 3 4 7 2 0 3.2 4 3 1 4 3 3.0
5 2 3 3 2 4 2.8 - 3 4 3 1 2.7
6 2 2 - 2 2 2.0 - 0 2 2 0 1.0
7 - 1 - 0 1 0.7 - 1 0 2 1 1.0
8 - - - 1 1 1.0 - 1 1 0 0 0.5
9 - - - 0 1 0.5 0 1 1 0 0 0.5
10 - - - 0 0 0 - 0 0 0 0 0
11 - - - 0 0 0 - 0 0 0
12 - - - 0 0 - 0 0 0



SETS 210 220 230 410 420 AV. 215 225 235 415 425 AV.
OF 10

A 6 5 6 6 6 5.8 8 4 4 8 5 5.8
B 6 8 8 5 1 5.6 8 7 6 6 2 5.8

1 6 7 6 2 4 5.0 7 6 5 6 4 5.6
2 4 3 1 2 3 2.6 5 6 4 2 5 4.4
3 3 1 4 3 4 3.0 3 3 4 2 5 4.4
4 5 0 3 3 2 3.2 2 1 3 3 3 2.4
5 3 0 4 1 4 2.4 1 3 3 3 3 2.6
6 2 1 4 0 1 1.6 2 1 1 1 0 1.0
7 1 0 3 1 0 1.0 1 1 2 3 3 2.0
8 0 0 1 0 0 0.2 0 0 2 2 3 2.0
9 0 0 0 1 0 0.2 1 0 0 1 1 0.6
10 0 0 0 0 0 2 1 0 2 1.0
11 0 0 0 0 3 0 1 0 0.8
12 0 0 0 0 0 2 0 0.4
13 0 0 0 0 0
14 0 0 0
15 0 0



SETS 72 74 208 240 402 AV. 217 230 245 403 407 AV.
OF 10

A 4 6 7 7 6 6.0 5 4 7 7 6 5.8
B 6 4 6 8 7 6.2 7 3 5 8 5 5.6

1 3 5 7 5 5 5.0 3 6 4 4 6 4.6
2 4 3 7 5 4 4.6 7 3 5 4 6 5.0
3 3 3 3 5 3 3.4 4 3 3 2 5 3.4
4 6 3 1 4 5 3.8 5 0 1 2 3 2.2
5 4 1 0 2 3 2.0 6 0 0 1 2 1.8
6 3 1 0 2 2 1.6 4 1 1 0 6 2.2
7 3 2 0 1 1 1.4 1 0 0 0 1 0.4
8 2 0 1 1 0.6 0 3 3 0 2 1.6
9 2 1 1 1 1.0 1 0 0 3 0.8
10 1 2 1 0 0.8 0 1 1 2 0.8
11 3 1 0 0 0.8 0 0 0 0 0
12 1 2 0 0 0.6 0 0 0 0 0
13 0 0 0 0 0 0 0 0
14 0 0 0
15 0 0 0

The results of the ten-test training as they appear in Table 43 need no
special comment, for quite similar data have already been examined in
other connections. In the case of this table it is to be remembered that
each figure represents the number of errors for a single day as well as
for a series of ten successive tests. The results of Table 44, on the
other hand, appear as subdivided series, since each daily series was
constituted by two series of ten tests, or in all twenty tests.

Finally, in Table 45 I have arranged the results of what may fairly be
called the continuous training method. In connection with several of the
labyrinth experiments of Chapter XIII continuous training proved very
satisfactory. It therefore seemed worth while to ascertain whether the
same method would not be more efficient than any other for the
establishment of a white-black discrimination habit. That this method was
not applied to ten individuals as were the two-five-test, the ten-test,
and the twenty-test methods is due to the fact that it proved practically
inadvisable to continue the tests long enough to complete the experiment.
I have usually designated the method as one hundred or more tests daily. I
applied this training method first to individuals Nos. 51 and 60. At the
end of one hundred and twenty tests with each of these individuals I was
forced to discontinue the experiment for the day because of the approach
of darkness. In the table the end of a series for the day is indicated by
a heavy line. The following day Nos. 51 and 60 succeeded in acquiring a
perfect habit after a few more tests.



SETS 51[1] 60 87 Av.
OF 10

A 5 5 6 5.3
B 5 3 7 5.0

1 6 6 5 5.7
2 3 2 5 3.3
3 5 4 7 5.3
4 7 4 5 5.3
5 6 2 3 3.7
6 1 1 3 1.7
7 4 2 3 3.0
8 3 3 0 2.0
9 2 2 3 2.3
10 5 0 2 2.3
11 1 2 2 1.7
12 2 1 1 1.3

13 4 1 2 2.3
14 1 2 1 1.3
15 3 1 5 3.0
16 3 3 2 2.7
17 1 0 1 0.7
18 2 0 1 1.0
19 0 0 2 0.7
20 0 0 0
21 0 1 0.3
22 -
23 -
24 -

[Footnote 1: Age of No. 51, 22 weeks. Age of No. 60, 17 weeks. Age of No.
87, 8 weeks.]

The results of the continuous training method for these two mice were so
strikingly different from those yielded by the other methods that I at
once suspected the influence of some factor other than that of the number
of tests per day. The ages of Nos. 51 and 60 at the time of their tests
were twenty-two and seventeen weeks, respectively, whereas all the
individuals used in connection with the other efficiency tests were four
weeks of age. It seemed possible that the slow habit formation exhibited
in the continuous training experiments might be due to the greater age of
the mice. I therefore selected a healthy active female which was only
eight weeks old, and tried to train her by the continuous training method.
With this individual, No. 87, the results were even more discouraging than
those previously obtained, for she was still imperfect in her
discrimination at the end of two hundred and ten tests. At that point the
experiment was interrupted, and it seemed scarcely worth while to continue
it further at a later date. The evidence of the extremely low efficiency
of the continuous method in comparison with the other methods which we
have been considering is so conclusive that further comment seems

We are now in a position to compare the results of the several methods of
training which have been applied to the dancer, and to attempt to get
satisfactory quantitative expressions of the efficiency of each method. I
have arranged in Table 46 the general averages yielded by the four
methods. Although these general results hide certain important facts which
will be exhibited later, they clearly indicate that an increase in the
number of tests per day does not necessarily result in an increase in the
rapidity of habit formation. Should we attempt, on superficial
examination, to interpret the figures of this table, we would doubtless
say that in efficiency the two-five-test method stands first, the
continuous-test method last, while the ten-test and twenty-test methods
occupy intermediate positions.



Number of Errors in White-Black Series for Different Methods of


A 5.8 5.8 5.9 5.3
B 5.7 5.7 5.9 5.0

1 6.4 5.3 4.8 5.7
2 4.2 3.5 4.8 3.3
3 3.4 3.2 3.4 5.3
4 3.1 2.5 3.0 5.3
5 2.7 2.5 1.9 3.7
6 1.5 1.3 1.9 1.7
7 0.9 1.5 0.9 3.0
8 0.7 0.8 1.1 2.0
9 0.5 0.4 0.9 2.3
10 0 0.5 0.8 2.3
11 0 0.4 0.4 1.7
12 0 0.2 0.3 1.3
13 0 0 2.3
14 0 0 1.3
15 0 0 3.0
16 2.7
17 0.7
18 1.0
19 0.7
20 0

We may now apply to the results of our efficiency-of-training tables the
method of measuring efficiency which was mentioned at the end of the
preceding chapter as the _index of modifiability (that number of tests
after which no errors occur for at least thirty tests)_. By taking the
average number of tests for the several individuals in each of the Tables
42, 43, 44, and 45 we obtain the following expressions of efficiency:--


Two-five-test 81.7 +- 2.7
Ten-test 88.0 +- 4.1
Twenty-test 91.0 +- 5.3
Continuous-test 170.0 +- 4.8

Since the difference between the indices for the ten-test and the twenty-
test methods lies within the limits of their probable errors (+-4.1 and
+-5.3) it is evident that it is not significant. Except for this, I think
these indices may be accepted as indications of real differences in the
value of the several methods of training.

