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.
[Illustration: FIGURE 20.--Color discrimination apparatus. _A,_ nest-box;
_B,_ entrance chamber; _R, R,_ red filters; _G,_ green filter; _L, L,_
incandescent lamps in light-box; _S,_ millimeter scale on light-box; _I,_
door between _A_ and _B; O, O,_ doors between alleys and _A_.]
[Illustration: FIGURE 21--Ground plan of color discrimination apparatus.
_E, E_, exits from electric-boxes. _LB_, light-box; _R, G, R_, filter
boxes on carrier; _L_, left electric-box; _R_, right electric-box; _IC_
induction apparatus; _C_, electric cell; _K_, key; _S_, millimeter scale.]
In the tests which are now to be reported, three portions of the spectrum
were used: the red end, the blue-violet end, and a middle region, chiefly
green. The red light was obtained by the use of a filter which was made by
placing two plates of ruby glass in one of the glass boxes, filling the
box with filtered water and then sealing it to prevent evaporation. The
blue-violet was obtained by the use of a filter box which contained a 5
per cent solution of copper ammonium sulphate. The green, which, however,
was not monochromatic, was obtained by the use of a filter box which
contained a saturated solution of nickel nitrate. These three sets of
filters were examined spectroscopically both before the experiments had
been made and after their completion.[1] The red filters, of which I had
two for shifting the lights, transmitted only red light. The blue-violet
filters, two also, at first appeared to transmit only portions of the blue
and violet of the spectrum, but my later examination revealed a trace of
green. It is important to note, however, that the red and the blue-violet
filters were mutually exclusive in the portions of the spectrum which they
transmitted. Of all the filters used the green finally proved the least
satisfactory. I detected some yellow and blue in addition to green in my
first examination, and later I discovered a trace of red. Apparently the
transmitting power of the solutions changed slightly during the course of
the experiments. On this account certain solutions are undesirable for
experiments on color vision, for one must be certain of the constancy of
the condition of stimulation. It is to be understood, of course, that each
of the three filters transmitted, so far as the eye is concerned, only the
color named. I consider the red filter perfectly satisfactory, the blue-
violet very good, and the green poor. Henceforth, in testing color vision
in animals, I shall make use of colored glasses as filters, if it is in
any way possible to obtain or have manufactured blue, green, and yellow
glasses which are as satisfactory as the ruby.
[Footnote 1: A Janssen-Hoffman spectroscope was used.]
The apparatus needs no further description, as its other important
features were identical with those of the reflected light experiment box.
The use of artificial light for the illumination of the electric-boxes
made it necessary to conduct all of the following tests in a dark-room.
The method of experimentation was practically the same as that already
described. A mouse which had been placed in _A_ by the experimenter was
permitted to enter _B_ and thence to return to _A_ by entering one of the
electric-boxes, the red or blue or green one, as the case might be.
Mistakes in choice were punished by an electric shock. One further point
in the method demands description and discussion before the results of the
tests are considered, namely, the manner of regulating and measuring the
brightness of the lights.
Regulating brightness with this apparatus was easy enough; measuring it
accurately was extremely difficult. The experimenter was able to control
the brightness of each of the two colored lights which he was using by
changing the position or the power of the incandescent lamps in the light-
box. The position of a lamp could be changed easily between tests simply
by moving it along toward or away from the electric-box in the slit which
served as a lamp carrier. As the distance from the entrances of the
electric-boxes to the further end of the light-box was 120 cm., a
considerable range or variation in brightness was possible without change
of lamps. Ordinarily it was not necessary to change the power of the
lamps, by replacing one of a given candle power by a higher or lower,
during a series of tests. Both the candle power of the lamps and their
distance from the filters were recorded in the case of each test, but for
the convenience of the reader I have reduced these measurements to candle
meters[1] and report them thus in the descriptions of the experiments.
[Footnote 1: The illuminating power of a standard candle at a distance of
one meter.]
But measuring the actual brightness of the red light or the green light
which was used for a particular series of tests, and the variations in
their brightnesses, was not so simple a matter as might appear from the
statements which have just been made. The influence of the light filters
themselves upon the brightness must be taken into account. The two red
filters were alike in their influence upon the light which entered them,
for they were precisely alike in construction, and the same was true of
the two blue-violet filters. The same kind of ruby glass was placed in
each of the former, and a portion of the same solution of copper ammonium
sulphate was put into each of the filter boxes for the latter. But it is
difficult to say what relation the diminution in brightness caused by a
red filter bore to that caused by a blue-violet or a green filter. My only
means of comparison was my eye, and as subjective measurement was
unsatisfactory for the purposes of the experiment, no attempt was made to
equalize the amounts of brightness reduction caused by the several
filters. So far as the value of the tests themselves, as indications of
the condition of color vision in the dancer is concerned, I have no
apology for this lack of measurement, but I do regret my inability to give
that accurate objective statement of brightness values which would enable
another experimenter with ease and certainty to repeat my tests. The
nearest approach that it is possible for me to make to such an objective
measurement is a statement of the composition and thickness of the filters
and of the candle-meter value of the light when it entered the filter. The
distance from this point to the entrance to the electric-box was 20 cm.
