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The Dancing Mouse

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




[Illustration: FIGURE 15.--Ground plan of discrimination box. _A_, nest-
box; _B_, entrance chamber; _W,W_, electric-boxes; _L_, doorway of left
electric-box; _R_, doorway of right electric-box; _E_, exit from electric-
box to alley; _I_, swinging door between _A_ and _B_; _O_, swinging door
between alley and _A_; _IC_, induction apparatus; _C_, electric cell; _K_,
key in circuit.]

An opportunity for visual discrimination by brightness difference was
provided by placing dead black cardboard at the entrance and on the inside
of one of the electric-boxes, as shown in Figure 14, _B_, and white
cardboard similarly in the other box. These cardboards were movable and
could be changed from one box to the other at the will of the
experimenter. The test consisted in requiring the mouse to choose a
certain brightness, for example, the white cardboard side, in order to
return to the nest-box without receiving an electric shock. The question
which the experimenter asked in connection with this test really is, Can a
dancer learn to go to the white box and thus avoid discomfort? If we
assume its ability to profit by experience within the limits of the number
of experiences which it was given, such a modification of behavior would
indicate discrimination of brightness. Can the dancer distinguish white
from black; light gray from dark gray; two grays which are almost of the
same brightness? The results which make up the remainder of this and the
following chapter furnish a definite answer to these questions.

To return to the experimental procedure, the mouse which is being tested
is placed by the experimenter in the nest-box, where frequently in the
early tests food and a comfortable nest were attractions. If it does not
of its own accord, as a result of its abundant random activity, pass
through _I_ into _B_ within a few seconds, it is directed to the doorway
and urged through. A choice is now demanded of the animal; to return to
the nest-box it must enter either the white electric-box or the black one.
Should it choose the white box, it is permitted to return directly to _A_
by way of the doorway _E_, the alley, and the swinging door at _O_, and it
thus gets the satisfaction of unobstructed activity, freedom to whirl, to
feed, and to retreat for a time to the nest. Should it choose to attempt
to enter the black box, as it touches the wires of the interrupted circuit
it receives a shock as a result of the closing of the key in the circuit
by the experimenter, and further, if it continues its forward course
instead of retreating from the "stinging" black box, its passage through
_E_ is blocked by a barrier of glass temporarily placed there by the
experimenter, and the only way of escape to the nest-box is an indirect
route by way of _B_ and the white box. Ordinarily the shock was given only
when the mouse entered the wrong box, not when it retreated from it; it
was never given when the right box was chosen. The box to be chosen,
whether it was white, gray, or black, will be called the right box. The
electric shock served as a means of forcing the animal to use its
discriminating ability. But the question of motives in the tests is not so
simple as might appear from this statement.