A somewhat different interpretation of our results is suggested by the
grouping of individuals according to sex. In Table 47 appear the general
averages for the males and the females which were tested by the several
methods. The most striking fact exhibited by this table is that of the
high efficiency of the twenty-test method for the females. Apparently they
profited much more quickly by this method than by the ten-test method,
whereas just the reverse is true of the males. I present the data of this
table merely to show that general averages may hide important facts.



2 or 5 tests per day 85.0 80.0
10 tests per day 72.0 104.0
20 tests per day 94.0 88.0
100 or more tests per day 160.0 180.0

From all considerations that have been mentioned thus far the reader would
be justified in concluding that I made a mistake in selecting the ten-test
method for my study of the modifiability of the behavior of the dancer.
That this conclusion is not correct is due to the time factor in the
experiments. If the dancer could acquire a perfect habit as a result of
twelve days' training, no matter whether two, five, ten, or twenty tests
were given daily, it would, of course, be economical of time for the
experimenter to employ the two-test method. But if, on the contrary, the
two-test method required twice as many days' training as the five-test
method, it would be economical for him to use the five-test method despite
the fact that he would have to give a larger number of tests than the two-
test method would have demanded. In a word, the time which the work
requires depends upon the number of series which have to be given, as well
as upon the number of tests in each series. As it happens, the ten-test
method demands less of the experimenter's time than do methods with fewer
tests per day. The twenty-test method is even more economical of time, but
it has a fatal defect. It is at times too tiresome for both mouse and man.
These facts indicate that a balance should be struck between number of
tests and number of series. The fewer the tests per day, within the limits
of two and one hundred, the higher the efficiency of the method of
training, as measured in terms of the total number of tests necessary for
the establishment of a perfect habit, and the lower its efficiency as
measured in terms of the number of series given. The greater the number of
tests per day, on the other hand, the higher the efficiency of the method
in terms of the number of series, and the lower its efficiency in terms of
the total number of tests. By taking into account these facts, together
with the fact of fatigue, we are led to the conclusion that ten tests per
day is the most satisfactory number.

If my time and attention had not been fully occupied with other problems,
I should have determined the efficiency of various methods of training in
terms of the duration of habit, as well as in terms of the rapidity of its
formation. As these two measures of efficiency might give contradictory
results, it is obvious that a training method cannot be fairly evaluated
without consideration of both the rapidity of habit formation and the
permanency of the habit. A _priori_ it seems not improbable that slowness
of learning should be directly correlated with a high degree of
permanency. By the further application of the method which I have used in
this study of the efficiency of training we may hope to get a definite
answer to this and many other questions concerning the nature of the
educative process and the conditions which influence it.



The effects of training gradually disappear. Habits wane with disuse. In
the dancer, it is not possible to establish with certainty the existence
of memory in the introspective psychological sense; but it is possible to
measure the efficiency of the training to which the animal is subjected,
and the degree of permanency of habits. The materials which constitute
this chapter concern the persistence of unused habits, and the influence
of previous training on the re-acquisition of a habit which has been lost
or on the acquisition of a new habit. For convenience of description, I
shall refer to certain of the facts which are to be discussed as facts of
memory, with the clear understanding that consciousness is not necessarily
implied. By memory, wherever it occurs in this book, I mean the ability of
the dancer to retain the power of adaptive action which it has acquired
through training.

I first discovered memory in the dancer, although there was previously no
reason for doubting its existence, in connection with the ladder-climbing
tests of Chapter XII. In this experiment two individuals which had
perfectly learned to escape from the experiment box to the nest-box by way
of the wire ladder, when tested after an interval of two weeks, during
which they had remained in the nest-box without opportunity to exercise
their newly acquired habit, demonstrated their memory of the method of
escape by returning to the nest-box by way of the ladder as soon as they
were given opportunity to do so. As it did not lend itself readily to
quantitative study, no attempts were made to measure the duration of this
particular habit. At best the climbing of a wire ladder is of very
uncertain value as an indication of the influence of training.

Similarly, the persistence of habits has been forced upon my attention day
after day in my various experiments with the mice. It is obvious, then,
that the simple fact of memory is well established, and that we may turn
at once to an examination of the facts revealed by special memory and re-
learning experiments.

The visual discrimination method, which proved invaluable as a means of
measuring the rapidity of habit formation, proved equally serviceable in
the measurement of the permanency or duration of habits. Memory tests for
discrimination habits were made as follows. After a dancer had been
trained in the discrimination box so that it could choose the correct
electric-box, white, red, blue, or green as it might be, in three
successive daily series of ten tests each, it was permitted to remain for
a certain length of time without training and without opportunity to
exercise its habit of visual discrimination and choice. At the expiration
of the rest interval, as we may designate the period during which the
habit was not in use, the mouse was placed in the discrimination box under
precisely the same conditions in which it had been trained and was given a
series of ten memory tests with the box to be chosen alternately on the
right and on the left. In order that the entire series of ten tests, and
sometimes two such series given on consecutive days, might be available as
indications of the duration of a habit, the mouse was permitted to enter
and pass through either of the electric-boxes without receiving a shock.
Had the shock been given as punishment for a wrong choice, it is obvious
that only the first test of the memory series would be of value as an
indication of the existence of a previously acquired habit. Even under the
conditions of no shock and no stop or hindrance the first test of each
memory series is of preeminent importance, for the mouse tends to persist
in choosing either the side or the visual condition (sometimes one,
sometimes the other) which it chooses in the first test. If the wrong box
is chosen to begin with, mistakes are likely to continue because of the
lack of punishment; in this case the animal discriminates, but there is no
evidence that it remembers the right box. Likewise, if the right electric-
box is chosen in the first test, correct choices may continue simply
because the animal has discovered that it can safely enter that particular
box; again, the animal discriminates without depending necessarily upon
its earlier experience. I have occasionally observed a series of ten
correct choices, made on the basis of an accidental right start, followed
by another series in which almost every choice was wrong, because the
animal happened to start wrong.

As the results of my tests of memory are of such a nature that they cannot
advantageously be averaged, I have arranged in Table 48 a number of
typical measurements of the duration of visual discrimination habits. In
this table I have indicated the number and age of the individual tested,
the habit of discrimination which had been acquired, the length of the
rest interval, the result of the first test (right or wrong), and the
number of errors made in each series of ten memory tests.





1000 25 weeks White-black 4 weeks Right 0
5 27 White-black 4 Right 5 7
210 15 White-black 8 Right 5
220 15 White-black 8 Right 4
230 15 White-black 8 Wrong 5
215 15 White-black 8 Right 5
225 15 White-black 8 Right 2
235 15 White-black 8 Right 7
410 15 White-black 8 Wrong 4
415 15 White-black 8 Wrong 6
420 15 White-black 8 Wrong 3
425 15 White-black 8 Right 3
2 28 Black-white 4 Wrong 9
7 17 Black-white 2 Wrong 1
7 21 Black-white 6 Right 1
7 27 Black-white 10 Right 1 6
998 18 Black-white 2 Wrong 3
998 22 Black-white 4 Right 0
998 28 Black-white 10 Right 5 5
13 10 Black-white 4 Right 3
14 10 Black-white 4 Right 3
15 10 Black-white 4 Right 2
16 10 Black-white 4 Right 4
1000 25 Light blue-orange 4 Right 4
2 28 Light blue-orange 2 Wrong 5
5 28 Light blue-orange 6 Wrong 4 6
3 25 Light blue-orange 4 Wrong 8
10 24 Light blue-orange 2 Right 8
10 26 Light blue-orange 2 Right 5
11 25 Light blue-orange 2 Right 6
11 27 Light blue-orange 2 Wrong 5
151 13 Green-red 2 Right 1 0
152 13 Green-red 2 Right 5 1

This quantitative study of the duration of simple habits of choice showed
that in the majority of cases a perfectly acquired habit persists for at
least two weeks. To be perfectly fair to the animal I must restrict this
statement to visual conditions other than colors, for the dancer exhibited
little ability either to acquire or to retain a habit of distinguishing
spectral colors. Altogether, I made a large number of white-black and
black-white memory tests after rest intervals of four, six, eight, or ten
weeks. The results for the four-week interval show extreme individual
differences in memory. Number 1000, for example, was able to choose
correctly every time in a series of white-black tests after a rest
interval of four weeks, whereas No. 5 was wrong as often as she was right
after the same interval. I have placed the results for these two
individuals at the head of the table because they suggest the variations
which render averages undesirable. Number 1000 had a perfect habit at the
end of four weeks of disuse; No. 5 had no habit whatever. I shall reserve
further discussion of age, sex, and individual differences in the
permanency of habits for the next chapter.

