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The Dancing Mouse

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




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

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

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

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

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

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

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

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

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


TABLE 31

THE ROLE OF SIGHT

Labyrinth-B Experiments


NO. 7 NO. 998

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





TABLE 32

LABYRINTH-B EXPERIMENTS

with

Electric Shock given as Punishment for Mistakes

No. 7 No. 998
TEST DATE CONDITION ERRORS CONDITION ERRORS


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




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

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

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

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

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

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

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

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

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

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

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

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

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

VII. A final test in darkness completed the series.

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

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

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


TABLE 33

THE ROLE OF SIGHT, TOUCH, AND SMELL IN LABYRINTH EXPERIMENTS


No. 210 No. 215

TEST CONDITION ERRORS CONDITION ERRORS

I. 1 No shock 9 I. No shock 2

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

9 Shock 0 III. Labyrinth 0
moved

10 Shock 0 IV. Paper on floor 4

III. 11 Labyrinth 0 No paper (shock) 0
moved

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




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

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

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

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


TABLE 34

ROLE OF SIGHT, TOUCH, AND SMELL IN LABYRINTH EXPERIMENTS


II. IV.
TRAINING TESTS SMOKED
I. NO OF TESTS BEFORE III. PAPER ON
MALES PRELIMINARY CORRECT LABYRINTH FLOOR
TEST. _____________________ MOVED. NO OF TIMES
ERRORS FIRST TIME FIVE TIMES ERRORS BEFORE COR-
RECT TWICE

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

AVERAGES 11.2 5.7 14.5 .3 10.8

FEMALES

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

AVERAGES 9.2 5.5 12.5 .3 9.5



V.
DARKNESS VI.
MALES LABYRINTH VII.
ERRORS IN NO. OF TESTS WASHED. DARKNESS.
FIRST TEST BEFORE COR'CT ERRORS ERRORS

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

Averages 1.2 2.5 1.2 0.8

FEMALES

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

Averages 1.5 2.8 0.7 1.0




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

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

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

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

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

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

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