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




In Table 2 the results of the counts for the males are recorded; in Table
3 those for the females. Each number in the column headed "right" and
"left" indicates the total number of circles executed by a certain dancer
in a period of five minutes at the hour of the day named at the head of
the column. I may point out briefly the curiously interesting and entirely
unexpected new facts which this method of observation revealed to me.

First, there are three kinds of dancers: those which whirl almost
uniformly toward the right, those which whirl just as uniformly toward the
left, and those which whirl about as frequently in one direction as in the
other. To illustrate, No. 2 of Table 2 may be characterized as a "right
whirler," for he turned to the right almost uniformly. In the case of the
6 P.M. count, for example, he turned 285 times to the right, not once to
the left. No. 152, on the contrary, should be characterized as a "left
whirler," since he almost always turned to the left. From both of these
individuals No. 210 is distinguished by the fact that he turned now to the
left, now to the right. For him the name "mixed whirler" seems
appropriate.

Second, the amount of activity, as indicated by the number of times an
individual turns in a circle within five minutes, increases regularly and
rapidly from 9 A.M. to 8 P.M. According to the general averages which
appear at the bottom of Table 2, the average number of circles executed by
the males at 9 A.M. was 89.8 as compared with 207.1 at 8 P.M. In other
words, the mice dance more in the evening than during the day.

Third, as it appears in a comparison of the general averages of Tables 2
and 3, the females dance more than the males, under the conditions of
observation. At 9 A.M. the males circled 89.8 times, the females 151.0
times; at 8 P.M. the males circled 207.1 times, the females, 279.0 times.

Fourth, according to the averages for the six counts made with each
individual, as they appear in Table 4, the males turn somewhat more
frequently to the left than to the right (the difference, however, is not
sufficient to be considered significant); whereas, the females turn much
more frequently to the right than to the left. I do not wish to emphasize
the importance of this difference, for it is not improbable that counts
made with a larger number of animals, or even with another group of
twenty, would yield different results.



TABLE 2

NUMBER or WHIRLS TO THE RIGHT AND TO THE LEFT DURING
FIVE-MINUTE INTERVALS AS DETERMINED BY COUNTS MADE AT
SIX DIFFERENT HOURS, FOR EACH OF TEN MALE DANCERS


NUMBER 9 A.M 11 A.M. 2 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT

2 11 2 23 4 194 1
30 20 1 134 1 109 2
34 2 16 2 48 4 92
36 194 21 180 11 143 65
152 7 48 3 171 6 79
156 63 8 53 9 27 6
210 3 9 7 41 225 21
220 168 105 39 43 47 5
410 2 67 10 27 8 103
420 15 142 5 214 16 238

Averages 48.5 41.3 45.6 56.9 77.9 61.2

Gen. Av. 89.8 102.5 139.1


NUMBER 4 P.M 6 P.M. 8 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT

2 70 3 285 0 237 10
30 154 0 107 6 134 5
34 7 158 5 118 6 147
36 173 14 170 11 325 19
152 0 91 16 210 9 223
156 85 2 72 26 139 26
210 159 18 31 82 47 201
220 45 38 78 17 69 33
410 9 155 9 394 24 94
420 18 243 16 291 3 320

Averages 72.0 72.2 78.9 115.5 99.3 107.8

Gen. Av. 144.2 194.4 207.1






TABLE 3

NUMBER OF WHIRLS TO THE RIGHT AND TO THE LEFT DURING
FIVE-MINUTE INTERVALS AS DETERMINED BY COUNTS MADE AT
SIX DIFFERENT HOURS, FOR EACH OF TEN FEMALE DANCERS


NUMBER 9 A.M. 11 A.M. 2 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT

29 9 18 17 30 7 22
33 287 0 329 1 352 3
35 48 15 198 46 208 14
151 13 88 7 75 3 167
157 57 6 50 45 53 12
211 218 21 31 55 66 5
215 67 216 33 105 37 226
225 46 39 72 49 143 44
415 23 0 156 0 34 3
425 43 296 12 201 12 210