With Nos. 7 and 998 memory tests were made after three different rest
intervals. At the end of two weeks the black-white habit was present in
both individuals, although it was not perfect. After six and four weeks,
respectively (see Table 48), it still persisted; in fact, it apparently
had improved as the result of additional training after the earlier memory
tests. At the expiration of ten weeks it had wholly disappeared. In her
first series of memory tests after the ten-week interval No. 7 made only
one error, but a chance choice of the black (right) in the first test and
the subsequent choice of the box in which no shock had been received serve
to account for results which at first appear to be indicative of memory.
That this explanation is correct is proved by the fact that a second
memory series, in which the first choice happened to be wrong, resulted in
six mistakes. Evidently she had lost the habit.

In no instance have memory tests definitely indicated the presence of a
habit after a rest interval of more than eight weeks. It is safe,
therefore, to conclude from the results which have been obtained that a
white-black or black-white discrimination habit may persist during an
interval of from two to eight weeks of disuse, but that such a habit is
seldom perfect after more than four weeks.

The measurements of memory which were made in connection with color
discrimination experiments are markedly different from those which were
obtained in the brightness tests. As might have been anticipated (?), in
view of the extreme difficulty with which the dancer learns to
discriminate colors, the habit of discriminating between qualitatively
different visual conditions does not persist very long. I have never
obtained evidence of a perfect habit after an interval of more than two
weeks, and usually, as is apparent from Table 48, the tests indicated very
imperfect memory at the end of that interval. It seems probable that even
in these so-called color tests discrimination is partly by brightness
difference, and that the imperfection of the habit and its short duration
are due to the fact that the basis of discrimination is inadequate. This
is the only explanation which I have to offer for the difference which has
been demonstrated to exist between the duration of brightness
discrimination habits and color discrimination habits.

The duration of a discrimination habit having been measured with a fair
degree of accuracy, I undertook the task of ascertaining whether training
whose results have wholly disappeared, so far as memory tests are in
question, influences the re-acquisition of the same habit. Can a habit be
re-acquired with greater facility than it was originally acquired? Is re-
learning easier than learning? To obtain an answer to the question which
may be asked in these different forms, ten individuals were experimented
with in accordance with a method whose chief features are now to be
stated. In each of these ten individuals a perfect white-black habit was
established by the use of the standard series of tests the order of which
is given in Table 12. At the expiration of a rest interval of eight weeks
precisely the same series of tests were repeated as memory and re-training
tests. In this repetition, the preliminary series, _A_ and _B_, served as
memory tests, and the subsequent training series, as re-training series.

[Illustration: FIGURE 32.--Error curves plotted from the data given by ten
dancers in white-black discrimination tests. The solid line ([Symbol:
solid line]) is the error curve of the original learning process; the
broken line (------) is that of the re-learning process, after an interval
of eight weeks.]

The striking results of this investigation of re-learning are exhibited in
the curves of learning and re-learning of Figure 32. These curves make it
appear that the mice re-acquired the white-black discrimination habit much
more readily than they had originally acquired it. But in addition to
furnishing the basis for some such statement as the foregoing, the curves
suggest a serious criticism of the experiment.

In the original tests, the preliminary series indicated a strong
preference for black. In series _A_ it was chosen on the average 5.8 times
in 10, and in series _B_, 5.7 times. This preference was rapidly overcome
by the training series, and at the end of 130 tests discrimination was
perfect. All this appears in the curve of learning (solid line of figure).
On the other hand, these preliminary series when repeated as memory tests,
after a rest-interval of eight weeks, gave markedly different results.
Series _A_ indicated preference for white (5.6 times in 10) instead of
black, and series _B_ indicated only a slight preference for black. In
brief, series _A_ and _B_ show that the preference for black was
considerably stronger at the beginning of the training than at the
beginning of the re-training.

In the light of these facts it is fair to claim that the effects of the
white-black training had not wholly disappeared as the result of eight
weeks of rest, and that the experiment therefore fails to furnish
satisfactory grounds for the statement that re-learning occurs more
rapidly than learning. I accept this criticism as pertinent, although not
necessarily valid, and at the same time I freely admit that the results
have a significance which I had not anticipated. But they are not less
interesting or valuable on that account. Granting, then, that at least
some of the ten individuals which took part in the experiment had not
completely lost the memory of their white-black training at the end of
eight weeks, it is still possible that an examination of the individual
results may justify some conclusion concerning the question which was
proposed at the outset of the investigation. Such an examination is made
possible by Tables 49 and 50, in which I have arranged separately the
results for the males and the females.



210 220 230 410 420 AV. 210 220 230 410 420 AV.

A 6 5 6 6 6 5.8 5 4 5 4 3 4.2
B 6 8 8 5 1 5.6 8 4 5 4 6 5.4

1 6 7 6 2 4 5.0 3 3 4 7 3 4.0
2 4 3 1 2 3 2.6 2 4 2 5 3 3.2
3 3 1 4 3 4 3.0 1 4 1 4 1 2.2
4 5 0 3 3 2 2.6 0 1 0 1 2 0.8
5 3 0 4 1 4 2.4 0 2 0 2 0 0.8
6 2 1 4 0 1 1.6 0 1 0 0 2 0.6
7 1 0 3 1 0 1.0 0 0 0 0
8 0 0 1 0 0 0.2 0 0 1 0.2
9 0 0 0 1 0 0.2 0 0 0
10 0 0 0 0 1 0.2
11 0 0 0 0 0
12 0 0 0 0
13 0 0

Only three of the ten individuals failed to re-acquire the habit of white-
black discrimination more quickly than it had originally been acquired,
and, in the case of these exceptions, No. 220 required exactly the same
number of tests in each case, and No. 420 was placed at a slight
disadvantage in the re-learning series by an interruption of the training
between the seventh and the eighth series. Had his training been completed
by the sixth series he too would have had the same number of tests in
training and re-training. Moreover, and this is of preeminent importance
for a fair interpretation of the results, in several instances even those
individuals which exhibited as strong a preference for the black in the
memory series as in the preliminary series re-learned more quickly than
they had learned. Number 210, for example, although he gave no evidence of
memory, and, in fact, chose the black more frequently in the memory series
than he did in the preliminary series, re-acquired the discrimination
habit in less than half the number of tests which had been necessary for
the establishment of the habit originally.




215 225 235 415 425 Av. 215 225 235 415 425 Av.
A 8 4 4 8 5 5.8 5 2 7 6 3 4.6
B 8 7 6 6 2 5.8 8 5 6 4 3 5.2
1 7 6 5 6 4 5.6 4 1 5 4 3 3.4
2 5 6 4 2 5 4.4 1 1 1 2 3 1.6
3 3 3 4 3 4 3.4 1 0 3 6 0 2.0
4 2 1 3 3 3 2.4 0 0 3 3 1 1.4
5 1 3 3 3 3 2.6 0 0 died 2 0 0.5
6 2 1 1 1 0 1.0 0 1 0 0.2
7 1 1 2 3 3 2.0 0 0 0
8 0 0 2 2 3 1.4 1 0.2
9 1 0 0 1 1 0.6 0 0
10 0 2 1 0 2 1.0 0 0
11 0 3 0 1 0 0.8 0 0
12 0 0 0 2 0 0.4
13 0 0 0 0 0
14 0 0 0
15 0 0

The facts which have been presented thus far become more significant when
the indices of modifiability for the learning and the re-learning
processes are compared.