The reader will wonder why the mouse should have any tendency to enter
_B_, and why after so doing, it should trouble to go further, knowing, as
it does from previous experiences, that entering one of the electric-boxes
may result in discomfort. The fact is, a dancer has no very constant
tendency to go from _A_ to _B_ at the beginning of the tests, but after it
has become accustomed to the box and has learned what the situation
demands, it shows eagerness to make the trip from _A_ to _B_, and thence
by way of either the right or the left route to _A_. That the mouse should
be willing to enter either of the electric-boxes, after it has experienced
the shock, is even more surprising than its eagerness to run from _A_ to
_B_. When first tested for brightness discrimination in this apparatus, a
dancer usually hesitated at the entrance to the electric-boxes, and this
hesitation increased rapidly unless it were able to discriminate the boxes
by their difference in brightness and thus to choose the right one. During
the period of increasing hesitancy in making the choice, the experimenter,
by carefully moving from _I_ toward the entrances to the electric-boxes a
piece of cardboard which extended all the way across _B_, greatly
increased the mouse's desire to enter one of the boxes by depriving it of
dancing space in _B_. If an individual which did not know which entrance
to choose were permitted to run about in _B_, it would often do so for
minutes at a time without approaching the entrance to the boxes; but the
same individual, when confined to a dancing space 4 or 5 cm. wide in front
of the entrances, would enter one of the electric-boxes almost
immediately. This facilitation of choice by decrease in the amount of
space for whirling was not to any considerable extent the result of fear,
for all the dancers experimented with were tame, and instead of forcing
them to rush into one of the boxes blindly and without attempt at
discrimination, the narrowing of the space simply increased their efforts
to discriminate. The common mouse when subjected to similar experimental
conditions is likely to be frightened by being forced to approach the
entrances to the boxes, and fails to choose; it rushes into one box
directly, and in consequence it is as often wrong as right. The dancer
always chooses, but its eagerness to choose is markedly increased by the
restriction of its movements to a narrow space in front of the entrances
between which it is required to discriminate. It is evident that the
animal is uncomfortable in a space which is too narrow for it to whirl in
freely. It must have room to dance. This furnished a sufficiently strong
motive for the entering of the electric-boxes. It must avoid disagreeable
and unfavorable stimuli. This is a basis for attempts to choose, by visual
discrimination, the electric-box in which the shock is not given. It may
safely be said that the success of the majority of the experiments of this
book depended upon three facts: (1) the dancer's tendency to avoid
disagreeable external conditions, (2) its escape-from-confinement-
impelling need of space in which to dance freely, and (3) its abundant and
incessant activity.

Of these three conditions of success in the experiments, the second and
third made possible the advantageous use of the first. For the avoidance
of a disagreeable stimulus could be made use of effectively in the tests
just because the mice are so restless and so active. In fact their
eagerness to do things is so great that the experimenter, instead of
having to wait for them to perform the desired act, often is forced to
make them wait while he completes his observation and record. In this
respect they are unlike most other animals.

My experiments with the dancer differ from those which have been made by
most students of mammalian behavior in one important respect. I have used
punishment instead of reward as the chief motive for the proper
performance of the required act. Usually in experiments with mammals
hunger has been the motive depended upon. The animals have been required
to follow a certain devious path, to escape from a box by working a
button, a bolt, a lever, or to gain entrance to a box by the use of teeth,
claws, hands, or body weight and thus obtain food as a reward. There are
two very serious objections to the use of the desire for food as a motive
in animal behavior experiments--objections which in my opinion render it
almost worthless in the case of many mammals. These are the discomfort of
the animal and the impossibility of keeping the motive even fairly
constant. However prevalent the experience of starvation may be in the
life of an animal, it is not pleasant to think of subjecting it to extreme
hunger in the laboratory for the sake of finding out what it can do to
obtain food. Satisfactory results can be obtained in an experiment whose
success depends chiefly upon hunger only when the animal is so hungry that
it constantly does its best to obtain food, and when the desire for food
is equally strong and equally effective as a spur to action in the
repetitions of the experiment day after day. It is easy enough to get
almost any mammal into a condition of utter hunger, but it is practically
impossible to have the desire for food of the same strength day after day.
In short, the desire for food is unsatisfactory as a motive in animal
behavior work, first, because a condition of utter hunger, as has been
demonstrated with certain mammals, is unfavorable for the performance of
complex acts, second, because it is impossible to control the strength of
the motive, and finally, because it is an inhumane method of
experimentation.

In general, the method of punishment is more satisfactory than the method
of reward, because it can be controlled to a greater extent. The
experimenter cannot force his subject to desire food; he can, however,
force it to discriminate between conditions to the best of its knowledge
and ability by giving it a disagreeable stimulus every time it makes a
mistake. In other words, the conditions upon which the avoidance of a
disagreeable factor in the environment depends are far simpler and much
more constant than those upon which the seeking of an agreeable factor
depends. Situations which are potentially beneficial to the animal attract
it in varying degrees according to its internal condition; situations
which are potentially disagreeable or injurious repel it with a constancy
which is remarkable. The favorable stimulus solicits a positive response;
the unfavorable stimulus demands a negative response.