Averages 81.1 69.9 90.5 60.7 91.5 70.6

Gen. Av. 151.0 151.2 162.1

NUMBER 4 P.M. 6 P.M. 8 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT

29 33 114 31 36 45 99
33 436 7 408 3 364 2
35 279 6 165 24 353 10
151 3 8 2 285 2 217
157 52 15 19 125 51 104
211 190 7 86 31 67 250
215 15 292 45 336 150 232
225 133 86 48 39 177 81
415 268 3 437 7 382 8
425 12 242 19 210 4 192

Averages 142.1 78.0 126.0 109.6 159.5 119.5

Gen. Av. 220.1 235.6 279.0



The most important results of this statistical study of turning are the
demonstration of the existence of individual tendencies to turn in a
particular direction, and of the fact that the whirling increases in
amount from morning to evening.

In order to discover whether the distribution of the dancers among the
three groups which have been designated as right, left, and mixed whirlers
agrees in general with that indicated by Table 4 (approximately the same
number in each group) I have observed the direction of turning in the case
of one hundred dancers, including those of the foregoing tables, and have
classified them in accordance with their behavior as is indicated below.



RIGHT LEFT MIXED
WHIRLERS WHIRLERS WHIRLERS

Males 19 19 12
Females 12 23 15

Totals 31 42 27



The left whirlers occur in excess of both the right and the mixed
whirlers. This fact, together with the results which have already been
considered in connection with the counts of turning, suggests that a
tendency to whirl in a certain way may be inherited. I have examined my
data and conducted breeding experiments for the purpose of ascertaining
whether this is true. But as the results of this part of the investigation
more properly belong in a special chapter on the inheritance of behavior
(XVIII), the discussion of the subject may be closed for the present with
the statement that the preponderance of left whirlers indicated above is
due to a strong tendency to turn to the left which was exhibited by the
individuals of one line of descent.



TABLE 4

AVERAGE NUMBER OF WHIRLS TO THE RIGHT AND TO THE LEFT FOR
THE SIX INTERVALS OF TABLES 2 AND 3, WITH A CHARACTERIZATION
OF THE ANIMALS AS RIGHT WHIRLERS, LEFT WHIRLERS, OR
MIXED WHIRLERS.


AVERAGE NO. AVERAGE NO.
MALES AGE OF WHIRLS OF WHIRLS CHARACTERIZATION

2 12 mo. 136.7 3.3 Right whirler
30 2 mo. 109.7 2.5 Right whirler
34 2 mo. 4.3 96.5 Left whirler
36 2 mo. 197.5 23.5 Right whirler
152 6 mo. 6.8 137.0 Left whirler
156 1 mo. 73.2 12.8 Right whirler
210 3 mo. 78.7 62.0 Mixed whirler
220 4 mo. 74.3 40.2 Mixed whirler
410 3 mo. 10.3 139.0 Left whirler
420 3 mo. 12.2 241.3 Left whirler

Average 70.4 75.8 4 Right whirlers
4 Left whirlers
2 Mixed whirlers


FEMALES

29 2 mo. 23.7 53.2 Left whirler
33 2 mo. 362.7 2.7 Right whirler
35 2 mo. 208.5 19.2 Left whirler
151 6 mo. 5.0 140.0 Right whirler
157 1 mo. 47.0 51.2 Left whirler
211 3 mo. 109.7 61.5 Right whirler
215 3 mo. 57.8 234.5 Mixed whirler
225 4 mo. 103.2 56.3 Mixed whirler
415 3 mo. 216.7 3.5 Left whirler
425 3 mo. 17.0 225.2 Left whirler

Average 115.1 84.7 3 Right whirlers
4 Left whirlers
3 Mixed whirlers



The tendency of the dancer's activity to increase in amount toward
evening, which the results of Tables 2, 3, and 4 exhibit, demands further
consideration. Haacke (7 p. 337) and Kishi (21 p. 458) agree that the
dancing is most vigorous in the evening; but Alexander and Kreidl (i p.
544) assert, on the contrary, that the whirling of the individuals which
they observed bore no definite relation to the time of day and apparently
was not influenced in intensity thereby. Since the results of my own
observations contradict many of the statements made by the latter authors,
I suspect that they may not have watched their animals long enough to
discover the truth. The systematic records which I have kept indicate that
the mice remain quietly in their nests during the greater part of the day,
unless they are disturbed or come out to obtain food. Toward dusk they
emerge and dance with varying intensity for several hours. I have seldom
discovered one of them outside the nest between midnight and daylight. The
period of greatest activity is between 5 and 10 o'clock P.M.