Females . . . . . . . 104 42.5
Males . . . . . . . . 72 54

The behavior of the mice in the experiments, the detailed results of
Tables 49 and 50, and the indices of modifiability together justify the
following conclusions. Most of the ten dancers, at the end of a rest
interval of eight weeks, had so far lost the habit of white-black
discrimination that memory tests furnished no conclusive evidence of the
influence of previous training; a few individuals seemed to possess traces
of the habit after such an interval. In the case of each group of
individuals re-training brought about the establishment of a perfect habit
far more quickly than did the original training. This suggests the
existence of two kinds or aspects of organic modification in connection
with training; those which constitute the basis of a definite form of
motor activity, and those which constitute the bases or dispositions for
the acquirement of certain types of behavior. There are several
indications that further study of the modifiability of behavior will
furnish the facts which are necessary to render this suggestion

Closely related to the facts which have been revealed by the re-training
experiments are certain results of the labyrinth experiments. For the
student of animal behavior, as for the human educator, it is of importance
to learn whether one kind of training increases the efficiency of similar
forms of training. Can a dancer learn a given labyrinth path the more
readily because it has previously had experience in another form of

The answer to this question, which my experimental results furnish, is
given in Table 51. In the upper half of the table have been arranged the
results for six individuals which were trained first in labyrinth B, then
in labyrinth C, and finally in labyrinth D. Below, in similar fashion, are
given the results for six individuals which were trained in the same three
labyrinths in the order C, B, D, instead of B, C, D. My purpose in giving
the training in these two orders was to ascertain whether labyrinth C,
which had proved to be rather difficult for most individuals, would be
more easily learned if the training in it were preceded by training in
labyrinth C.



76 8 14 3 19 4 7
78 5 20 6 14 4 5
86 13 22 5 12 3 9
75 4 15 8 19 4 13
77 7 11 11 29 11 12
87 12 22 9 20 4 9

AV. 8.2 17.3 7.0 18.8 5.0 9.2


58 16 -- 2 14 7 10
60 17 -- 13 37 10 14
88 25 35 9 22 4 8
49 34 -- 1 5 7 8
57 15 -- 3 20 3 6
85 11 18 2 11 3 4

AV. 19.7 26.5 5.0 18.2 5.7 8.3

The results are sufficiently definite to warrant the conclusion that
experience in B rendered the learning of C easier than it would have been
had there been no previous labyrinth training. Those individuals whose
first labyrinth training was in C made their first correct trip as the
result of 19.7 trials, whereas those which had previously been trained in
labyrinth B were able to make a correct trip as the result of only 7.0
trials. Similarly the table shows that training in C rendered the
subsequent learning of B easier. To master B when it was the first
labyrinth required 8.2 trials; to master it after C had been learned
required only 5 trials. In addition to proving that the acquisition of one
form of labyrinth habit may facilitate the acquisition of others,
comparison of the averages of Table 51 furnishes evidence of the truth of
the statement that no results of training can be properly interpreted in
the absence of knowledge of the previous experience of the organism.



All dancers are alike in certain important respects, but to the trained
observer of animal behavior their individual peculiarities are quite as
evident, and even more interesting than their points of resemblance.
Omitting consideration of the structural marks of individuality, we shall
examine the individual, age, and sex differences in general behavior,
rapidity of learning, memory, and discrimination, which have been revealed
by my experiments. Observations which bear on the subject of differences
are scattered through the preceding chapters, but in no case have they
been given sufficient prominence to force them upon the attention of those
who are not especially interested in individual peculiarities. It has
seemed worth while, therefore, to assemble all the available material in
this chapter for systematic examination and interpretation.

In the pages which follow, individual, age, and sex peculiarities are
discussed in turn. Within each of these three groups of differences I have
arranged in order what Royce has appropriately named the facts of
discriminating sensitiveness, docility, and initiative. Individuals of the
same age and sex no less than those which differ in sex or age exhibit
important differences in ability to discriminate among sense impressions
("discriminative sensitiveness"), in ability to profit by experience
("docility"), and in ability to try new kinds of behavior ("initiative").

Individual differences in sensitiveness to visual, auditory, tactual, and
olfactory stimuli have been revealed by many of my experiments. The
brightness discrimination tests conclusively proved that a degree of
difference in illumination which is easily detectable by one dancer may be
beyond the discriminating sensitiveness of another. Both the tests with
gray papers and those with the Weber's law apparatus furnished striking
evidence of individual differences in the kind of visual sensitiveness
which throughout this book has been called brightness vision. I suspect
that certain of the differences which were observed should be referred to
the experience of the individuals rather than to the capacity of the
visual organs, for training improves visual discrimination to a much
greater extent than would ordinarily be thought possible. To the truth of
this statement the results of the Weber's law experiments with No. 51 bear
witness. Likewise in color discrimination there are individual
differences, examples of which may be discovered by the examination of the
results given in Chapters IX and X.

No differences in auditory sensitiveness appeared in my adult dancers, for
in none of them was there definite response to sounds, but among the young
individuals differences were prominent. I may call attention to the data
on this subject which Table 5, p. 89, contains. The mice in four out of
twelve litters gave no indications of hearing any sounds that I was able
to produce; the remaining individuals responded with varying degrees of
sensitiveness. I made no attempt to measure this sensitiveness, but it
obviously differed from mouse to mouse. I feel justified, therefore, in
stating that the young dancers exhibit extreme individual difference in
sensitiveness to sounds.

My observations of differences in sensitiveness to other forms of
stimulation were made in connection with training tests, and although they
are not quantitative, I venture to call attention to them. Indeed, I am
led by the results of my study of various aspects of the dancer's behavior
to conclude that the race exhibits individual differences in
discriminating sensitiveness to a far greater extent than do most mammals,
not excepting man. The importance of this fact (for I am confident that
any one who carefully examines the detailed results of the various
experiments which are described in this book will agree that it is an
established fact) cannot be overlooked. It alters our interpretation of
the results of training, memory, heredity, and discrimination experiments,
and it leads us to suspect that the dancing race is exceedingly unstable.
I do not venture to make comparison of my own observations of the dancer's
sense equipment with those of Cyon, Rawitz, Zoth, and Kishi, for the
differences are too great in many instances to be thought of as other than
species or variety peculiarities. It has seemed fairer to compare only
individuals of the same breed, or, as I have done and shall continue to do
throughout this chapter, of two lines of descent.

With respect to docility individual differences are prominent. We need
only turn to the various tables of results to discover that in
modifiability of behavior, in memory, in re-learning, not to mention other
aspects of docility, dancers of the same sex and age differed strikingly.
Let me by way of illustration cite a few cases of difference in docility.
Number 1000 learned to discriminate white from black more quickly and
retained his habit longer than any other dancer with which I have
experimented. I should characterize him as an exceptionally docile
individual. Table 44 offers several examples. Numbers 403 and 407, though
they were born in the same litter and were alike in appearance and in
conditions of life, acquired the white-black habit with a difference in
rapidity which is expressed by the indices of modifiability 50 and 100. In
other words, it took No. 407 twice as long to acquire this habit as it
took No. 403. Similarly the ladder-climbing tests revealed important
individual differences in ability to profit by experience. In the tables
of labyrinth tests (38, 39, 40) individual differences are too numerous to
mention. It required forty-nine tests to establish in No. 50 a labyrinth-C
habit which was approximately equal in degree of perfection to that which
resulted from twenty-two tests in the case of No. 52. The figures in this
and other instances do not exaggerate the facts, for repeatedly I have
tested individuals of the same litter, the same sex, and, so far as I
could judge, of the same stage of development, and obtained results which
differ as markedly as do those just cited. If space limits permitted, I
could present scores of similar differences in docility which the problem,
labyrinth, and discrimination methods have revealed.

