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The Dancing Mouse

R >> Robert M. Yerkes >> The Dancing Mouse




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
animal.

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).



TABLE 41

WHITE BLACK DISCRIMINATION TESTS. NUMBER OF ERRORS IN
THE VARIOUS SERIES

MALES FEMALES

AVERAGES AVERAGES GENERAL AVERAGES AVERAGES GENERAL AVERAGES
SERIES FOR 5, FOR 5, AVERAGES FOR 5, FOR 5, AVERAGES FOR ALL
10 TESTS 20 TESTS FOR 10 10 TESTS 20 TESTS FOR 10 (20) MALES
PER DAY PER DAY PER DAY PER DAY AND FEMALES

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.




CHAPTER XV


THE EFFICIENCY OF TRAINING METHODS

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
experiments.

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
explanation.

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
active.

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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