A B C D E F G H I J K L M N O P R S T U V W X Z

The Dancing Mouse

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




1 Dec. 6 -- -- -- --
2 7 -- -- -- --
3 8 12 8 12 8
4 9 10 10 9 11
5 10 15 5 10 10
6 11 10 10 12 8
7 12 9 11 9 11
8 13 10 10 9 11
9 14 12 8 12 8
10 15 13 7 12 8
11 16 13 7 10 10
12 17 12 8 10 10
13 18 11 9 10 10
14 19 13 7 8 12
15 20 13 7 9 11
16 22 14 6 12 8
17 23 10 10 9 11

TOTALS 177 123 153 147




In preliminary tests, at the rate of four per day, the colored cardboards
were placed only at the entrances to the boxes, not inside, and as was
true also in the case of brightness tests under like conditions, no
evidence of discrimination was obtained from ten days' training. This
seemed to indicate that a considerable area of the colored surface should
be exposed to the mouse's view, if discrimination were to be made
reasonably easy.

This conclusion was supported by the results of other preliminary
experiments in which rectangular pieces of colored papers[1] 6 by 3 cm.,
were placed on the floor at the entrances to the electric-boxes, instead
of on the walls of the boxes. Mouse No. 2 was given five series of ten
tests each with a yellow card to indicate the right box and a red card at
the entrance to the wrong box. At first he chose the red almost uniformly,
and at no time during these fifty tests did he exhibit ability to choose
the right box by color discrimination. I present the results of these
series in Table 16, because they indicate a fact to which I shall have to
refer repeatedly later, namely, that the brightness values of different
portions of the spectrum are not the same for the dancer as for us.
Previous to this yellow-red training, No. 2, as a result of ten days of
white-black training (two tests per day), had partially learned to go to
the brighter of the two electric-boxes. It is possible therefore that the
choice of the box in the case of these color experiments was in reality
the choice of what appeared to the mouse to be the brighter box. If this
were not true, how are the results of Table 16 to be accounted for?

[Footnote 1: These were the only Hering papers used in my experiments.]

TABLE 16

YELLOW-RED TESTS

In Color Discrimination Box with 6 by 3 cm. Pieces of Hering
Papers at Entrances to Boxes

No. 2

SERIES DATE RIGHT WRONG
1906 (Yellow) (Red)
1 Jan. 16 1 9
2 17 3 7
3 18 4 6
4 19 5 5
5 20 5 5



Without further mention of the many experiments which were necessary for
the perfecting of this method of testing color vision, I may at once
present the final results of the tests which were made with reflected
light. These tests were made with the discrimination apparatus in
essentially the same way as were the brightness discrimination tests of
Chapter VII.

In all of the color experiments, unless otherwise stated, a series of ten
tests each day was given, until satisfactory evidence of discrimination or
proof of the lack of the ability to discriminate had been obtained. The
difficulties of getting conclusive evidence in either direction will be
considered in connection with the results themselves. For all of these
tests with reflected light the Milton Bradley colored papers were used.
These colored papers were pasted on white cardboard carriers. I shall
designate, in the Bradley nomenclature, the papers used in each
experiment.

With colored cardboards inside the electric-boxes as well as at their
entrances (see Figure 14 for position of cardboards) blue-orange tests
were given to Nos. 2 and 3 until they discriminated perfectly. The papers
were Bradley's blue tint No. 1 and orange. Number 2 was perfect in the
twelfth series (Table 17), No 3 in the fourteenth and again in the
sixteenth. They were then tested with a special brightness check series
which was intended by the experimenter to reveal any dependence upon a
possible brightness difference rather than upon the color difference of
the boxes.



