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The Dancing Mouse

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






TABLE 26

GREEN-RED TESTS

Brightnesses Different for Human Eye

No. 2 No. 5

SERIES DATE BRIGHTNESS RIGHT WRONG RIGHT WRONG
VALUES (GREEN) (RED) (GREEN) (RED)

1 May 7 Green
Red 1800 c.m. 10 10 12 8
2 8 Same 12 8 11 9
3 9 Same 15 5 14 6
4 10 Same 18 2 12 8
5 11 Same 18 2 14 6
6 12 Same 19 1 16 4
7 13 Same 19 1 18 2
8 14 Same 20 0 20 0


Brightness tests without colors were now given to determine whether the
mice had been choosing the brighter or the darker instead of the green.


TABLE 26--CONTINUED


NO. 2 NO. 5

SERIES DATE BRIGHTNESS VALUES RIGHT WRONG RIGHT WRONG
(GREEN) (RED) (GREEN) (RED)

8a 14 Brighter 74 c.m. 0[1] 10[2] 2[1] 8[2]
Darker 3 c.m.
9 15 3 c.m. on left
1800 c.m. on right 8 12 16 4
10 16 4 c.m. on left
36 c.m. on right 5 5 7 3
11 16 Green 4 c.m.
Red 36 c.m. 9 1 8 2
12 17 11 c.m. on left
1800 c.m. on right 7 3 6 4
13 17 Green 11 c.m.
Red 1800 c.m. 9 1 8 2
14 18 Mixed values
3 to 1800 c.m. 7 3 8 2
15 19 Same 7 3 7 3
16 20 Same 7 3 7 3
17 21 Same 7 3 9 1
18 22 Same 9 1 8 2
19 23 Same 7 3 9 1
20 24 Same 10 0 8 2
21 25 Same 10 0 9 1
22 26 Same 9 1 10 0


[Footnote 1: Brighter]
[Footnote 2: Darker]



Immediately after the brightness series, the influence of making first one
color, then the other, the brighter was studied. Throughout series 9 the
brightness value of the left box remained 3 candle meters, that of the
right side 1800 candle meters. Number 2 was so badly confused by this
change that his mistakes in this series numbered 12; No. 5 made only 4
incorrect choices. Then series after series was given under widely
differing conditions of illumination. The expression "mixed values," which
occurs in Table 26 in connection with series 14 to 22 inclusive, means
that the brightnesses of the green and the red boxes were changed from
test to test in much the way indicated by the sample series of Table 25.
In view of the results of these 22 series, 320 tests for each of two mice,
it is evident that the dancer is able to discriminate visually by some
other factor than brightness. What this factor is I am not prepared to
say. It may be something akin to our color experience, it may be distance
effect. No other possibilities occur to me.

Table 26 shows that discrimination was relatively easy for Nos. 2 and 5
with green at 3 candle meters and red at 1800. That their discrimination
was made on the basis of the greater brightness of the red, instead of on
the basis of color, is indicated by the results of the brightness check
series 8a. Increase in the brightness of the green rendered discrimination
difficult for a time, but it soon improved, and by no changes in the
relative brightness of the two colors was it possible to prevent correct
choice.

In addition to giving point to the statement that red appears darker to
the dancer than to us, the above experiment shows that the animals depend
upon brightness when they can, and that their ability to discriminate
color differences is extremely poor, so poor indeed that it is doubtful
whether their records are better than those of a totally color blind
person would be under similar conditions. Surely in view of such results
it is unsafe to claim that the dancer possesses color vision similar to
ours.

Perfectly trained as they were, by their prolonged green-red tests, to
choose the green, or what in mouse experience corresponds to our green,
Nos. 2 and 5 offered an excellent opportunity for further tests of blue-
green discrimination. For in view of their previous training there should
be no question of preference for the blue or of a tendency to depend upon
brightness in the series whose results constitute Table 27.