To sum up and state clearly the method of defining the brightness of the
light in the following experiments: the candle-meter value of each light
by which an electric-box was illuminated, as determined by the use of a
Lummer-Brodhun photometer and measurements of the distance of the source
of light from the filter, is given in connection with each of the
experiments. This brightness value less the diminution caused by the
passage of the light through a filter, which has been defined as to
composition and thickness of the layer of solution, gives that degree of
brightness by which the electric-box was illuminated.
Tests of the dancer's ability to discriminate green and blue[1] in the
transmitted light apparatus were made with four animals. An incandescent
lamp marked 16-candle-power was set in each of the light-boxes. These
lamps were then so placed that the green and the blue seemed to be of
equal brightness to three persons who were asked to compare them
carefully. Their candle-meter values in the positions selected were
respectively 18 and 64, as appears from the statement of conditions at the
top of Table 22.
[Footnote 1: Hereafter the light transmitted by the blue-violet filter
will be referred to for convenience as blue.]
TABLE 22
GREEN-BLUE TESTS
Brightnesses Equal for Human Eye
Green 18 candle meters Blue 64 candle meters
SERIES DATE NO. 10 NO. 11
1906 RIGHT WRONG RIGHT WRONG
(GREEN) (BLUE) (GREEN) (BLUE)
A and B[1] April 2 10 10 12 8
1 3 6 4 5 5
2 4 5 5 6 4
3 5 5 5 5 5
4 6 5 5 5 5
5 7 7 3 5 5
6 8 7 3 3 7
7 9 7 3 5 5
8 10 3 7 7 3
9 11 5 5 4 6
10 12 5 5 6 4
[Footnote: A single preference series of twenty tests.]
Numbers 10 and 11 exhibited no preference for either of these colors in
the series of 20 tests which preceded the training tests, and neither of
them gave evidence of ability to discriminate as the result of ten series
of training tests. In this case, again, the behavior of the animals was as
strongly against the inference that they can tell green from blue as are
the records of choices which appear in the table. Granted, that they are
unable to discriminate green from blue when these colors are of about the
same brightness for the human eye, what results when they differ markedly
in brightness? Table 23 furnishes a definite answer to this question.
Numbers 5 and 12 were given eight series of green-blue tests with each
light at 18 candle meters. Little, if any, evidence of discrimination
appeared. Then, on the supposition that the difference was not great
enough for easy discrimination, the blue light was reduced almost to 0,
the green being left at 18. The tests (series 9) immediately indicated
discrimination. For series 10 the green was made 64 candle meters, the
blue 18, and again there was discrimination. These results were so
conclusively indicative of the lack of color vision and the presence of
brightness vision, that there appeared to be no need of continuing the
experiment further.
Accepting provisionally the conclusion that the dancers cannot tell green
from blue except by brightness differences, we may proceed to inquire
whether they can discriminate other colors. Are green and red
distinguishable?
Green-red discrimination now was tested by a method which it was hoped
might from the first prevent dependence upon brightness. The light in the
light-box on the left was so placed that it had a value of 18 candle
meters, that in the light-box on the right so that it had a value of 1800
candle meters. Neither light was moved during the first four series of the
green-red tests which were given to Nos. 151 and 152.
TABLE 23
GREEN-BLUE TESTS
Brightnesses Different for Human Eye
Green 18 candle meters Blue 18 candle meters
No. 5 No. 12
DATE
SERIES 1906 RIGHT WRONG RIGHT WRONG
(GREEN) (BLUE) (GREEN) (BLUE)
1 April 10 6 4 5 5
2 11 5 5 7 3
3 12 6 4 7 3
4 13 4 6 7 3
5 14 7 3 5 5
6 15 4 6 6 4
7 16 6 4 8 2
8 17 5 5 4 6
As it was now evident that the intensity difference was not sufficient to
render discrimination easy, the blue was reduced to 0 and the green left
at 18.
9 17 7 3 8 2
Now the brightnesses were made, green 64, blue 18, just the reverse of
those of series of Table 22.
10 17 8 2 8 2
Each of these series consisted of 20 tests instead of 10. As a result of
the arrangement of the lights just mentioned, the green appeared to me
very much brighter than the red when it was on the right and very much
darker when it was on the left. If this were true for the mouse also, it
is difficult to see how it could successfully depend upon brightness for
guidance in its choices. Such dependence would cause it to choose now the
green, now the red.
The first four series of green-red tests so clearly demonstrated
discrimination, of some sort, that it was at once necessary to alter the
conditions of the experiment. The only criticism of the above method of
excluding brightness discrimination, of which I could think, was that the
red at no time had been brighter than the green. In other words, that
despite a value of 1800 candle meters for the red and only 18 candle
meters for the green, the latter still appeared the brighter to the mouse.