Finally, in connection with the discussion of motives, it is an important
fact that forms of reward are far harder to find than forms of punishment.
Many animals feed only at long intervals, are inactive, do not try to
escape from confinement, cannot be induced to seek a particular spot, in a
word, do not react positively to any of the situations or conditions which
are employed usually in behavior experiments. It is, however, almost
always possible to find some disagreeable stimulus which such an animal
will attempt to avoid.

As it happens, the dancer is an animal which does not stand the lack of
food well enough to make hunger a possible motive. I was driven to make
use of the avoiding reaction, and it has proved so satisfactory that I am
now using it widely in connection with experiments on other animals. The
use of the induction shock, upon which I depended almost wholly in the
discrimination experiments with the dancer, requires care; but I am
confident that no reasonable objection to the conduct of the experiments
could be made on the ground of cruelty, for the strength of the current
was carefully regulated and the shocks were given only for an instant at
intervals. The best proof of the humaneness of the method is the fact that
the animals continued in perfect health during months of experimentation.

The brightness discrimination tests demanded, in addition to motives for
choice, adequate precautions against discrimination by other than visual
factors, and, for that matter, by other visual factors than that of
brightness. The mouse might choose, for example, not the white or the
black box, but the box which was to the right or to the left, in
accordance with its experience in the previous test. This would be
discrimination by position. As a matter of fact, the animals have a strong
tendency at first to go uniformly either to the right or to the left
entrance. This tendency will be exhibited in the results of the tests.
Again, discrimination might depend upon the odors of the cardboards or
upon slight differences in their shape, texture, or position. Before
conclusive evidence of brightness discrimination could be obtained, all of
these and other possibilities of discrimination had to be eliminated by
check tests. I shall describe the various precautions taken in the
experiments to guard against errors in interpretation, in order to show
the lengths to which an experimenter may be driven in his search for
safely interpretable results.

To exclude choice by position, the cardboards were moved from one
electric-box to the other. When the change was made regularly, so that
white was alternately on the right and the left, the mouse soon learned to
go alternately to the right box and the left without stopping to notice
the visual factor. This was prevented by changing the position of the
cardboards irregularly.

Discrimination by the odor, texture, shape, and position of the cardboards
was excluded by the use of different kinds of cardboards, by changing the
form and position of them in check tests, and by coating them with
shellac.

The brightness vision tests described in this chapter were made in a room
which is lighted from the south only, with the experiment box directed
away from the windows. The light from the windows shone upon the
cardboards at the entrances to the electric-boxes, not into the eyes of
the mouse as it approached them. Each mouse used in the experiments was
given a series of ten tests in succession daily. The experiment was
conducted as follows. A dancer was placed in _A_, where it usually ran
about restlessly until it happened to find its way into _B_. Having
discovered that the swing door at _I_ could be pushed open, the animal
seemed to take satisfaction in passing through into _B_ as soon as it had
been placed in or had returned to _A_. In _B_, choice of two entrances,
one of which was brighter than the other, was forced by the animal's need
of space for free movement. If the right box happened to be chosen, the
mouse returned to _A_ and was ready for another test; if it entered the
wrong box, the electric shock was given, and it was compelled to retreat
from the box and enter the other one instead. In the early tests with an
individual, a series sometimes covered from twenty to thirty minutes; in
later tests, provided the condition of discrimination was favorable, it
did not occupy more than ten minutes.

To exhibit the methods of keeping the records of these experiments and
certain features of the results, two sample record sheets are reproduced
below. The first of these sheets, Table 6, represents the results given by
No. 5, a female,[1] in her first series of white-black tests. Table 7
presents the results of the eleventh series of tests given to the same
individual.

[Footnote 1: It is to be remembered that the even numbers always designate
males; the odd numbers, females.]