TABLE 27
BLUE-GREEN TESTS

NO. 2 NO. 5

SERIES DATE BRIGHTNESS VALUES RIGHT WRONG RIGHT WRONG
(BLUE) (GREEN) (BLUE) (GREEN)

1 June 1 Blue 74 c.m.
Green 36 c.m. 3 7 3 7
2 2 Same 5 5 4 6
3 3 Same 5 5 6 4
4 4 Same 6 4 3 7
5 5 Same 6 4 5 5
6 6 Blue 21 c.m.
Green 21 c.m. 6 4 7 3
7 7 Same 2 8 3 7
8 8 Same 5 5 4 6
9 9 Same 3 7 6 4
10 10 Same 2 8 4 6
11 12 Same 6 4 3 7
12 13 Blue 36 c.m.
Green 21 c.m. 3 7 4 6
13 14 Same 5 5
14 15 Blue 62 c.m.
Green 21 c.m. 4 6
15 16 Same 5 5
16 17 Same 5 5
17 18 Same 6 4




Now, as a final test, blue and green glasses were placed over the
electric-boxes, the brightness of the two was equalized for the human eye,
and the tests of series 18 and 19 were given to No. 2:--


TABLE 27--CONTINUED

NO. 2
SERIES DATE BRIGHTNESS VALUES
RIGHT WRONG
(Blue) (Green)

18 18 Blue 62 c.m.
Green 21 c.m 4 6
19 19 Same 6 4
20 20 Blue 21 c.m.
Green 88 c.m. 2 8


The green was now made much the brighter.


21 21 Blue 21 c.m.
Green 18 c.m. 7 3
22 23 Same 8 2


To begin with, the blue and the green were made quite bright for the human
subject, blue 74 candle meters, green 36. Later the brightness of both was
first decreased, then increased, in order to ascertain whether
discrimination was conditioned by the absolute strength of illumination.
No evidence of discrimination was obtained with any of the several
conditions of illumination in seventeen series of ten tests each.

On the supposition that the animals were blinded by the brightness of the
light which had been used in some of the tests, similar tests were made
with weaker light. The results were the same. I am therefore convinced
that the animals did justice to their visual ability in these experiments.

Finally, it seemed possible that looking directly at the source of light
might be an unfavorable condition for color discrimination, and that a
chamber flooded with colored light from above and from one end would prove
more satisfactory. To test this conjecture two thicknesses of blue glass
were placed over one electric-box, two plates of green glass over the
other; the incandescent lamps were then fixed in such positions that the
blue and the green within the two boxes appeared to the experimenter, as
he viewed them from the position at which the mouse made its choice, of
the same brightness.

Mouse No. 2 was given two series of tests, series 18 and 19, under these
conditions, with the result that he showed absolutely no ability to tell
the blue box from the green box. The opportunity was now taken to
determine how quickly No. 2 would avail himself of any possibility of
discriminating by means of brightness. With the blue at 21 candle meters,
the green was increased to about 1800. Immediately discrimination
appeared, and in the second series (22 of Table 27) there were only two
mistakes.

The results of the blue-green experiments with light transmitted from in
front of the animal and from above it are in entire agreement with those
of the experiments in which reflected light was used. Since the range of
intensities of illumination was sufficiently great to exclude the
possibility of blinding and of under illumination, it is necessary to
conclude that the dancer does not possess blue-green vision.

Again I must call attention to the fact that the behavior of the mice in
these experiments is even more significant of their lack of discriminating
ability than are the numerical results of the tables. After almost every
series of tests, whether or not it came out numerically in favor of
discrimination, I was forced to add the comment, "No satisfactory evidence
of discrimination."

We have now examined the results of green-red, green-blue, and blue-green
tests. One other important combination of the colors which were used in
these experiments is possible, namely, blue-red. This is the most
important of all the combinations in view of the results already
described, for these colors represent the extremes of the visible
spectrum, and might therefore be discriminable, even though those which
are nearer together in the spectral series were not.