To meet this objection, I made the extreme brightness values 1 and 1800
candle meters in some of the later series, of which the results appear in
Table 24. From day to day different degrees of brightness were used, as is
indicated in the second column of the table. Instead of having first one
color and then the other the brighter, after the fourth series I changed
the position of the lights each time the position of the filters was
changed; hence, the table states a certain brightness value for each color
instead of for each electric-box.
Series 5 to 14 so clearly indicated discrimination, that it seemed
necessary to devise some other means than that of changing the
brightnesses of the colored lights themselves to test the assumption that
the animals were choosing the brighter light. I therefore removed the
light filters so that the colors which had been present as conditions of
discrimination were lacking, and arranged the apparatus so that first one
box, then the other, was illuminated the more brightly. The purpose of
this was to discover whether as the result of their green-red training the
mice had acquired the habit of choosing uniformly either the lighter or
the darker box. One series was given under the conditions of illumination
specified in Table 24 with the result that the brighter box was chosen
eight times in ten by No. 151 and every time by No. 152. Since neither of
these individuals had previously been trained by white-black tests to go
to the white, and since, furthermore, the dancers usually manifest a
slight preference for the lower instead of the higher illumination, this
result may be interpreted as indicative of dependence upon brightness in
the previous color tests. It looks very much indeed as if the green had
been chosen, not because of its greenness, but on account of its
relatively greater brightness.
This test of brightness preference was followed by two series, 16 and 17,
under conditions similar to those of the first four series of the table.
For series 16 the value of the light in the left box was 1 candle meter,
that of the light in the right box 1800 candle meters. Discrimination was
perfect. For series 17 the value for the left remained at 1 candle meter,
but that of the right box was decreased to 0. In this series No. 152 was
entirely at a loss to know which box to choose. Of course this was an
entirely new set of conditions for choice, namely, a colored box, the
green or the red as the case might be, beside a dark box, the one which
was not illuminated. If the mice really had been choosing correctly
because of a habit of avoiding the red or of seeking the green, this
method should bring out the fact, for the red box, since with it the
disagreeable electric shock had always been associated, should be a box to
be avoided. For No. 151 this seemed to be the case.
Series 23 to 27 of Table 24 were given as final and crucial tests of the
relation of brightness discrimination to color discrimination. As it is
not possible to express in a simple formula the conditions of the tests, a
sample series which indicates the brightness of the colors in each of the
twenty tests of a series, and in addition the results given by No. 151 in
the first of these final series, is reproduced in Table 25. For an animal
which had presumably learned perfectly to choose green in preference to
red, the record of 8 mistakes in 20 choices as a result of changes in
relative brightness is rather bad, and it renders doubtful the existence
of color discrimination in any of these experiments. No. 152 showed no
ability whatever to choose the green in the first of the series (series 23
of Table 24) of which that of Table 25 is a sample. His record, 10
mistakes in 20 choices, was even poorer than that of No. 151. That both of
these mice learned to choose fairly accurately in these final tests is
shown by the results of series 24, 25, 26, and 27. I must admit, however,
that these records indicate little ability on the part of the animals to
discriminate colors.
TABLE 24
GREEN-RED TESTS
Brightnesses Extremely Different for Human Eye
Intensities are given in candle meters (c.m.)
NO. 151 NO. 152
SERIES DATE CONDITIONS
RIGHT WRONG RIGHT WRONG
(GREEN) (RED) (GREEN) (RED)
1 April 26 18 c.m. on left
1800 c.m. on right 11 9 7 13
2 27 Same 16 4 16 4
3 28 Same 20 0 17 3
4 29 Same 19 1 19 1
5 30 Green 18 c.m.
Red 18 c.m. 9 1 10 0
6 30 Green 64 c.m.
Red 18 c.m. 9 1 8 2
7 May 1 Green 6 c.m.
Red 1500 c.m. 7 3 9 1
8 1 Green 4 c.m.
Red 1500 c.m. 8 2 7 3
9 2 Both varied from
4 to 1500 c.m. 18 2 18 2
10 3 Green 2 c.m.
Red 1800 c.m. 6 4 7 3
11 3 Same 10 0 10 0
12 4 Same 7 3 8 2
13 4 Same 8 2 6 4
14 5 Green 1 c.m.
Red 1800 c.m. 19 1 19 1
Filters were now removed. An illumination of 15 c.m. was established on
one side and an illumination of 0 on the other side, in order to ascertain
whether the mice would choose the brighter box. This was done to test the
assumption that the green in the previous tests had always appeared
brighter to the mice than did the red, and that in consequence they had
chosen the brighter box instead of the green box.
TABLE 24--CONTINUED
No. 151 No. 152
SERIES DATE CONDITIONS RIGHT WRONG RIGHT WRONG
(GREEN) (RED) (GREEN) (RED)
15 May 5 Brighter 15 c.m. 8[1] 2[2] 10[1] 0[2]
Darker 0 c.m.
16 5 1 c.m. on left
1800 c.m. on right 10 0 10 0
17 5 1 c.m. on left
0 c.m. on right 9 1 4 6
18 5 Green 18 c.m.