In examining the detailed individual results of the various tables for
differences of this sort, it is important to bear in mind that sex, age,
and descent should be taken into account, for with each of them, as will
be shown clearly later in this chapter, sensitiveness, docility, and
initiative vary. I have therefore based my statements concerning
individual differences in docility upon the results of comparison of mice
of the same litter, sex, and age. It is safe to say that human beings
similarly selected for comparison do not exhibit greater differences in
ability to profit by experience than did these dancing mice.

The facts concerning individual differences in initiative which I have
discovered are not less definite than those of the preceding paragraphs.
From the beginning of my study of the dancer I observed that what one
individual would readily learn of his own initiative another never
learned. For example, in the ladder-climbing experiment No. 1000
distinguished himself for his initiative, whereas Nos. 4 and 5 never
acquired the habit of escaping from confinement by using the ladder. I
noticed, in this test of the animal's ability to learn, that while one
individual would be scurrying about trying all ways of escape,
investigating its surroundings, looking, sniffing, and dancing by turns,
another would devote all its time to whirling, circling, or washing
itself. One in the course of its activity would happen upon the way of
escape, the other by reason of the limited scope of its activity, not the
lack of it, would fail hour after hour to discover even the simplest way
of getting back to its nest, to food, and to its companions. Hundreds of
times during the past three years I have noticed important individual
differences in initiative in connection with the discrimination
experiments. The swinging wire doors which one dancer learned to push open
before he had been in the box five minutes, another might not become
familiar with through his own initiative for hours or days. In fact, it
was not seldom that I had to teach an individual to pass from one
compartment to the other by gently pushing him against the door until it
opened sufficiently to allow him to squeeze through. Occasionally a mouse
learned to pull the doors open so that he could pass through the openings
in either direction with facility. This was a form of individual
initiative which I had not anticipated and did not especially desire, so I
did not encourage its development, but, nevertheless, at least one fourth
of the mice which I experimented with in the discrimination box learned
the trick. The other three fourths, although they were used in the box day
after day sometimes for weeks, never discovered that they might return to
the nest-box by pulling the swing-door through which they had just passed
as well as by entering one of the electric-boxes.

Another indication of individual initiative in action appeared in the
tendency of certain mice to climb out of the experiment boxes or
labyrinths. It would have been extremely easy for any of the mice to
escape from the labyrinths by scaling the walls of the alleys, for they
were only 10 cm. in height, and when a dancer stood on its hind legs it
could easily reach the top with its nose. But, strange though it will seem
to any one who has not worked with the dancer, not more than one in ten of
the animals which I observed made any attempt to escape in this manner.
They lacked initiative. That it was not due to a lack of the power to
climb, I abundantly demonstrated by teaching a few individuals that a
scramble in one corner meant easy escape from the maze of paths. I do not
think any one of the mice was physically incapable of climbing, but I am
confident that they differed markedly, not only in the willingness to try
new modes of action, but in the readiness with which they could climb. I
have already said that individuals differ noticeably in the scope of their
activity. By this statement I mean that they try a varying number of kinds
of activity. As in the case of men, so in mice, one individual will do a
greater number of things in a few hours than another will in weeks or
months. The dancers differ in versatility, in individual initiative, as do
we, albeit not so markedly.

Important differences which may with certainty be described as age
differences are not so obvious as are such marks of individuality as have
been set forth in the preceding pages. I have noted few changes in
discriminative sensitiveness, other than those with regard to auditory
sensitiveness, which could be correlated with age. In certain instances
adults appeared to be able to discriminate more accurately and more easily
than young mice, but it is difficult to say whether this change belongs
under sensitiveness or docility. I have not made an ontogenetic study of
the senses, and I am therefore unable to describe in detail the course of
their development and decline. Of one important fact I am certain, that
discriminative sensitiveness increases up to a certain point with age and
with training.

Differences in docility which are obviously to be correlated with age
abound. In the prime of its life (from the second to the tenth month) the
dancer is active, full of energy, quick to learn; in its senility (during
the second year) it is inactive, but at times even more docile than during
the period of greatest physical development. Frequently I have noticed in
connection with labyrinth tests that individuals of the age of a year or
more learn much more quickly than do individuals of the age of two or
three months. But, on the other hand, I have contradictory observations,
for now and then I obtained just the opposite result in experiments to
test docility. Evidently this is a matter which demands systematic,
quantitative investigation. Casual observation may suggest conclusions,
but it will not justify them.

Early in my investigation of the behavior of the dancer I conceived the
idea of determining the relation of modifiability of behavior (docility)
to age. The question which was foremost in my mind and for which I first
sought an answer may be stated thus: can the dancer acquire a given habit
with the same facility at different ages? Since the visual discrimination
experiment seemed to be well suited for the investigation of this problem
I planned to train, in the white-black discrimination experiment, five
pairs of dancers at the age of one month, and the same number for each of
the ages four, seven, ten, thirteen, sixteen, and nineteen months.[1]

[Footnote 1: I have not been able thus far to determine the average length
of the dancer's life. The greatest age to which any of my individuals has
attained is nineteen months.]

To test the same individuals month after month would be the ideal way of
obtaining an answer to our question, but I could devise no satisfactory
way of doing this. The effects of training last so long, as the results of
the previous chapter proved, and the uncertainty of their entire
disappearance is so serious, that the same training process cannot be used
at successive ages. The use of different methods of training is even more
unsatisfactory because it is extremely difficult to make accurate
quantitative comparison of their results. It was these considerations that
forced me to attempt to discover the relation of docility to age by
carrying out the same experiments with groups of individuals of different

As my plan involved the execution of precisely the same set of tests with
at least seventy individuals whose age, history, and past experience were
accurately known, and of which some had to be kept for nineteen months
before they could be trained, the amount of labor and the risk of mishap
which it entailed were great. To make possible the completion of the
investigation within two years, I accumulated healthy individuals for
several months without training any of them. In March, 1907, I had
succeeded in completing the tests for the age of one month, and I had on
hand for the remaining tests almost a hundred individuals, whose ages
ranged from a few days to eighteen months. Had everything gone well, the
work would have been finished within six months. Suddenly, and without
discoverable external cause, my mice began to die of an intestinal
trouble, and despite all my efforts to check the disease by changing food
supply and environment, all except a single pair died within a few weeks.
Thus ended a number of experiments whose final results I had expected to
be able to present in this volume. However, the work which I have done is
still of value, for the single pair of survivors have made possible the
continuance of my tests with other individuals of the same line of descent
as those which perished, and I have to regret only the loss of time and

As I have on hand results for ten individuals of the age of one month, and
for four individuals of the age of four months, it has seemed desirable to
state the problem, method, and incomplete results of this study of the
relation of modifiability to age. The indices of modifiability for these
two groups of dancers differ so strikingly that I feel justified in
persisting in my efforts to obtain comparable data for the seven ages
which have been mentioned.



Number of Errors in Successive Daily Series of Ten White-Black
Tests, with Dancers Four Months Old


NO. 76 NO. 78 AV. NO. 75 NO. 77 AV. GENERAL AV.

A 7 7 7.0 4 8 6.0 6.50
B 8 6 7.0 6 5 5.5 6.25

1 5 5 5.0 5 5 5.0 5.00
2 5 4 4.5 2 2 2.0 3.25
3 4 5 4.5 2 5 3.5 4.00
4 3 4 3.5 1 1 1.0 2.25
5 5 2 3.5 0 1 0.5 2.00
6 3 2 2.5 1 0 0.5 1.50
7 2 1 1.5 1 2 1.5 1.50
8 5 1 3.0 0 0 0 1.50
9 1 3 2.0 0 0 0 1.00
10 1 2 1.5 1 0 0.5 1.00
11 1 1 1.0 0 0 0.50
12 1 1 1.0 0 0 0.50
13 0 0 0 0 0 0
14 0 0 0 0
15 0 0 0 0

[Illustration: FIGURE 33.--Plasticity curves. In the left margin are given
the indices of modifiability (the number of tests necessary for the
establishment of a perfect habit). Below the base line the age of the
individuals is given in months. Curve for males, --------; curve for
females, - - - -; curve for both males and females,----. When these three
plasticity curves are completed, they will represent the indices of
modifiability as determined for ten individuals at the age of 1 month, and
similarly for the same number of individuals at each of the ages, 4, 7,
10, 13, 16, and 19 months.]