TABLE 28
BLUE-RED TESTS



No. 2 No. 205
SERIES DATE BRIGHTNESS VALUES
RIGHT WRONG RIGHT WRONG
(BLUE) (RED) (BLUE) (RED)

1 July 31 1800 c.m. on left
24 c.m. on right 5 5 6 4
2 Aug. 1 21 c.m. on left
1800 c.m. on right 6 4 6 4
3 2 1800 c.m. on left
21 c.m. on right 8 2 6 4
4 3 19 c.m. on left
1800 c.m. on right 9 1 6 4
5 4 1800 c.m. on left
7 c.m. on right 7 3 5 5
6 5 6 c.m. on left
1800 c.m. on right 10 0 7 3
7 6 18 c.m. on left
74 c.m. on right 10 0 9 1
8 7 1800 c.m. on left
7 c.m. on right 8 2 8 2
9 8 7 c.m. on left
1800 c.m. on right 7 3 8 2
10 9 Mixed values
6 to 1800 c.m. 8 2 9 1
11 10 Blue 3 c.m.
Red 1800 c.m. 7 3 6 4


Brightness tests were now made, without the use of colors.

11a 10 4 6 5 5

12 10 Blue 3 c.m.
Red 8 c.m. 4 6 6 4
13 11 Blue 3 c.m.
Red 7200 c.m. 8 2 5 5
14 13 Mixed values
3 to 7200 c.m. 7 3 7 3
15 13 Same 7 3 9 1
16 14 Blue 3 to 6 c.m.
Red 112 to 3650 c.m. 10 0 10 0


Series were now given to test the assumption that red appears dark to the
dancer.



17 14 Darkness on one side
Red 3 c.m. 5 5 7 3
18 14 Blue 3 to 3650 c.m.
Red 3 to 3650 c.m. 10 0 10 0
19 15 Darkness on one side
Red 3 c.m. 5 5 4 6
20 15 Blue 3 to 3650 c.m.
Red 3 to 3650 c.m. 10 0 9 1
21 16 Darkess on one side
Red 72 c.m. 5 5 7 3
22 16 Darkness on one side
Red 1800 c.m. 6 4 10 0


As is shown by the results in Table 28, no combination of brightnesses
rendered correct choice impossible in the case of the blue-red tests which
are now to be described. Choice was extremely difficult at times, even
more so perhaps than the table would lead one to suppose, and it is quite
possible that color played no part in the discrimination. But that
brightness difference in the colors was not responsible for whatever
success these mice attained in selecting the right box is proved by the
brightness-without-color series which follows series II of the table.
Neither No. 2 nor No. 205 showed preference for the lighter or the darker
box. At the end of the sixteenth blue-red series, I was convinced that one
of two conclusions must be drawn from the experiment: either the dancers
possess a kind of blue-red vision, or red is of such a value for them that
no brightness of visible green or blue precisely matches it.

The latter possibility was further tested by an experiment whose results
appear in series 17 to 22 inclusive, of Table 28. The conditions of series
17 were a brightness value of 0 in one box (darkness) and in the other red
of a brightness of 3 candle meters. Despite the fact that they had been
perfectly trained in _blue-red tests_ to avoid the red, neither of the
mice seemed able to discriminate the red from the darkness and to avoid
it. This was followed by a series in which the brightness of both the blue
and the red was varied between 3 and 3650 candle meters, with the striking
result that neither mouse made any mistakes. In series 19 red was used
with darkness as in series 17, and again there was a total lack of
discrimination. Series 20 was a repetition of series 18, with practically
the same result. I then attempted to find out, by increasing the
brightness of the red, how great must be its value in order that the
dancers should distinguish it readily from darkness. For the tests of
series 21 it was made 72 candle meters, but discrimination did not clearly
appear. At 1800 candle meters, as is shown in series 22, the red was
sufficiently different in appearance from total darkness to enable No. 205
to discriminate perfectly between the two electric-boxes. For No. 2
discrimination was more difficult, but there was no doubt about his
ability. It would appear from these tests that the dancers had not learned
to avoid red. Therefore we are still confronted with the question, can
they see colors?