Red 18 c.m. 19 1 17 3
19 9 Same 9 1 9 1
20 9 Same 10 0 10 0
21 10 Same 10 0 10 0
22 11 Same 10 0 10 0
23 June 1 Both varied from
1 to 1800 c.m. 12 8 10 10
24 2 Same 18 2 14 6
25 June 3 Both varied from
2 to 1800 c.m. 19 1 17 3
26 4 Same 17 3 17 3
27 5 Same 18 2 18 2
[Footnote 1: Brighter.]
[Footnote 2: Darker.]
These long-continued and varied tests with Nos. 151 and 152 revealed three
facts: that the mice depend chiefly upon brightness differences in visual
discrimination; that they probably have something which corresponds to our
red-green vision, although their color experience may be totally unlike
ours; and that the red end of the spectrum seems much darker to them than
to us, or, in other words, that the least refrangible rays are of lower
stimulating value for them than for us.
TABLE 25
GREEN-RED TESTS
June 1, 1906 No. 151
BRIGHTNESS VALUE IN CANDLE RIGHT WRONG
TEST POSITION METERS (GREEN) (RED)
1 Green on left Green 4, Red 448 Right --
2 Green on right Green 448, Red 4 Right --
3 Green on right Green 4, Red 448 Right --
4 Green on left Green 448, Red 4 Right --
5 Green on left Green 3, Red 1800 -- Wrong
6 Green on right Green 1800, Red 3 -- Wrong
7 Green on right Green 3, Red 1800 -- Wrong
8 Green on left Green 1800, Red 3 Right --
9 Green on right Green 5, Red 34 Right --
10 Green on left Green 34, Red 5 Right --
11 Green on right Green 6, Red 74 Right --
12 Green on left Green 74, Red 6 Right --
13 Green on left Green 4, Red 448 -- Wrong
14 Green on right Green 448, Red 4 Right --
15 Green on right Green 4, Red 448 -- Wrong
16 Green on left Green 448, Red 4 Right --
17 Green on right Green 3, Red 1800 -- Wrong
18 Green on left Green 1800, Red 3 -- Wrong
19 Green on right Green 1800, Red 3 -- Wrong
20 Green on left Green 3, Red 1800 Right --
Totals 12 8
So many of the results of my color experiments have indicated the all-
important role of brightness vision that I have hesitated to interpret any
of them as indicative of true color discrimination. But after I had made
all the variations in brightness by which it seemed reasonable to suppose
that the mouse would be influenced under ordinary conditions, and after I
had introduced all the check tests which seemed worth while, there still
remained so large a proportion of correct choices that I was forced to
admit the influence of the quality as well as of the intensity of the
visual stimulus.
The first of the facts mentioned above, that brightness discrimination is
more important in the life of the mouse than color discrimination, is
attested by almost all of the experiments whose results have been
reported. The second fact, namely, that the dancer possesses something
which for the present we may call red-green vision, also has been proved
in a fairly satisfactory manner by both the reflected and the transmitted
light experiments. I wish now to present, in Table 26, results which
strikingly prove the truth of the statement that red appears darker to the
dancer than to us.
The brightness conditions which appeared to make the discrimination
between green and red most difficult were, so far as my experiments permit
the measurement thereof, green from 1 to 4 candle meters with red from
1200 to 1600. Under these conditions the red appeared extremely bright,
the green very dark, to the human subject.
According to the description of conditions in Table 26, Nos. 2 and 5 were
required to distinguish green from red with the former about 3 candle
meters in brightness and the latter about 1800 candle meters. In the
eighth series of 20 tests, each of these animals made a perfect record. As
it seemed possible that they had learned to go to the darker of the two
boxes instead of to the green box, I arranged the following check test.
The filters were removed, the illumination of one electric-box was made 74
candle meters, that of the other 3, and the changes of the lighter box
from left to right were made at irregular intervals. In February, No. 2
had been trained to go to the black in black-white tests, and at the same
time No. 5 had been trained to go to the white in white-black tests. The
results of these brightness check tests, as they appear in the table,
series 8 _a_, are indeed striking. Number 2 chose the darker box each
time; No. 5 chose it eight times out of ten. Were it not for the fact that
memory tests four weeks after his black-white training had proved that No.
2 had entirely lost the influence of his previous experience (he chose
white nine times out of ten in the memory series), it might reasonably be
urged that this individual chose the darker box because of his experience
in the black-white experiment. And what can be said in explanation of the
choices of No. 5? I can think of no more reasonable way of accounting for
this most unexpected result of the brightness tests than the assumption
that both of these animals had learned to discriminate by brightness
difference instead of by color.
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.
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.
A very definite answer to this question is furnished by observation of the
behavior of the dancers in the tests. Most of them continuously made use
of their eyes, their noses, and their vibrissae. Some individuals used one
form of receptive organ almost exclusively. I frequently noticed that
those individuals which touched and smelled of the labyrinth passages most
carefully gave least evidence of the use of sight. It is safe to say,
then, that under ordinary conditions habit formation in the dancer is
conditioned by the use of sight, touch, and smell, but that these senses
are of extremely different degrees of importance in different individuals.