TABLE 17

LIGHT BLUE-ORANGE TESTS IN COLOR DISCRIMINATION BOX

SERIES DATE NO. 2 NO. 3
1906 RIGHT WRONG RIGHT WRONG
(LIGHT (ORANGE) (LIGHT (ORANGE)
BLUE) BLUE)


1 Jan. 26 7 3 1 9
2 27 7 3 5 5
3 28 7 3 6 4
4 29 7 3 7 3
5 30 7 3 4 6
6 31 10 0 7 3
7 Feb. 1 9 1 7 3
8 2 8 2 6 4
9 3 9 1 9 1
10 5 7 3 5 5
11 6 8 2 5 5
12 7 10 0 5 5
Special brightness check series (see Table 18)
13 8 10 0 7 3
Special light blue-dark blue series
14 9 8 2 10 0
15 10 9 1 9 1
Special light blue-dark blue series
16 11 9 1 10 0
Special brightness
check series
17 12 10 0 9 1




TABLE 18

LIGHT BLUE-ORANGE

Brightness check series Mouse No. 2, Series 13
Feb. 8, 1906

TEST CONDITION RIGHT WRONG

1 Light blue on right
Orange on left Right ____

2 Light blue on left
Orange on right Right ____

3 Light blue on right
Red substituted for orange Right ____

4 Light blur on left
Red substituted for orange Right ____

5 Dark blue on right
Orange on left Right ____

6 Dark blue on left
Orange on right Right ____

7 Dark blue on left
Orange on right Right ____

8 Dark blue on right
Red substituted for orange Right ____

9 Dark blue on left
Red substituted for orange Right ____

10 Dark blue on left
Red substituted for orange Right ____

Totals 10 0



The nature of this brightness check series, as well as the results which
No. 2 gave when tested by it, may be appreciated readily by reference to
Table 18. Tint No. 1 of the blue, which is considerably brighter, in my
judgment, than the Bradley blue, was replaced at intervals in this series
by the latter. For it was thought that in case the mouse were choosing the
blue of the series because it seemed brighter than the orange, this
substitution might mislead it into choosing the orange. These blues are
referred to in the table as light blue (tint No. 1) and dark blue
(standard blue). Again a change in the opposite direction was made by
substituting Bradley red for orange. As this was for the human eye the
substitution of a color whose brightness was considerably less than that
of the orange, it seemed possible that the mouse, if it had formed the
habit of choosing the box which seemed the darker, might by this change be
misled into choosing the red instead of the light blue. In a word, changes
in the conditions of the experiments were made in such a way that now one
color, now the other, appeared to be the brighter. But I did not attempt
to exclude brightness discrimination on the part of the mouse by
dependence upon the human judgment of brightness equality, for it is
manifestly unsafe to assume that two colors which are of the same
brightness for the human eye have a like relation for the eye of the
dancer or of any other animal. My tests of color vision have been
conducted without other reference to human standards of judgment or
comparisons than was necessary for the description of the experimental
conditions. In planning the experiments I assumed neither likeness nor
difference between the human retinal processes and those of the dancer. It
was my purpose to discover the nature of the mouse's visual discriminative
ability.

As is indicated in the tables, neither the substitution of dark blue for
light blue, nor the replacement of the orange by red or dark blue rendered
correct choice impossible, although certain of the combinations did render
choice extremely difficult. In other words, despite all of the changes
which were made in the brightness of the cardboards in connection with the
light blue-orange tests, the mice continued to make almost perfect
records. What are we to conclude from this? Either that the ability to
discriminate certain colors is possessed by the dancer, or that for some
reason the tests are unsatisfactory. If it be granted that the possibility
of brightness discrimination was excluded in the check series, the first
of these alternatives apparently is forced upon us. That such a
possibility was not excluded, later experiments make perfectly clear. The
fact was that not even in the check series was the brightness value of the
orange as great as that of the blue. Consequently the mice may have chosen
the brighter box each time while apparently choosing the blue.