TABLE 29

VISUAL CHECK TESTS
With the Electric-boxes Precisely Alike Visually


No. 151 No. 152
SERIES DATE
RIGHT WRONG RIGHT WRONG

1 Sept. 29 6 4 4 6
2 30 5 5 6 6
3 Oct. 1 3 7 4 6
4 2 5 5 3 7
5 3 3 7 5 5
6 4 6 4 5 5
7 5 5 5 5 5
8 6 -- -- 3 7
9 7 -- -- 6 4
10 8 -- -- 4 6

Averages 4.7 5.3 4.5 5.5



The account of my color vision experiments is finished. If it be objected
that other than visual conditions may account for whatever measure of
discriminating ability, apart from brightness discrimination, appears in
some of the series, the results of the series of Table 29, in which all
conceivable visual means of discrimination were purposely excluded, and
those of the several check tests which have been described from time to
time in the foregoing account, should furnish a satisfactory and definite
answer. I am satisfied that whatever discrimination occurred was due to
vision; whether we are justified in calling it color vision is quite
another question.

I conclude from my experimental study of vision that although the dancer
does not possess a color sense like ours, it probably discriminates the
colors of the red end of the spectrum from those of other regions by
difference in the stimulating value of light of different wave lengths,
that such specific stimulating value is radically different in nature from
the value of different wave lengths for the human eye, and that the red of
the spectrum has a very low stimulating value for the dancer. In the light
of these experiments we may safely conclude that many, if not most, of the
tests of color vision in animals which have been made heretofore by other
investigators have failed to touch the real problem because the
possibility of brightness discrimination was not excluded.

Under the direction of Professor G. H. Parker, Doctor Karl Waugh has
examined the structure of the retina of the dancing mouse for me, with the
result that only a single type of retinal element was discovered.
Apparently the animals possess rod-like cells, but nothing closely similar
to the cones of the typical mammalian retina. This is of peculiar interest
and importance in connection with the results which I have reported in the
foregoing pages, because the rods are supposed to have to do with
brightness or luminosity vision and the cones with color vision. In fact,
it is usually supposed that the absence of cones in the mammalian retina
indicates the lack of color vision. That this inference of functional
facts from structural conditions is correct I am by no means certain, but
at any rate all of the experiments which I have made to determine the
visual ability of the dancer go to show that color vision, if it exists at
all, is extremely poor. It is gratifying indeed to learn, after such a
study of behavior as has just been described, that the structural
conditions, so far as we are able to judge at present, justify the
conclusions which have been drawn.




CHAPTER XI

THE ROLE OF SIGHT IN THE DAILY LIFE OF THE DANCER

Darting hither and thither in its cage, whirling rapidly, now to the left,
now to the right, running in circles, passing through holes in the nest
box quickly and neatly, the dancer, it would seem, must have excellent
sight. But careful observation of its behavior modifies this inference.
For it appears that a pair of mice dancing together, or near one another,
sometimes collide, and that it is only those holes with which the animal
is familiar that are entered skillfully. In fact, the longer one observes
the behavior of the dancer under natural conditions, the more he comes to
believe in the importance of touch, and motor tendencies. Sight, which at
first appears to be the chief guiding sense, comes to take a secondary
place. In this chapter it is my purpose to show by means of simple
experiments what part sight plays in the dancer's life of habit formation.

The evidence on this subject has been obtained from four sources: (1)
observation of the behavior of dancers in their cages; (2) observation of
their behavior when blinded; (3) observation of their behavior in a great
variety of discrimination experiments, many of which have already been
described; and (4) observation of their behavior in labyrinth experiments
which were especially planned to exhibit the importance of the several
kinds of vision which the dancer might be supposed to possess. The
evidence from the first three of these sources may be presented summarily,
for much of it has already appeared in earlier chapters. That from the
fourth source will constitute the bulk of the material of this chapter.