And further, that, although in the case of some individuals the loss of
sight would not noticeably delay habit formation, in the case of others it
would seriously interfere with the process. When deprived of one sense,
the dancer depends upon its remaining channels of communication with
environment. Indeed there are many reasons for inferring that if deprived
of sight, touch, and smell it would still be able to learn a labyrinth
path; and there are reasonable grounds for the belief that a habit once
formed can be executed in the absence of all special sense data.
Apparently the various receptive organs of the body furnish the dancer
with impressions which serve as guides to action and facilitate habit
formation, although they are not necessary for habit performance.
The reader may wonder why I have not carried out systematic experiments to
determine accurately and quantitatively the part which each sense plays in
the formation of a labyrinth habit instead of basing my inferences upon
incidental observation of the behavior of the dancers. The reason is
simply this: the number and variety of experiments which were suggested by
the several directions in which this investigation developed rendered the
performance of all of them impossible. I have chosen to devote my time to
other lines of experimentation because a very thorough study of the
conditions of habit formation has recently been made by Doctor Watson.[1]
[Footnote 1: Watson, J. B., _Psychological Review_, Monograph Supplement,
Vol. 8, No. 2, 1907.]
What is the role of sight in the dancing mouse? How shall we answer the
question? The evidence which has been obtained in the course of my study
of the animal indicates that brightness vision is fairly acute, that color
vision is poor, that although form is not clearly perceived, movement is
readily perceived. My observations under natural conditions justify the
conclusion that sight is not of very great importance in the daily life of
the dancer, and my observations under experimental conditions strongly
suggest the further conclusion that movement and changes in brightness are
the only visual conditions which to any considerable extent control the
activity of the animal.
CHAPTER XII
EDUCABILITY: METHODS OF LEARNING
Nearly all of the experiments described in earlier chapters have revealed
facts concerning the educability of the dancer. In order to supplement the
knowledge of this subject thus incidentally gained and to discover the
principles of educability, the specially devised experiments whose results
appear in this and succeeding chapters were arranged and carried out with
a large number of mice. In the work on the modifiability of behavior I
have attempted to determine (1) by what methods the dancer is capable of
profiting by experience, (2) the degree of rapidity of learning, (3) the
permanency of changes wrought in behavior, (4) the effect of one kind of
training upon others, (5) the relation of re-training to training, and (6)
the relation of all these matters to age, sex, and individuality.
As it is obvious that knowledge of these subjects is a necessary condition
for the intelligent appreciation of the capacities of an animal, as well
as of the choice of methods by which it may be trained advantageously,
perhaps it is not too much to expect that this investigation of the nature
and conditions of educability in the dancing mouse may give us some new
insight into the significance of certain aspects of human education and
may serve to suggest ways in which we may measure and increase the
efficiency of our educational methods.
Merely for the sake of convenience of description I shall classify the
methods which have been employed as problem methods, labyrinth methods,
and discrimination methods. That these names are not wholly appropriate is
suggested by the fact that discrimination necessarily occurs in connection
with each of them. As problem methods we may designate those tests of
initiative and modifiability which involve the opening of doors by pushing
or pulling them, and the climbing of an inclined ladder. An example of the
labyrinth method has been presented in Chapter XI. The name discrimination
method I have applied to those tests which involve the choice of one of
two visual, tactual, or olfactory conditions. The white-black
discrimination tests, for example, served to reveal the rapidity and
permanency of learning as well as the presence of brightness vision.
In the case of most mammals whose educability has been studied
experimentally, problem methods have proved to be excellent tests of
docility and initiative. The cat, the raccoon, the monkey, in their
attempts to obtain food, learn to pull strings, turn buttons, press
latches, slide bolts, pull plugs, step on levers. The dancer does none of
these things readily. Are we therefore to infer that it is less
intelligent, that it is less docile, than the cat, the raccoon, or the
monkey? Not necessarily, for it is possible that these methods do not suit
the capacity of the animal. As a matter of fact, all of the tests which
are now to be described in their relation to the educability of the dancer
bear witness to the importance of the selection of methods in the light of
the motor equipment and the habits of the animal which is to be tested.
Judged by ordinary standards, on the basis of results which it yields in
problem and labyrinth tests, the dancer is extremely stupid. But that this
conclusion is not justified is apparent when it is judged in the light of
tests which are especially adapted to its peculiarities.
Problems which are easy for other mammals because of their energetic and
persistent efforts to secure food in any way which their motor capacity
makes possible are useless as tests of the dancer's abilities, because it
is not accustomed to obtain its food as the result of strenuous and varied
activities. There are problems and problems; a condition or situation
which presents a problem to one organism may utterly lack interest for an
organism of different structure and behavior. What is a problem test in
the case of the cat or even of the common mouse, is not necessarily a
problem for the dancer. Similarly, in connection with the labyrinth
method, it is clear that the value of the test depends upon the desire of
the organism to escape from the maze. The cat, the rat, the tortoise do
their best to escape; the dancer is indifferent. Clearly, then, methods of
training should be chosen on the basis of a knowledge of the
characteristics of the animal whose educability is to be investigated.