Although conclusive proof of the truth of this statement is furnished only
by later experiments, the results of the light blue-orange series, as
given in Table 17, strongly suggest such a possibility. Mouse No. 3 had
not been experimented with previous to these color discrimination tests.
Her preference for the orange, which in the case of the first series was 9
to 1, consequently demands an explanation. If she had been trained
previously to choose the white instead of the black, as was true of No. 2,
it might be inferred that she went to the orange box because it appeared
brighter than the blue. As this explanation is not available, we are
driven back upon the results of the white-black preference tests in
Chapter VII, which proved that many dancers prefer the black to the white.
This may mean that they prefer the lower degree of brightness or
illumination, and if so it might be argued, in turn, that the orange was
chosen by No. 3 because it appeared darker than the blue. Since, as has
already been stated, the orange was far brighter for me than the blue,
this would also mean that the brightness values of different colors are
not the same for man and mouse.

Practically the same kind of color tests as those described for Nos. 2 and
3 were given to Nos. 1000 and 5. The results appear in Table 19. These
tests followed upon the formation of a habit to choose white instead of
black (that is, the greater brightness). From the first both No. 1000 and
No. 5 chose the light blue in preference to the orange or the red. It
therefore seems probable that the former was considerably brighter than
the latter. Number 1000, to be sure, was led into three erroneous choices
by the brightness check series (series 7), but, on the other hand, No. 5
was not at all disturbed in her choices by similar check tests. It seems
natural to conclude from these facts that both of these mice chose the
blue at first because of its relatively greater brightness, and that they
continued to do so for the same reason. In other words, their behavior
indicates that the brightness check tests were valueless because not
enough allowance had been made for the possible differences between the
vision of mouse and man.


TABLE 19
LIGHT BLUE-ORANGE AND DARK BLUE-RED TESTS
No. 1000 No. 5
SERIES DATE Condition Right Wrong Right Wrong
(Light (Orange (Light (Orange
Blue or or Blue or
Dark Red) Dark Red)
Blue) Blue)
1 Jan. 25 Blue-red 8 2 10 0
2 26 Blue-red or
Light blue-orange 10 0 10 0
3 27 Light blue-orange 10 0 5 5
4 29 Light blue-orange 9 1 8 2
5 30 Light blue-orange 10 0 8 2
6 31 Light blue-orange 10 0 10 0
7 Feb. 1 Light blue-orange
or Dark blue-red 7 3 10 0


If only the final results of my experiments with the dancer and the
conclusions to which they lead were of interest, all of this description
of experiments which served merely to clear the ground and thus make
possible crucial tests might be omitted. It has seemed to me, however,
that the history of the investigation is valuable, and I am therefore
presenting the evolution of my methods step by step. To be sure, not every
detail of this process can be mentioned, and only a few of the individual
results can be stated, but my purpose will have been fulfilled if I
succeed in showing how one method of experimentation pointed the way to
another, and how one set of results made possible the interpretation of
others.

As the results of my color vision experiments seemed to indicate that the
red end of the spectrum appears much darker to the dancer than to us,
tests were now arranged with colors from adjacent regions of the spectrum,
green and blue. The papers used were the Bradley green and tint No. 1 of
the blue. They were not noticeably different in brightness for the human
eye. Green marked the box to be chosen. Three of the individuals which had
previously been used in the light blue-orange series, and which therefore
had perfect habits of going to the light blue, were used for the green-
light blue tests. Of these individuals, No. 1000 became inactive on the
fifth day of the experiment, and the tests with him were discontinued.
Twenty series were given to each of the other mice, with the results which
appear in Table 20. To begin with, both No. 4 and No. 5 exhibited a
preference for the light blue, as a result of the previous light blue-
orange training. As this preference was gradually destroyed by the
electric shock which was received each time the light blue box was
entered, they seemed utterly at a loss to know which box to enter.
Occasionally a record of six, seven, or even eight right choices would be
made in a series, but in no case was this unquestionably due to color
discrimination; usually it could be explained in the light of the order of
the changes in the positions of the cardboards. For example, series 9, in
which No. 5 made a record of 8 right and 2 wrong, had green on the right
for the first three tests. The animal happened to choose correctly in the
first test, and continued to do so three times in succession simply
because there was no change in the position of the cardboards. I have
occasionally observed a record of seven right choices result when it was
perfectly evident to the observer that the mouse could not discriminate
visually. It was to avoid unsafe conclusions and unfair comparisons, as
the result of such misleading series, that three perfect series in
succession were required as evidence of a perfectly formed habit of
discrimination.


