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The Dancing Mouse

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






TABLE 42

EFFICIENCY OF TRAINING. WHITE-BLACK TESTS AT THE RATE
OF 2 OR 5 PER DAY

MALES FEMALES
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




TABLE 43

EFFICIENCY OF TRAINING. WHITE-BLACK TESTS AT THE RATE OF
10 PER DAY

MALES FEMALES
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




TABLE 44

EFFICIENCY OF TRAINING. WHITE-BLACK TESTS AT THE RATE OF
20 PER DAY

MALES FEMALES
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.



TABLE 45

EFFICIENCY OF TRAINING. WHITE-BLACK TESTS AT THE RATE OF
100 OR MORE PER DAY

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
superfluous.

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.



TABLE 46

EFFICIENCY OF TRAINING

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

SETS OF 10 2 OR 5 TESTS 10 TESTS 20 TESTS 100 OR MORE
PER DAY PER DAY PER DAY TESTS PER DAY

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:--



METHOD INDEX OF MODIFIABILITY (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.



TABLE 47

EFFICIENCY OF TRAINING

CONDITION MALES FEMALES
INDEX OF MODIFIABILITY INDEX OF MODIFIABILITY
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.




CHAPTER XVI

THE DURATION OF HABITS: MEMORY AND RE-LEARNING

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.



TABLE 48

MEASUREMENTS OF THE DURATION OF A HABIT

Memory

ERRORS
NO. AGE NAME OF TEST REST FIRST FIRST SECOND
INTERVAL CHOICE SERIES SERIES

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.

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