The simplest possible test of the intelligence of the dancer which I could
devise was the following. Beside the cage in which the mice were kept I
placed a wooden box 26 cm. long, 23 cm. wide, and 12 cm. deep. Neither
this box nor the cage was covered, for the animals did not attempt to
climb out. As a way of passing from one of these boxes to the other I
arranged a ladder made of wire fly-screen netting. This ladder was about 8
cm. broad and it extended from the middle of one side of the wooden box
upward at an angle of about 30° to the edge of the box and then descended
at the same angle into the cage.
A dancer when taken from the nest-box and placed in the wooden box could
return to its cage and thus find warmth, food, and company by climbing the
ladder. It was my aim to determine, by means of this apparatus, whether
the dancers can learn such a simple way of escape and whether they learn
by watching one another. As it turned out, a third value belonged to the
tests, in that they were used also to test the influence of putting the
mice through the act.
In the first experiment three dancers, Nos. 1000, 2, and 6, were together
placed in the wooden box. At the end of 15 minutes not one of them had
succeeded in returning to the cage. They were then driven to the bottom of
the ladder and started upward by the experimenter; with this assistance
all escaped to the nest-box. At the expiration of 5 minutes they were
again placed in the wooden box, whence the chilly temperature (about 60°
F.) and the lack of food made them eager to return to their cage. No
attempt to climb up the ladder was made by any of them within 15 minutes,
so the experimenter directed them to the ladder and started them upward as
in the first test. This completed the experiment for the day. The
following day two tests were given in the same way. In the second of these
tests, that is, on its fourth trial, No. 1000 climbed over of his own
initiative in 5 minutes. The others had to be assisted as formerly. On the
third day No. 1000 found his way back to the nest-box quickly and fairly
directly, but neither No. 2 or No. 6 climbed of its own initiative in the
first test. When their movements were restricted to the region of the box
about the base of the ladder, both of them returned to the cage quickly.
And on the second test of the third day all the mice climbed the ladder
directly.
In Table 35 I have given the time required for escape in the case of 40
tests which were given to these 3 individuals at the rate of 2 tests per
day.
When the time exceeded 15 minutes the mice were helped out by the
experimenter; a record of 15 minutes, therefore, indicates failure.
Naturally enough the motives for escape were not sufficiently strong or
constant to bring about the most rapid learning of which the dancer is
capable. Sometimes they would remain in the wooden box washing themselves
for several minutes before attempting to find a way of escape. On this
account I made it a rule to begin the time record with the appearance of
active running about. The daily average time of escape as indicated in the
table does not decrease regularly and rapidly. On the fourth day, which
was the first on which all three of the dancers returned to the cage by
way of the ladder of their own initiative in both tests, the average is
214 seconds. In contrast with this, on the twentieth day the time was only
5 seconds. It is quite evident that the dancers had learned to climb the
ladder.
At the end of the twentieth day the experiment was discontinued with Nos.
2 and 6, and after two weeks they were given memory tests, which showed
that they remembered perfectly the ladder-climbing act, for when placed in
the wooden box, with Nos. 4 and 5 as controls, they returned to the cage
by way of the ladder immediately and directly.
TABLE 35
LADDER CLIMBING TEST
Time in Minutes and Seconds
No. of Date No. 1000 No. 2 No. 6 Average Daily Av.
Exp. 1905 For All For All
1 Nov. 14 15' 15' 15' -- --
2 15' 15' 15' -- --
3 15 15' 15' 15' -- --
4 300" 15' 15' -- --
5 16 480" 15' 15' -- --
6 180" 300" 420" 300" 300"
7 17 450" 240" 540" 410"
8 20" 15" 18" 18" 214"
9 18 90" 180" 135" 135"
10 135" 105" 165" 135" 135"
11 19 480" 240" 330" 350"
12 30" 120" 90" 80" 143"
13 20 360" 75" 120" 185"
14 5" 6" 8" 6" 95"
15 21 105" 450" 120" 192"
16 8" 80" 20" 54" 123"
17 22 255" 300" 180" 245"
18 10" 30" 270" 103" 174"
19 23 300" 660" 450" 470"
20 90" 120" 150" 120" 295"
21 24 240" 125" 225" 197"
22 4" 6" 168" 59" 128"
23 Nov. 25 305" 85" 130" 173"
24 5" 6" 118" 43" 108"
25 26 3" 8" 44" 18"
26 19" 1" 176" 98" 58"
27 27 150" 79" 269" 166"
28 26" 3" 31" 20" 93"
29 28 214" 18" 267" 166"
30 40" 3" 4" 16" 91"
31 29 130" 45" 250" 142"
32 12" 3" 25" 13" 77"
33 Dec. 2 61" 35" 44" 47"
34 50" 5" 24" 26" 36"
35 3 66" 18" 2" 29"
36 8" 5" 10" 8" 19"
37 4 9" 4" 3" 5"
38 10" 5" 6" 7" 6"
39 5 5" 3" 5" 4"
40 10" 4" 3" 6" 5"
One of the most interesting and important features of the behavior of the
dancer in the ladder experiment was a halt at a certain point on the
ladder. It occurred just at the edge of the wooden box at the point where
the ladder took a horizontal position, and led over into the cage. Every
individual from the first test to the last made this halt. Although from
the point of view of the experimenter the act was valueless, it may have
originated as an attempt to find a way to escape from the uncomfortable
position in which the animal found itself on reaching the top of the
ladder. Its persistence after a way of escape had been found is an
indication of the nature of habit. Day after day the halt became shorter
until finally it was little more than a pause and a turn of the head
toward one side of the ladder. I think we may say that in this act we have
evidence of the persistence of a particular resolution of physiological
states which is neither advantageous nor disadvantageous to the organism.