The detailed results for the one-month old individuals appear in Table 43;
those for the four-month individuals in Table 52. The general averages for
the former are to be found in the third column of Table 46, under the
heading "10 tests per day"; those for the latter in the last column of
Table 52. Mere inspection of these tables reveals the curious sex
difference which goes far towards justifying the presentation of this
uncompleted work. The index of modifiability for the ten one-month
individuals is 88 (that is, 88 tests were necessary for the establishment
of a habit); for the four-month individuals it is 102.5. The heavy solid
line of Figure 33 joins the points on the ordinates at which these values
are located. Apparently, then, the dancer acquires the white-black
discrimination habit less readily at the age of four months than at the
age of one month.

Further analysis of the results proves that this statement is not true.
When the averages for the two sexes are compared, it appears that the
males learned much less quickly at four months than at one month, whereas
just the reverse is true of the females. The dash and dot line of the
figure extends from the index of modifiability of the one-month males (72)
to that of the four-month males (120); and the regularly interrupted line
similarly joins the indices of the one-month (104) and the four-month (85)
females. In seeking to discover age differences in docility or ability to
profit by experience we have stumbled upon what appears to be an important
sex difference. Perhaps I should add to this presentation of partial
results the following statement. Since there are only four individuals in
the four-month group, two of each sex, the indices are not very reliable,
and consequently too much stress should not be laid upon the age and sex
differences which are indicated.

In view of this impressive instance of the way in which averages may
conceal facts and lead the observer to false inferences, I wish to remark
that my study of the dancer has convinced me of the profound truth of the
statement that the biologist, whether he be psychologist, anthropologist,
physiologist, or morphologist, should work with the organic individual and
should first of all deal with his results as individual results. Averages
have their place and value, but to mass data before their individual
significance has been carefully sought out is to conceal or distort their
meaning. Too many of us, in our eagerness for quantitative results and in
our desire to obtain averages which shall justify general statements, get
the cart before the horse.

Figure 33 presents the beginning of what I propose to call plasticity
curves. When these three curves are completed on the basis of experiments
with five dancers of each sex for each of the ages indicated on the base
line of the figure, they will indicate what general changes in plasticity,
modifiability of behavior, or ability to learn (for all of these
expressions have been used to designate much the same capacity of the
organism) occur from the first month to the nineteenth in the male and the
female dancer, and in the race without respect to sex. So far as I know,
data for the construction of plasticity curves such as I hope in the near
future to be able to present for the dancing mouse have not been obtained
for any mammal.

At present it would be hazardous for me to attempt to state any general
conclusion concerning the relation of docility to age.

The initiative of the dancer certainly varies with its age. In scope the
action system rapidly increases during the first few months of life, and
if the animal be subjected to training tests, this increase may continue
well into old age. The appearance of noticeable quiescence does not
necessarily indicate diminished initiative. Frequently my oldest mice have
shown themselves preeminent in their ability to adjust their behavior to
new conditions. However, I have not studied individuals of more than
eighteen months in age. One would naturally expect initiative to decrease
in senility. All that I can say is that I have seen no indications of it.

We may now briefly consider the principal sex differences which have been
revealed by the experiments. In sensitiveness I have discovered no
difference, but it should be stated that no special attention has been
given to the matter. In docility the males usually appeared to be superior
to the females. This was especially noticeable early in my visual
discrimination tests. The males almost invariably acquired a perfect habit
quicker than the females. I may cite the following typical instances.
Number 14 acquired the black-white habit with 40 tests; No. 13, with 60
(Table 10, p. 109). Of the five pairs of individuals whose records in
white-black training appear in Table 43, not one contradicts the statement
which has just been made. It is to be noted, however, that under certain
conditions of training, for example, 20 tests per day, the female is at an
advantage. Recently I have with increasing frequency obtained measures of
docility which apparently favor the female. That this difference in the
results is due to a difference in age is probable.

In labyrinth tests the female is as much superior to the male as the male
is to the female in discrimination tests. From the tables of Chapter XIII
I may take a few averages to indicate the quantitative nature of this
difference. A degree of proficiency in labyrinth B attained by the males
after 7.0 trials was equaled by the females after 6.2 trials. In labyrinth
C the males acquired a habit as a result of 18.7 trials; the females, as a
result of 13.8. And similarly in labyrinth D, 6.1 trials did no more for
the males than 5.9 did for the females.

That at the age of about one month the male dancer should be able to
acquire a visual discrimination habit more rapidly than the female,
whereas the female can acquire a labyrinth habit more readily than the
male, suggests an important difference in the nature of their equipment
for habit formation. One might hazard the suggestion that the male depends
more largely upon discrimination of external conditions, whereas the
female depends to a greater extent than does the male upon the internal,
organic changes which are wrought by acts. At any rate the female seems to
follow a labyrinth path more mechanically, more accurately, more easily,
and with less evidence of sense discrimination than does the male.

Finally, in concluding this chapter, I may add that in those aspects of
behavior which received attention in the early chapters of this volume the
dancers differ very markedly. Some climb readily on vertical or inclined
surfaces to which they can cling; others seldom venture from their
horizontally placed dance floor. Some balance themselves skillfully on
narrow bridges; others fall off almost immediately. My own observations,
as well as a comparison of the accounts of the behavior of the dancer
which have been given by Cyon, Zoth, and other investigators, lead me to
conclude that there are different kinds of dancing mice. This may be the
result of crosses with other species of mice, or it may be merely an
expression of the variability of an exceptionally unstable race.

I can see no satisfactory grounds for considering the dancer either
abnormal or pathological. It is a well-established race, with certain
peculiarities to which it breeds true; and no pathological structural
conditions, so far as I have been able to learn, have been discovered.

I have presented in this chapter on differences a program rather than a
completed study. To carry out fully the lines of work which have been
suggested by my observations and by the presentation of results would
occupy a skilled observer many months. I have not as yet succeeded in
accomplishing this, but my failure is not due to lack of interest or of



In a general way those peculiarities of behavior which suggested the name
dancing mouse are inherited. Generation after generation of the mice run
in circles, whirl, and move the head restlessly and jerkily from side to
side. But these forms of behavior vary greatly. Some individuals whirl
infrequently and sporadically; others whirl frequently and persistently,
at certain hours of the day. Some are unable to climb a vertical surface;
others do so readily. Some respond to sounds; others give no indications
of ability to hear. I propose in this chapter to present certain facts
concerning the inheritance of individual peculiarities of behavior, and to
state the results of a series of experiments by which I had hoped to test
the inheritance of individually acquired forms of behavior.

My study of the nature of the whirling tendency of the dancer has revealed
the fact that certain individuals whirl to the right almost uniformly,
others just as regularly to the left, and still others now in one
direction, now in the other. On the basis of this observation, the animals
have been classified as right, left, or mixed whirlers. Does the dancer
transmit to its offspring the tendency to whirl in a definite manner?

Records of the direction of whirling of one hundred individuals have been
obtained. For twenty of these mice the determination was made by counting
the number of complete turns in five-minute intervals at six different
hours of the day. For the remaining eighty individuals the direction was
discovered by observation of the activity of the animals for a brief
interval at five different times. Naturally, the former results are the
more exact; in fact, they alone have any considerable quantitative value.
But for the problem under consideration all of the determinations are
sufficiently accurate to be satisfactory.

The distribution of the individuals which were examined as to direction of
whirling is as follows.