My observation of the behavior of the mice has furnished conclusive
evidence of their ability to see moving objects. But that they do not see
very distinctly, and that they do not have accurate perception of the form
of objects, are conclusions which are supported by observations that I
have made under both natural and experimental conditions. In Chapters VII,
VIII, IX, and X, I have presented an abundance of evidence of brightness
vision and, in addition, indications of a specific sensitiveness to wave
length which may be said to correspond to our color vision. It is
noteworthy, however, that all of the experimental proofs of visual ability
were obtained as the result of long periods of training. Seldom, indeed,
in my experience with them, have the dancers under natural conditions
exhibited forms of activity which were unquestionably guided by vision.

It is claimed by those who have experimented with blinded dancers that the
loss of sight decreases the amount and rapidity of movement, and the
ability of the animals to avoid obstacles.

By means of the discrimination method previously used in the preliminary
experiments on color vision, a full description of which may be found in
Chapter IX, p. 133, the dancers' ability to perceive form was tested.
Immediately after the two males _A_ and _B_ had been given the "food-box"
tests, whose results appear in Table 15, they were tested in the same
apparatus and by the same method for their ability to discriminate a
rectangular food-box from a round one. In the case of the color
discrimination tests, it will be remembered that the circular tin boxes 5
cm. in diameter by 1.5 cm. in depth, one of which was covered with blue
paper, the other with orange, were used. For the form discrimination tests
I used instead one of the circular boxes of the dimensions given above and
a rectangular box 8.5 cm. long, 5.5 cm. wide and 2.5 cm. deep. "Force" was
placed in the circular box. The tests were given, in series of 20, daily.



TABLE 30

VISUAL FORM TESTS

SERIES DATE MOUSE A MOUSE B
RIGHT WRONG RIGHT WRONG
(CIRCULAR (RECTANGU- (CIRCULAR (RECTANGU-
BOX) LAR BOX) BOX) LAR BOX)
1 Jan. 5 10 10 9 11
2 7 12 8 13 7
3 10 6 14 10 10
4 11 7 13 10 10
5 12 9 11 10 10
6 13 11 9 11 9
7 14 13 7 9 11
8 15 10 10 11 9
9 16 10 10 11 9
10 17 11 9 9 11
11 18 11 9 12 8
12 19 12 8 10 10
13 20 10 10 12 8
14 21 10 10 8 12
15 22 10 10 10 10

Totals 152 148 155 145



The results of 15 series of these tests, as may be seen by the examination
of Table 30, are about as definitely negative, so far as form
discrimination is in question, as they possibly could be. From the first
series to the last there is not one which justifies the inference that
either of the dancers depended upon the form of the boxes in making its
choice. In view of the general criticisms I have made concerning the use
of hunger as a motive in experiments on animal behavior, and in view of
the particular criticisms of this very method of testing the
discriminating powers of the mouse, it may seem strange that space should
be given to a report of these tests. I sympathize with the feeling, if any
one has it, but, at the same time, I wish to call attention to the fact
that almost any mammal which is capable of profiting by experience, and
which, under the same conditions, could distinguish the rectangular box
from the circular one, would have chosen the right box with increasing
accuracy as the result of such experience. The results are important in my
opinion, not because they either prove or disprove the ability of the
dancer to discriminate these particular forms, the discrimination of which
might fairly be expected of any animal with an image-forming eye, but
because they demonstrate an important characteristic of the dancing mouse,
namely, its indifference to the straightforward or direct way of doing
things.

Most mammals which have been experimentally studied have proved their
eagerness and ability to learn the shortest, quickest, and simplest route
to food without the additional spur of punishment for wandering. With the
dancer it is different. It is content to be moving; whether the movement
carries it directly towards the food is of secondary importance. On its
way to the food-box, no matter whether the box be slightly or strikingly
different from its companion box, the dancer may go by way of the wrong
box, may take a few turns, cut some figure-eights, or even spin like a top
for seconds almost within vibrissa-reach of the food-box, and all this
even though it be very hungry. Activity is pre-eminently important in the
dancer's life.

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