Had the act resulted in any gain, it would have become more marked and
elaborate; had it resulted in injury or discomfort, it would have
disappeared entirely. I have observed the same kind of behavior in the
frog and in other animals. What the animal begins to do it persists in
unless the act is positively harmful or conflicts with some beneficial
activity. The only explanation of certain features of behavior is to be
found in the conditions of their original occurrence. They persist by
sheer force of conservatism. They have value only in the light of the
circumstances under which they first appeared. Although this is merely a
fact of habit formation, it suggests that many of the problems which have
puzzled students of behavior for ages may be solved by a study of the
history of activity.
That there are marked individual differences in intelligence in the
dancing mice is apparent from the results of the ladder-climbing
experiment. No. 1000 learned to climb quickly, and largely by his own
initiative; Nos. 2 and 6, on the contrary, learned only by reason of
tuition (being put through the required act by the experimenter). It
occurred to me that this experiment, since it was difficult for some
individuals and easy for others, might be used to advantage as a test of
imitation. If a dancer which knows how to escape to the cage by way of the
ladder be placed in the wooden box with one which, despite abundant
opportunity, has proved unable to form the habit on his own initiative,
will the latter profit by the activity of the former and thus learn the
method of escape?
On November 20, Nos. 4 and 5 were placed in the wooden box and left there
for half an hour. As they had failed to escape at the end of this
interval, they were taken out of the box by the experimenter and returned
to the nest-box. November 21 and 22 this test of their ability to learn to
climb the ladder was repeated with the same result. On November 23 they
were placed in the box with the three mice which had previously been
trained to climb the ladder. The latter escaped at once. Apparently the
attention of Nos. 4 and 5 was drawn to the ladder by the disappearance of
their companions, for they approached its foot and No. 5 climbed up a
short distance. Neither succeeded in escaping, however, and they made no
further efforts that day. On the 24th, and daily thereafter until the
29th, these two dancers were placed in the box for half an hour, with
negative results. At the end of the half hour on the 29th, Nos. 2 and 6
were placed in the box and permitted to go back and forth from one box to
the other repeatedly within sight of Nos. 4 and 5. The latter made no
attempts to follow them, although at times they seemed to be watching
their movements as they ascended the ladder.
To render the results of this test of imitation still more conclusive No.
5 was given further opportunity to learn from No. 1000. Beginning December
2, the following method of experimentation was employed with these two
individuals. They were placed in the wooden box together. No. 1000 usually
climbed out almost immediately. Sometimes No. 5 apparently saw him
disappear up the ladder; sometimes she paid no attention whatever either
to the presence or absence of her companion. After he had been in the
nest-box for a few seconds, No. 1000 was returned to the wooden box by the
experimenter and again permitted to climb out for the benefit of No. 5.
This mode of procedure was kept up until No. 1000 had made from three to
ten trips. No. 5 was left in the box for half an hour each day. This test
was repeated on 18 days within a period of 3 weeks. No. 5 showed no signs
of an imitative tendency, and she did not learn to climb the ladder.
To this evidence of a lack of an imitative tendency in the dancer I may
here add the results of my observations in other experiments. In the
discrimination tests and in the labyrinth tests I purposely so arranged
conditions, in certain instances, that one individual should have an
opportunity to imitate another. In no case did this occur. Seldom indeed
did the animals so much as follow one another with any considerable degree
of persistence. They did not profit by one another's acts.
Excellent evidence in support of this conclusion was furnished by the
behavior of the mice in the discrimination experiments. Some individuals
learned to pull as well as to push the swinging wire doors of the
apparatus and were thus enabled to pass through the doorways in either
direction; other individuals learned only to pass through in the direction
in which the doors could be pushed open. Naturally I was interested to
discover whether those which knew only the trick of opening the doors by
pushing would learn to pull the doors or would be stimulated to try by
seeing other individuals do so. At first I arranged special tests of
imitation in the discrimination box; later I observed the influence of the
behavior of one mouse upon that of its companion in connection with visual
discrimination experiments. This was made possible by the fact that
usually a pair of individuals was placed in the discrimination box and the
tests given alternately to the male and to the female. Both individuals
had the freedom of the nest-box and each frequently saw the other pass
through the doorway between the nest-box, _A_, and the entrance chamber,
_B_ (Figure 14), either from _A_ to _B_ by pushing the swing door or from
_B_ to _A_ by pulling the door.