Males 19 19 12 50
Females 12 23 15 50

The frequency of occurrence of left whirlers among the females is
unexpectedly high. Is this to be accounted for in terms of inheritance? In
my search for an answer to this question I followed the whirling tendency
from generation to generation in two lines of descent. These two groups of
mice have already been referred to as the 200 line and the 400 line. The
former were descended from Nos. 200 and 205, and the latter from Nos. 152
and 151. Individuals which resulted from the crossing of these lines will
be referred to hereafter as of mixed descent. There were some striking
differences in the behavior of the mice of the two lines of descent. As a
rule the individuals of the 200 line climbed more readily, were more
active, danced less vigorously, whirled less rapidly and less
persistently, and were in several other respects much more like common
mice than were the individuals of the 400 line. It is also to be noted
(see Table 5) that few of the litters of the 200 line exhibited auditory
reactions, whereas almost all of the litters of the 400 line which were
tested gave unmistakable evidence of sensitiveness to certain sounds.
These differences at once suggest the importance of an examination of the
whirling tendency of each line of descent.

The results for the several generations of each line which I had
opportunity to examine are unexpectedly decisive so far as the question in
point is concerned.



First generation No. 200, ? No. 205, ?
Second generation No. 210, Mixed whirler No. 215, Left whirler
Third generation No. 220, Mixed whirler No. 225, Mixed whirler
Fourth generation No. 230, Right whirler No. 235, Mixed whirler
Fifth generation No. 240, Right whirler No. 245, Left whirler



First generation No. 152, Left whirler No. 151, Left whirler
Second generation No. 410, Left whirler No. 415, Right whirler
Third generation No. 420, Left whirler No. 425, Left whirler

One line of descent exhibited no pronounced whirling tendency; the other
exhibited a strong tendency to whirl to the left. Are these statements
true for the group of one hundred individuals whose distribution among the
three classes of whirlers has been given? In order to obtain an answer to
this question I have reclassified these individuals according to descent
and direction of whirling.



Males 7 6 8 21
Females 5 8 8 21
12 14 16 42



Males 4 9 1 14
Females 6 9 4 19
10 18 5 33


9 10 6 25

Three interesting facts are indicated by these results: first, the
inheritance of a tendency to whirl to the left in the 400 line of descent;
second, the lack of any definite whirling tendency in the 200 line; and
third, the occurrence of right and left whirlers with equal frequency as a
result of the crossing of these two lines of descent.

It is quite possible, and I am inclined to consider it probable, that the
pure dancer regularly inherits a tendency to whirl to the left, and that
this is obscured in the case of the 200 line by the influences of a cross
with another variety of mouse. It is to be noted that the individuals of
the 200 line were predominantly mixed whirlers, and I may add that many of
them whirled so seldom that they might more appropriately be classed as


The white-black discrimination experiments which were made in connection
with the study of vision and the modifiability of behavior were so planned
that they should furnish evidence of any possible tendency towards the
inheritance of modifications in behavior. The problem may be stated thus.
If a dancing mouse be thoroughly trained to avoid black, by being
subjected to a disagreeable experience every time it enters a black box,
will it transmit to its offspring a tendency to avoid black?

Systematic training experiments were carried on with individuals of both
the 200 and 400 lines of descent. For each of these lines a male and a
female were trained at the age of four weeks to discriminate between the
white and the black electric-boxes and to choose the former. After they
had been thoroughly trained these individuals were mated, and in course of
time a male and female, chosen at random from their first litter, were
similarly trained. All the individuals were trained in the same way and
under as nearly the same conditions as could be maintained, and accurate
records were kept of the behavior of each animal and of the number of
errors of choice which it made in series after series of tests. What do
these records indicate concerning the influence of individually acquired
forms of behavior upon the behavior of the race?



Number of Errors in Daily Series of Ten Tests



No. 210 No. 220 No. 230 No. 240 No. 215 No. 225 No. 235 No. 245

A 6 5 6 7 8 4 4 7
B 6 8 8 8 8 7 6 5

1 6 7 6 5 7 6 5 4
2 4 3 1 5 5 6 4 5
3 3 1 4 5 3 4 4 3
4 5 0 3 4 2 1 3 1
5 3 0 4 2 1 3 3 0
6 2 1 4 2 2 1 1 1
7 1 0 3 1 1 1 2 0
8 0 0 1 0 0 0 2 3
9 0 0 0 1 1 0 0 0
10 0 0 1 0 2 1 1
11 0 0 0 3 0 0
12 0 0 0 0 0
13 0 0 0 0
14 0

I have records for four generations in the 200 line and for three
generations in the 400 line.[1] As the results are practically the same
for each, I shall present the detailed records for the former group alone.
In Table 53 are to be found the number of errors made in successive series
of ten tests each by the various individuals of the 200 line which were
trained in this experiment. The most careful examination fails to reveal
any indication of the inheritance of a tendency to avoid the black box.
No. 240, in fact, chose the black box more frequently in the preference
series than did No. 210, and he required thirty more tests for the
establishment of a perfect habit than did No. 210. Apparently descent from
individuals which had thoroughly learned to avoid the black box gives the
dancer no advantage in the formation of a white-black discrimination
habit. There is absolutely no evidence of the inheritance of this
particular individually acquired form of behavior in the dancer.

[Footnote 1: This experiment was interrupted by the death of the animals
of both lines of descent.]


Abnormal dancers.
Acquired forms of behavior.
Act, useless, repeated.
Activity, periods of.
Affirmation, choice by.
Age, peculiarities;
maximum age;
and intelligence.
Albino cat;
Alexander and Kreidl, young dancer;
tracks of mice;
behavior in cyclostat;
behavior of white mouse and dancer;
structure of ear;
Allen, G. M., drawing of dancer;
heredity in mice.
Alleys, width of, in labyrinths.
Amyl acetate for photometry.
Anatomy of dancer.
Animals, education of.
Appuun whistles.
Audition. _See_ Hearing.
Averages, dangers in.

Baginsky, B., model of ear of dancer.
Bateson, W., breeding experiments.
Behavior, of dancer;
inheritance of;
when blinded;
structural bases of;
of young;
changes in;
useless acts;
under experimental conditions;
in indiscriminable conditions;
value of sight;
in labyrinth experiments;
modifiability of;
history of;
explanations of;
individual differences in.
Blinded dancers, behavior of.
Blue-orange tests;
blue-red tests;
blue-green tests;
blue-green blindness.
Bradley papers.
Brain, structure of.
Breeding of dancers.
Brehm, A. E., "Tierleben".
Brightness vision;
check experiments;
relation to color vision.

Cages for dancers.
Candle meter.
Candle power.
Cardboards, for tests of vision;
positions of.
Care of dancer.
Castle, W. E., drawing of mouse;
Cat, albino;
training of.
Cerebellum of dancer.
Characters, acquired.
Check experiments.
China, dancers of.
Choice, exhibition of;
by affirmation;
by negation;
by comparison;
methods of.
Circling, a form of dance.
Circus course mice.
Cleghorn, A. G.
Climbing of dancer.
Cochlea, functions of.
Color blindness.
Color discrimination apparatus.
Colored glasses.
Colored papers.
Color patterns of dancers.
Color vision, problem;
methods of testing;
tests with colored papers,
tests with ray filters,
orange-blue tests,
yellow-red tests,
light blue-orange tests,
dark blue-red tests,
green-light blue tests,
violet-red tests,
green-blue tests,
green-red tests,
blue-green tests,
blue-red tests,
structure of the retina,
of different animals,
Comparative pedagogy,
Comparison, choice by,
Cones, lacking in eye of dancer,
Corti, organ of, in dancer,
Cotton mouse,
Curves, of habit formation,
irregularities of,
of labyrinth habit,
of discrimination habit,
of learning and re-learning,
of plasticity,
Cyclostat, behavior of dancer in,
Cyon, E. de, dancer pathological,
behavior of blinded dancers,
varieties of dancer,
space perception,
individual differences,
anatomy of dancer,
hearing of dancer,
pain cries.

Dancers, occurrence among common mice,
varieties of,
forms of dance movement,
whirling, circling, figure-eights, manege movements, solo
dance, centre dance,
direction of,
periods of,
amount of,
causes of,
sex differences in,
individual differences in,
Darbishire, A. D., breeding experiments with dancers,
Deafness of dancer,
causes of,
Descent, lines of,
Development of young dancer,
Differences, individual,
Direction of movement, choice by,
Direction of whirling,
Discrimination, visual, box,
of brightness,
white-black and black-white,
of grays,
by odor,
by form,
habit defined,
Diseases of dancer,
Dog, albino,
training of,
fear of electric shock.