TABLE 20

GREEN-LIGHT BLUE TESTS

Date No. 1000 No. 4 No. 5
SERIES 1906 RIGHT WRONG RIGHT WRONG RIGHT WRONG
(GREEN) (BLUE) (GREEN) (BLUE) (GREEN) (BLUE)

1 Feb.3 2 8 3 7 3 7

2 5 7 3 5 5 5 5

3 6 5 5 6 4 5 5

4 7 5 5 5 5 5 5

5 8 2 8 5 5 4 6

6 9 7 3 7 3

7 10 4 6 3 7

8 10 6 4 4 6

9 12 6 4 8 2

10 13 6 4 6 4

11 14 5 5 3 7

12 15 6 4 7 3

13 16 5 5 7 3

14 17 3 7 6 4

15 19 6 4 6 4

16 20 7 3 5 5

17 21 4 6 8 2

18 22 3 7 4 6

19 23 6 4 4 6

20 24 6 4 5 5



Twenty series, 200 tests for each of the individuals in the experiment,
yielded no evidence whatever of the dancer's ability to tell green from
blue. As it has already been proved that they readily learn to choose the
right box under discriminable conditions, it seems reasonable to conclude
either that they lack green-blue vision, or that they have it in a
relatively undeveloped state.

If it be objected that the number of training tests given was too small,
and that the dancer probably would exhibit discrimination if it were given
1000 instead of 200 tests in such an experiment, I must reply that the
behavior of the animal in the tests is even more satisfactory evidence of
its inability to choose than are the results of Table 20. Had there been
the least indication of improvement as the result of 200 tests, I should
have continued the experiment; as a matter of fact, the mice each day
hesitated more and more before choosing, and fought against being driven
toward the entrance to the experiment box. That they were helpless was so
evident that it would have been manifestly cruel to continue the
experiment.


TABLE 21
VIOLET-RED TESTS
With Odor of All Cardboards the Same

SERIES DATE NO. 7 NO. 998
RIGHT WRONG RIGHT WRONG
(VIOLET) (RED) (VIOLET) (RED)
A MAR. 7 8 2 5 5
B 7 3 7 2 8
1 14 3 7 6 4
2 15 4 6 4 6
3 16 5 5 5 5
4 19 4 6 4 6
5 20 5 5 6 4
6 21 4 6 8 2
7 22 8 2 4 6
8 23 4 6 6 4
9 24 6 4 4 6
10 25 4 6 6 4



Further color tests with reflected light were made with violet and red.
Two dancers, Nos. 998 and 7, neither of which had been in any experiment
previously, were subjected to the ten series of tests whose results are to
be found in Table 21. In this experiment the cardboards used had been
coated with shellac to obviate discrimination by means of odor. It is
therefore impossible to give a precise description of the color or
brightness by referring to the Bradley papers.[1] Both the violet and the
red were rendered darker, and apparently less saturated, by the coating.

[Footnote 1: The violet was darker than Bradley's shade No. 2, and the red
was lighter than Bradley's red.]

These violet-red tests were preceded by two series of preference tests
(_A_ and _B_), in which no shock was given and escape was possible through
either electric-box. Although the results of these preference tests as
they appear in Table 21 seem to indicate a preference for the red on the
part of No. 998, examination of the record sheets reveals the fact that
neither animal exhibited color preference, but that instead both chose by
position. Number 998 chose the box on the right 15 times in 20, and No. 7
chose the box on the left 15 times in 20.

Ten series of tests with the violet-red cardboards failed to furnish the
least indication of discrimination. The experiment was discontinued
because the mice had ceased to try to discriminate and dashed into one or
the other of the boxes on the chance of guessing correctly. When wrong
they whirled about, rushed out of the red box and into the violet
immediately. They had learned perfectly as much as they were able to learn
of what the experiment required of them. Although we are not justified in
concluding from this experiment that dancers cannot be taught to
distinguish violet from red, there certainly is good ground for the
statement that they do not readily discriminate between these colors.