Zoth states that he has observed the adult dancer whirl 79 times without
an instant's interruption, and I have counted as many as 110 whirls. It
seems rather absurd to say that an animal which can do this is weak.
Evidently the dancer is exceptionally strong in certain respects, although
it may be weak in others. Such general statements as are usually made fail
to do justice to the facts.

The supposition that light determines the periodicity of dancing is not
borne out by my observations, for I have found that the animals continue
to dance most vigorously toward evening, even when they are kept in a room
which is constantly illuminated. In all probability the periodicity of
activity is an expression of the habits of the mouse race rather than of
the immediate influence of any environmental condition. At some time in
the history of the dancer light probably did have an influence upon the
period of activity; but at present, as a result of the persistence of a
well-established racial tendency, the periodicity of dancing depends to a
greater extent upon internal than upon external conditions. During its
hours of quiescence it is possible to arouse the dancer and cause it to
whirl more or less vigorously by stimulating it strongly with intense
light, a weak electric current, or by placing two individuals which are
strangers to one another in the same cage; but the dancing thus induced is
seldom as rapid, varied, or as long-continued as that which is
characteristic of the evening hours.

One of the most interesting results of this study of the direction of
turning, from the observer's point of view, is the demonstration of the
fact that the truth concerning even so simple a matter as this can be
discovered only by long and careful observation. The casual observer of
the dancer gets an impression that it turns to the left more often than to
the right; he verifies his observation a few times and then asserts with
confidence that such is the truth about turning. That such a method of
getting knowledge of the behavior of the animal is worse than valueless is
clear in the light of the results of the systematic observations which
have just been reported. But, however important the progress which we may
have made by means of systematic observation of the phenomenon of turning,
it must not for one moment be supposed that the whole truth has been
discovered. Continued observation will undoubtedly reveal other important
facts concerning circling, whirling, and the periodicity of dancing, not
to mention the inheritance of peculiarities of dancing and the
significance of the various forms of activity.



CHAPTER IV

BEHAVIOR: EQUILIBRATION AND DIZZINESS


Quite as interesting and important as the general facts of behavior which
we have been considering are the results of experimental tests of the
dancer's ability to maintain its position under unusual spatial
conditions--to climb, cross narrow bridges, balance itself on high places.
Because of its tendency to circle and whirl, to dart hither and thither
rapidly and apparently without control of its movements, the study of the
mouse's ability to perform movements which demand accurate and delicate
muscular coördination, and to control its expressions of activity, are of
peculiar scientific interest.

That observers do not entirely agree as to the facts in this field is
apparent from the following comparison of the statements made by Cyon and
Zoth (31 p. 174).

Cyon states that the dancer


Cannot run in a straight line,
Cannot turn in a narrow space,
Cannot run backward,
Cannot run up an incline,
Cannot move about safely when above the ground, because of
fear and visual dizziness,
Can hear certain tones.


Zoth, on the contrary, maintains that the animal


Can run in a straight line for at least 20 cm.,
Can and repeatedly does turn in a narrow space,
Can run backward, for he has observed it do so,
Can run up an incline unless the surface is too smooth for it to
gain a foothold,
Can move about safely when above the ground, and gives no
signs of fear or dizziness,
Cannot hear, or at least gives no signs of sensitiveness to sounds.



Such contradictory statements (and unfortunately they are exceedingly
common) stimulated me to the repetition of many of the experiments which
have been made by other investigators to test the dancer's behavior in
unusual spatial relations. I shall state very briefly the general
conclusions to which these experiments have led me, with only sufficient
reference to methods and details of results to enable any one who wishes
to repeat the tests for himself to do so. For the sake of convenience of
presentation and clearness, the facts have been arranged under three
rubrics: equilibrational ability, dizziness, and behavior when blinded. To
our knowledge of each of these three groups of facts important
contributions have come from the experiments of Cyon (9 p. 220), Alexander
and Kreidl (1 p. 545), Zoth (31 p. 157), and Kishi (21 p. 482), although,
as has been stated, in many instances their results are so contradictory
as to demand reexamination. All in all, Zoth has given the most
satisfactory account of the behavior and motor capacity of the dancer.