In the descriptions of the various visual experiments of this and the
following chapters, the first word of the couplet which describes the
condition of the experiment, for example, white-black, always designates
the visual condition which the animal was to choose, the second that which
it was to avoid on penalty of an electric shock. In the case of Tables 6
and 7, for example, white cardboard was placed in one box, black in the
other, and the animal was required to enter the white box. In the tables
the first column at the left gives the number of the test, the second the
positions of the cardboards, and the third and fourth the result of the
choice. The first test of Table 6 was made with the white cardboard on the
box which stood at the left of the mouse as it approached from _A_, and,
consequently, with the black cardboard on the right. As is indicated by
the record in the "wrong" column, the mouse chose the black instead of the
white. The result of this first series was choice of the white box four
times as compared with choice of the black box six times. On the eleventh
day, that is, after No. 5 had been given 100 tests in this brightness
vision experiment, she made no mistakes in a series of ten trials (Table
7).


TABLE 6

BRIGHTNESS DISCRIMINATION

White-Black, Series 1

Experimented on No. 5 January 15, 1906
POSITION OF
TEST CARDBOARDS RIGHT WRONG

1 White left -- Wrong
2 White right -- Wrong
3 White left -- Wrong
4 White right -- Wrong
5 White left Right --
6 White right Right --
7 White left -- Wrong
8 White right Right --
9 White left -- Wrong
10 White right Right --

Totals 4 6


Before tests, such as have been described, can be presented as conclusive
proof of discrimination, it must be shown that the mouse has no preference
for the particular brightness which the arrangement of the test requires
it to select. That any preference which the mouse to be tested might have
for white, rather than black, or for a light gray rather than a dark gray,
might be discovered, what may be called preference test series were given
before the discrimination tests were begun. These series, two of which
were given usually, consisted of ten tests each, with the white
alternately on the left and on the right. The mouse was permitted to enter
either the white or the black box, as it chose, and to pass through to the
nest-box without receiving a shock and without having its way blocked by
the glass plate. The conditions of these preference tests may be referred
to hereafter briefly as "No shock, open passages." The preference tests,
which of course would be valueless as such unless they preceded the
training tests, were given as preliminary experiments, in order that the
experimenter might know how to plan his discrimination tests, and how to
interpret his results.



TABLE 7

BRIGHTNESS DISCRIMINATION

White-Black, Series II

Experimented on No. 5 February 2, 1906

POSITION
TEST OF CARDBOARDS RIGHT WRONG

1 White left Right --
2 White left Right --
3 White right Right --
4 White right Right --
5 White right Right --
6 White left Right --
7 White left Right --
8 White left Right --
9 White right Right --
10 White right Right --

Totals 10 0



The results given in the white-black preference tests by ten males and ten
females are presented in Table 8. Three facts which bear upon the
brightness discrimination tests appear from this table: (1) black is
preferred by both males and females, (2) this preference is more marked in
the first series of tests than in the second, and (3) it is slightly
stronger for the first series in the case of females than in the case of
males.


TABLE 8

WHITE-BLACK PREFERENCE TESTS

MALES FIRST SERIES SECOND SERIES
WHITE BLACK WHITE BLACK

No. 10 3 7 3 7
18 5 5 5 5
20 2 8 4 6
152 4 6 6 4
210 4 6 4 6
214 6 4 3 7
220 5 5 3 7
230 4 6 2 8
410 4 6 5 5
420 4 6 9 1

Averages 4.1 5.9 4.4 5.6


FEMALES FIRST SERIES SECOND SERIES
WHITE BLACK WHITE BLACK

No. 11 5 5 4 6
151 6 4 5 5
215 2 8 2 8
213 2 8 5 5
225 4 6 2 8
227 4 6 6 4
235 6 4 4 6
415 2 8 4 6
425 5 5 8 2
229 2 8 5 5