Ear, structure of,
structural types,
model of,
of rabbit,
functions of,
movements of,
Educability of dancer,
Education, human,
methods of,
of vision,
Efficiency of training,
Electric-box for visual tests,
Electric-labyrinth for habit experiments,
Electric-shock as punishment for mistakes,
Epidemic among dancers,
Equilibration in dancer,
Error curves,
form of,
Error records versus time records,
Errors, in labyrinths,
nature of,
types of,
value of,
number of,
Even numbers to designate males,
Excitability of dancer,
Experience, value of,
influence of,
Eyes, of dancer
opening of
retina of

Fear, in dancer
designated by odd numbers
dancing of
voice of
_See_ Sex
Fighting of dancers
Figure eight dance
Filters for obtaining colored light
Food of dancer
Form discrimination
reactions of
repetition of act by
Functions of eye

Galton whistle
Gestation, period of, in dancer
Gray papers
Green blue tests
Green-red tests
Grouping for averages
Guaita, G von,
breeding experiments with dancers

Haacke, W,
description of dancer,
origin of dancer
breeding experiments
of dancing,
duration of,
reacquisition of,
relations of,
Habit formation,
and the senses,
_versus_ habit performance,
in the dancer and in the common mouse,
curves of,
speed of
Habituation to sounds
Hacker, dancing shrews
Hair, appearance of
Hamilton, G V, experiments with dog
Hatai, S, the dancer
Head, shape of, in dancer
in dancer
in young
in adult
methods of testing,
in frog
Hefner unit of light
_See_ Inheritance
Hering, E, colored papers
of dancer
of acts
Hunger as motive in experiments
Hybrid dancers

Imitation in dancer
Index of modifiability
Inhibition of an act
Initiative of dancer
Insight of dancer
measures of,
Interrupted circuit for experimental use
Irregular labyrinths

Janssen-Hoffman spectroscope
Japan, dancers in
Judgment in dancer

Kammerer, P, dancing wood mice,
Kishi, K,
dancer in Japan
origin of race,
blinded dancer,
structure of ear,
wax in ears,
tests of hearing
Koenig tuning forks,
steel bars
Kreidl, A
_See_ Alexander

forms of,
labyrinth A,
errors in,
labyrinth B,
labyrinth C,
labyrinth D,
a standard labyrinth,
regular and irregular labyrinths
Labyrinth errors and individual tendencies
Labyrinth habits,
Labyrinth method,
Labyrinth path, formula,
method of recording,
Ladder climbing tests,
Landois, H, account of dancer,
Lathrop, A, dancers,
Learning, process,
methods of in dancer,
by being put through act,
by imitation,
by rote,
rapidity of,
permanency of,
learning and relearning,
curves of,
Left whirlers,
Life span of dancer,
Light, reflected,
transmitted, unit of measurement,
control of,
Litter, size of, in dancer,
Lummer-Brodhun photometer.

Males, dancing of,
fighting and killing young, designation of,
voice of, _See_ Sex
Manege movements,
Mark, E L, cages,
Maze _See_ Labyrinth
Measurements, of light,
of rapidity of habit formation,
of intelligence,
of efficiency of training,
Memory, defined,
for ladder climbing,
tests of,
measurements of,
span of,
for brightness,
for color,
Method, of studying dance,
for testing hearing,
for testing vision,
for brightness vision,
for color vision,
of shifting filters,
of testing form discrimination,
of testing Weber's law,
development of methods,
of choice,
food box,
of recording errors,
of training
problem method, labyrinth method, discrimination method,
of recording labyrinth path,
qualitative versus quantitative,
of studying senses,
values of methods,
of measuring intelligence,
comparisons of,
Milne-Edwards, origin of dancer,
Mitsukun, K, the dancer in Japan,
Mixed whirlers,
Modifiability, of behavior,
of useless acts,
index of,
Motives, for activity,
for choice,
avoidance of discomfort,
in labyrinths,
desire to escape, to get food, to avoid pain,
Motor, tendencies,
of ears,
_Mus musculus L_,
_Mus spiciosus L_,
_Mus sylvaticus L_.

_Nankin nesumi_, name for dancer,
Negation, choice by,
Nendel, R, gray papers,
Nerve, eighth,
Nervous system,
Nest materials,
Noises, effects of,
Numbers, odd for females, even for males,
reference, _See_ Bibliographic List.

Odors, discrimination by,
Old Fancier's description of dancer,
Olfactory sense _See_ Smell
Orange-blue tests,
Orientation of dancer,
Origin of dancer;
by selectional breeding;
by inheritance of an acquired character;
by mutation;
by pathological changes;
by natural selection.

Panse, R.,
structure of ear;
explanation of deafness.
Papers, Nendel's grays;
Bradley's colored;
Hering's colored.
Parker, G. H.
Path in labyrinth, record of.
Pathological condition of dancer.
Pedagogy, comparative.
of brightness;
of color;
of movement;
of form.
Peru, dancers in.
Petromyzon, semicircular canals of.
Photometer, Lummer-Brodhun.
Plasticity of dancer;
curves of.
Position choice by,
of cardboards.
Preference for brightness,
tests of.
Preliminary tests.
Probable error.
Problems, of structure;
of method.
Punishment versus reward.
Putting-through, training by.

Qualitative methods.
Quantitative methods.

Rabbit, ear of.
Rawitz, B., behavior of dancer;
structure of ear;
deafness of dancer;
hearing in young.
Ray filters.
Reactions, to sounds;
to disagreeable stimuli;
Reasoning, implicit.
Reconstruction method.
Records, of markings of dancers;
of time;
of errors;
of path.
Red, stimulating value of;
Reference numbers to literature.
_See_ Literature on Dancer.
Reflected light.
Refrangibility and vision of dancer.
Regular labyrinth.
Re-learning, relation to learning;
curves of.
Reliability of averages.
Repetition of useless acts.
Restlessness, of dancer;
cause of.
Retina of dancer.
Retzius, ear of rabbit.
Reward, for performance of act;
versus punishment.
Right whirlers;
behavior in labyrinth;
occurrence of;
inheritance of tendency.
Rods of retina.
Rotational dizziness.
Rubber stamps of labyrinths.

Saint-Loup, R.
Schlumberger, C.;
wood carving with dancers.
Selenka, ear of rabbit.
Semicircular canals.
Sense organs.
Senses, and habit formation;
differences in.
Sex, recognition of, designation
of, peculiarities
Shellac to coat cards
Shrews, dancing
Sight, role of, _See_ Vision,
Brightness Vision, and Color Vision
Smell sense of, in labyrinth habits
Sniffing by dancer
Solutions as ray filters
_Sorex vulgaris L_
Sound, reactions to
Space perception
Spectrum, stimulating value of
Standard, candle, light,
Stine, W M, photometrical measurements
Strength of dancer
Structure, of brain,
of ear, of eye
Swinhoe, mice in China

Temperament of animal
Temperature sense
Tests, visual, number of,
per day,
Threshold of discrimination
Time records
Touch, and labyrinth habits
Training conditions of, Weber's
law, methods of,
and retraining, in labyrinths,
efficiency of, two test,
ten-test, twenty-test,
continuous, relation to
methods, spread of
Transmitted light.

Variability of dancer,
Variable light.
Varieties of dancer
Violet red tests
Vision, brightness
vision, color vision,
training of, importance
of, conclusions concerning
Visual dizziness
Voice of dancer

Watson, J B, habit formation
Waugh, K, color vision apparatus,
retina of mouse
Wax, plugs of, in ear of mouse
Weber's law, tests of, apparatus
Weldon, W F R, breeding experiments,
Whirling of dancer

Yellow Red tests
Young dancers, killing of, by male,
description of, development
of, hearing of, intelligence
of, size of

Zoth, O, origin of dancer, size
of young mice, the senses of
dancer, behavior, dancing,
equilibration, climbing
dancers, individual differences,
tests of hearing,

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