If the surface upon which it is moving be sufficiently soft or rough to
furnish it a foothold, the dancer is able to run up or down inclines, even
though they be very steep, to cross narrow bridges, to balance itself at
heights of at least 30 cm. above the ground, and even to climb up and down
on rods, as is shown by certain of Zoth's photographs which are reproduced
in Figure 4. Zoth himself says, and in this I am able fully to agree with
him on the basis of my own observations, "that the power of equilibration
in the dancing mouse, is, in general, very complete. The seeming reduction
which appears under certain conditions should be attributed, not to visual
dizziness, but in part to excitability and restlessness, and in part to a
reduced muscular power" (31 p. 161). The dancer certainly has far less
grasping power than the common mouse, and is therefore at a disadvantage
in moving about on sloping surfaces. One evidence of this fact is the
character of the tracks made by the animal. Instead of raising its feet
from the substratum and placing them neatly, as does the common mouse
(Figure 5), it tends to shuffle along, dragging its toes and thus
producing on smoked paper such tracks as are seen in Figure 6. From my own
observations I am confident that these figures exaggerate the differences.
My dancers, unless they were greatly excited or moving under conditions of
stress, never dragged their toes as much as is indicated in Figure 6.
However, there can be no doubt that they possess less power of grasping
with their toes than do common mice. The animal is still further
incapacitated for movement on inclined surfaces or narrow places by its
tendency to move in circles and zigzags. The results of my own experiments
indicate that the timidity of the adult is greater than that of the
immature animal when it is placed on a bridge 1 or 2 cm. wide at a
distance of 20 cm. from the ground. Individuals three weeks old showed
less hesitation about trying to creep along such a narrow pathway than did
full-grown dancers three or four months old; and these, in turn, were not
so timid apparently as an individual one year old. But the younger animals
fell off more frequently than did the older ones.

[Illustration: FIGURE 4.--Zoth's photographs of dancers crossing bridges
and climbing rods. Reproduced from _Pfluger's Archiv_, Bd. 86.]

[Illustration: FIGURE 5--Tracks of common mouse Reproduced from Alexander
and Kreidl's figure in _Pfluger's Archiv_, Bd 82]

[Illustration: FIGURE 6--Tracks of dancing mouse Reproduced from Alexander
and Kreidl's figure in _Pfluger's Archiv_ Bd 82]

Additional support for these statements concerning equilibrational ability
is furnished by the observations of Kishi (21 p. 482). He built a wooden
bridge 60 cm. long, 1 cm. wide at one end, and 1/2 cm. at the other, and
supported it at a height of 30 cm. above the ground by posts at the ends.
On this bridge ten dancers were tested. Some attempted to move sidewise,
others began to whirl and fell to the ground; only one of the ten
succeeded in getting all the way across the bridge on the first trial. The
second time he was tested this individual crossed the bridge and found the
post; and the third time he crossed the bridge and climbed down the post
directly. The others did not succeed in descending the post even after
having crossed the bridge safely, but, instead, finally fell to the floor
from awkwardness or exhaustion. On the basis of these and other similar
observations, Kishi says that the dancer possesses a fair degree of
ability to orient and balance itself.

Inasmuch as equilibration occurs similarly in darkness and in daylight,
Zoth thinks that there is neither visual dizziness nor fear of heights.
But it is doubtful whether he is right concerning fear. There is no doubt
in my mind, in view of the way the mice behave when placed on an elevated
surface, that they are timid; but this is due probably to the
uncomfortable and unusual position rather than to perception of their
distance from the ground. That they lack visual dizziness seems fairly
well established.

When rotated in a cyclostat[1] the dancer, unlike the common mouse, does
not exhibit symptoms of dizziness. The following vivid description of the
behavior of both kinds of mice when rotated is given by Alexander and
Kreidl (1 p. 548). I have not verified their observations.