Averages 3.8 6.2 4.5 5.5


That the dancers should prefer to enter the dark rather than the light box
is not surprising in view of the fact that the nests in which they were
kept were ordinarily rather dark. But whatever the basis of the
preference, it is clear that it must be taken account of in the visual
discrimination experiments, for an individual which strongly preferred
black might choose correctly, to all appearances, in its first black-white
series. Such a result would demonstrate preference, and therefore one kind
of discrimination, but not the formation of a habit of choice by
discrimination. The preference for black is less marked in the second
series of tests because the mouse as it becomes more accustomed to the
experiment box tends more and more to be influenced by other conditions
than those of brightness. The record sheets for both series almost
invariably indicate a strong tendency to continue to go to the left or the
right entrance according to the way by which the animal escaped the first
time. This cannot properly be described as visual choice, for the mouse
apparently followed the previous course without regard to the conditions
of illumination. We have here an expression of the tendency to the
repetition of an act. It is only after an animal acquires considerable
familiarity with a situation that it begins to vary its behavior in
accordance with relatively unimportant factors in the situation. It is
this fact, illustrations of which may be seen in human life, as well as
throughout the realm of animal behavior, that renders it imperative that
an animal be thoroughly acquainted with the apparatus for experimentation
and with the experimenter before regular experiments are begun. Any animal
will do things under most experimental conditions, but to discover the
nature and scope of its ability it is necessary to make it thoroughly at
home in the experimental situation. As the dancer began to feel at home in
the visual discrimination apparatus it began to exercise its
discriminating ability, the first form of which was choice according to
position.

Since there appears to be a slight preference on the part of most dancers'
for the black box in comparison with the white box, white-black training
tests were given to fifty mice, and black-white to only four. The tests
with each individual were continued until it had chosen correctly in all
of the tests of three successive series (thirty tests). As the
reproduction of all the record sheets of these experiments would fill
hundreds of pages and would provide most readers with little more
information than is obtainable from a simple statement of the number of
right and wrong choices, only the brightness discrimination records of
Tables 6 and 7 are given in full.

As a basis for the comparison of the results of the white-black tests with
those of the black-white tests, two representative sets of data for each
of these conditions of brightness discrimination are presented (Tables 9
and 10). In these tables only the number of right and wrong choices for
each series of ten tests appears.

Tables 9 and 10 indicate--if we grant that the precautionary tests to be
described later exclude the possibility of other forms of discrimination--
that the dancer is able to tell white from black; that it is somewhat
easier, as the preference tests might lead us to expect, for it to learn
to go to the black than to the white, and that the male forms the habit of
choosing on the basis of brightness discrimination more quickly than the
female.



TABLE 9
WHITE-BLACK TESTS


No. 210 No. 215
AGE, 28 DAYS AGE, 28 DAYS
SERIES DATE RIGHT WRONG RIGHT WRONG
(WHITE) (BLACK) (WHITE) (BLACK)
A June 22 4 6 2 8
B 23 4 6 2 8

1 24 4 6 3 7
2 25 6 4 5 5
3 26 7 3 7 3
4 27 5 5 8 2
5 28 7 3 9 1
6 29 8 2 8 2
7 30 9 1 9 1
8 July 1 10 0 10 0
9 2 10 0 9 1
10 3 10 0 10 0
11 4 -- -- 10 0
12 5 -- -- 10 0




TABLE 10
WHITE-BLACK TESTS

No. 14 No. 13
AGE, 32 DAYS AGE, 32 DAYS
SERIES DATE RIGHT WRONG RIGHT WRONG
(WHITE) (BLACK) (WHITE) (BLACK)
1 May 13[1] 5 5 7 3
2 14 8 2 6 4
3 15 7 3 9 1
4 16 9 1 9 1
5 17 10 0 10 0
6 18 10 0 9 1
7 19 10 0 10 0
8 20 -- -- 10 0
9 21 -- -- 10 0

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