The experiments on color vision which have been described and the records
which have been presented will suffice to give the reader an accurate
knowledge of the nature of the results, only a few of which could be
printed, and of the methods by which they were obtained.

In brief, these results show that the dancer, under the conditions of the
experiments, is not able to tell green from blue, or violet from red. The
evidence of discrimination furnished by the light blue-orange tests is not
satisfactory because the conditions of the experiment did not permit the
use of a sufficiently wide range of brightnesses. It is obvious,
therefore, that a method of experimentation should be devised in which the
experimenter can more fully control the brightness of the colors which he
is using. I shall now describe a method in which this was possible.




CHAPTER X

THE SENSE OF SIGHT: COLOR VISION (_Continued_)

There are three well-known ways in which colors may be used as stimuli in
experiments on animals: by the use of colored papers (reflected light); by
the use of a prism (the spectrum which is obtained may be used as directly
transmitted or as reflected light); and by the use of light filters
(transmitted light). In the experiments on the color vision of the dancer
which have thus far been described only the first of these three methods
has been employed. Its advantages are that it enables the experimenter to
work in a sunlit room, with relatively simple, cheap, and easily
manipulated apparatus. Its chief disadvantages are that the brightness of
the light can neither be regulated nor measured with ease and accuracy.
The use of the second method, which in many respects is the most desirable
of the three, is impracticable for experiments which require as large an
illuminated region as do those with the mouse; I was therefore limited to
the employment of light filters in my further tests of color
discrimination.

The form of filter which is most conveniently handled is the colored
glass, but unfortunately few glasses which are monochromatic are
manufactured. Almost all of our so-called colored glasses transmit the
light of two or more regions of the spectrum. After making spectroscopic
examinations of all the colored glasses which were available, I decided
that only the ruby glass could be satisfactorily used in my experiments.
With this it was possible to get a pure red. Each of the other colors was
obtained by means of a filter, which consisted of a glass box filled with
a chemical solution which transmitted light of a certain wave length.

For the tests with transmitted light the apparatus of Figures 20 and 21
was constructed. It consisted of a reaction-box essentially the same as
that used in the brightness vision tests, except that holes were cut in
the ends of the electric-boxes, at the positions _G and R_ of Figure 20,
to permit the light to enter the boxes. Beyond the reaction-box was a long
light-box which was divided lengthwise into two compartments by a
partition in the middle. A slit in the cover of each of these compartments
carried an incandescent lamp _L_ (Figure 20). Between the two lamps, _L,
L_, and directly over the partition in the light-box was fastened a
millimeter scale, _S_, by means of which the experimenter could determine
the position of the lights with reference to the reaction-box. The light-
box was separated from the reaction-box by a space 6 cm. wide in which
moved a narrow wooden carrier for the filter boxes. This carrier, as shown
in Figure 20, could be moved readily from side to side through a distance
of 20 cm. The filter boxes, which are represented in place in Figures 20
and 21, consisted of three parallel-sided glass boxes 15 cm. long, 5 cm.
wide, and 15 cm. deep. Each box contained a substance which acted as a ray
filter. Tightly fitted glass covers prevented the entrance of dust and the
evaporation of the solutions in the boxes. Figures 20 and 21 represent the
two end boxes, _R, R_, as red light filters and the middle one, _G_, as a
green light filter. Three filters were used thus side by side in order
that the position of a given color with reference to the electric-boxes
might be changed readily. As the apparatus was arranged, all the
experimenter had to do when he wished to change from green-left, red-right
to green-right, red-left was to push the carrier towards the right until
the green filter covered the hole on the right at the end of the electric-
box. When this had been accomplished the red filter at the left end of the
carrier covered the hole on the left at the end of the electric-box. Thus
quickly, noiselessly, easily, and without introducing any other change in
conditions than that of the interchange of lights, the experimenter was
able to shift the positions of his colored lights at will.

Copyright (c) 2007. famouswriterz.com. All rights reserved.