[Footnote 1: An apparatus consisting of a glass cylinder with a mechanism
for turning it steadily and at different speeds about its vertical axis.]

The common mouse at first runs with increasing rapidity, as the speed of
rotation of the cyclostat cylinder is increased, in the direction opposite
to that of the cylinder itself. This continues until the speed of rotation
has increased to about 60 revolutions per minute. As the rotation becomes
still more rapid the mouse begins to crawl along the floor, its body
stretched out and clinging to the floor. At a speed of 250 revolutions per
minute it lies flat on the floor with its limbs extended obliquely to the
movement of rotation, and at times with its back bent against the axis of
the cylinder; in this position it makes but few and feeble efforts to
crawl forward. When the rotation is suddenly stopped, the animal pulls
itself together, remains for some seconds with extended limbs lying on the
floor, and then suddenly falls into convulsions and trembles violently.
After several attacks of this kind, cramps appear and, despite its
resistance, the animal is thrown about, even into the air at times, as if
by an external force. This picture of the position assumed during rapid
rotation, and of cramps after the cessation of rotation (the typical
picture of rotation dizziness), is repeated with great uniformity in the
case of the common mouse. Within fifteen minutes after being returned to
its cage the animal recovers from the effects of its experience. This
description of the symptoms of rotation dizziness in the common mouse
applies equally well to the blinded and the seeing animal.

In sharp contrast with the behavior of the common mouse in the cyclostat
is that of the dancer. As the cylinder begins to rotate the dancer runs
about as usual in circles, zigzags, and figure-eights. As the speed
becomes greater it naturally becomes increasingly difficult for the mouse
to do this, but it shows neither discomfort nor fear, as does the common
mouse. Finally the centrifugal force becomes so great that the animal is
thrown against the wall of the cylinder, where it remains quietly without
taking the oblique position. When the cyclostat is stopped suddenly, it
resumes its dance movements as if nothing unusual had occurred. It
exhibits no signs of dizziness, and apparently lacks the exhaustion which
is manifest in the case of other kinds of mice after several repetitions
of the experiment. The behavior of the blinded dancer is very similar.

If these statements are true, there is no reason to believe that the
dancer is capable of turning or rotation dizziness. If it were, its daily
life would be rendered very uncomfortable thereby, for its whirling would
constantly bring about the condition of dizziness. Apparently, then, the
dancer differs radically from most mammals in that it lacks visual and
rotational dizziness. In the next chapter we shall have to seek for the
structural causes for these facts.

The behavior of the blinded animal is so important in its bearings upon
the facts of orientation and equilibration that it must be considered in
connection with them. Cyon insists that the sense of vision is of great
importance to the dancer in orienting and equilibrating itself. When the
eyes are covered with cotton wads fastened by collodion, this writer
states (9 p. 223) that the mice behave as do pigeons and frogs whose
semicircular canals have been destroyed. They perform violent forced
movements, turn somersaults forward and backward, run up inclines and fall
over the edges, and roll over and over. In a word, they show precisely the
kind of disturbances of behavior which are characteristic of animals whose
semicircular canals are not functioning normally. Cyon, however, observed
that in certain dancers these peculiarities of behavior did not appear
when they were blinded, but that, instead, the animals gave no other
indication of being inconvenienced by the lack of sight than do common
white mice. This matter of individual differences we shall have to
consider more fully later.

No other observer agrees with Cyon in his conclusions concerning vision,
or, for that matter, in his statements concerning the behavior of the
blind dancer. Alexander and Kreidl (1 p. 550) contrast in the following
respects the behavior of the white mouse and that of the dancer when they
are blinded. The white mouse runs less securely and avoids obstacles less
certainly when deprived of vision. The dancer is much disturbed at first
by the shock caused by the removal of its eyes, or in case they are
covered, by the presence of the unusual obstruction. It soon recovers
sufficiently to become active, but it staggers, swerves often from side to
side, and frequently falls over. It moves clumsily and more slowly than
usual. Later these early indications of blindness may wholly disappear,
and only a slightly impaired ability to avoid obstacles remains.

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