Although abundant opportunity for imitation in connection with the opening
of the doors in the discrimination box was given to twenty-five
individuals, I obtained no evidence of ability to learn by imitation. The
dancers did not watch the acts which were performed by their companions,
and in most instances they did not attempt to follow a mate from nest-box
to entrance chamber.
These problem tests, simple as they are, have revealed two important facts
concerning the educability of the dancer. First, that it does not learn by
imitation to any considerable extent, and, second, that it is aided by
being put through an act. Our general conclusion from the results of the
experiments which have been described in this chapter, if any general
conclusion is to be drawn thus prematurely, must be that the dancing mouse
in its methods of learning differs markedly from other mice and from rats.
CHAPTER XIII
HABIT FORMATION: THE LABYRINTH HABIT
The problem method, of which the ladder and door-opening tests of the
preceding chapter are examples, has yielded interesting results concerning
the individual initiative, ingenuity, motor ability, and ways of learning
of the dancer; but it has not furnished us with accurate measurements of
the rapidity of learning or of the permanency of the effects of training.
In this chapter I shall therefore present the results of labyrinth
experiments which were planned as means of measuring the intelligence of
the dancer.
The four labyrinths which have been used in the investigation may be
designated as _A, B, C,_ and _D_. They differ from one another in the
character of their errors, as well as in the number of wrong choices of a
path which the animal might make on its way from entrance to exit. In the
use of the labyrinth method, as in the case of the discrimination method
of earlier chapters, the steps by which a satisfactory form of labyrinth
for testing the dancer was discovered are quite as interesting and
important for those who have an intelligent appreciation of the problems
and methods of animal psychology as are the particular results which were
obtained. For this reason, I shall describe the various forms of labyrinth
in the order in which they were used, whether they proved satisfactory or
not. At the outset of this part of my investigation, it was my purpose to
compare directly the capacity for habit formation in the dancer with that
of the common mouse. This proved impracticable because the same labyrinth
is not suited to the motor tendencies of both kinds of mice.
[Illustration: FIGURE 25.--Labyrinth A. _I_. entrance; _O_, exit; 1, 2, 3,
4, blind alleys.]
The first of the four labyrinths, A, appears in ground plan in Figure 25.
It was constructed of wood, as were the other labyrinths also, and
measured 60 cm. in length and width, and 10 cm. in depth. The outside
alleys were 5 cm. wide. In the figure, _I_ marks the starting point or
entrance to the maze, and _O_ the exit through which the mouse was
permitted to pass into its nest-box. Any turn in the wrong direction which
the animal made in its progress from entrance to exit was recorded as an
error. The four errors, exclusive of the mistake of turning back, which
were possible in this labyrinth, are indicated in the figure by the
numerals 1, 2, 3, and 4. By retracing its steps a mouse might repeat any
one or all of these errors, and add to them the error of turning back.
In the experiments a mouse was permitted to enter the maze from a small
box which had been placed by the experimenter at _I_, and an accurate
record was kept of the number of errors which it made in finding its way
from entrance to exit, and of the time occupied. Each of five dancers was
given 31 tests in this labyrinth. The number of tests per day varied, as
is indicated in Table 36, from 1 to 4. The results of the tests, so far as
errors and times are in question, appear in the table. _T_ at the head of
a column is an abbreviation for time, _E_ for errors.
The dancers did not learn to escape from this labyrinth easily and
quickly. In fact, the average time of the thirty-first test (198") is
considerably longer than that of the first (130"). The number of errors
decreased, it is true, but even for the last test it was 6.6 as compared
with only a little more than twice that number for the first test. The
last column of the table furnishes convincing proof of the truth of the
statement that the animals did not acquire a perfect labyrinth-A habit.
Was this due to inability to learn so complex a path, or to the fact that
the method is not adapted to their nature? Observation of the behavior of
the mice in the experiments enables me to say with certainty that there
was no motive for escape sufficiently strong to establish a habit of
following the direct path. Often, especially after a few experiences in
the maze, a dancer would wander back and forth in the alleys and central
courts, dancing much of the time and apparently exploring its surroundings
instead of persistently trying to escape. This behavior, and the time and
error results of the accompanying table, lead me to conclude that the
labyrinth method, as it has been employed in the study of the intelligence
of several other mammals, is not a satisfactory test of the ability of the
dancer to profit by experience. That the fault is not in the labyrinth
itself is proved by the results which I obtained with common mice.
TABLE 36
RESULTS OF LABYRINTH A TESTS WITH DANCERS
AVERAGE
TEST DATE No. 1000 No. 2 No. 6 No. 4 No. 5 FOR ALL
1905
T E T E T E T E T E T E
1 Nov 23 130" 14 100" 8 170" 13 60" 6 190" 26 130" 13.4
2 24 140 19 78 7 60 8 149 6 211 25 128 13.0
3 25 392 31 87 1 98 5 185 13 120 9 176 11.8
4 26 448 38 38 3 47 2 50 3 121 12 141 11.3
5 27 142 8 21 2 27 3 27 2 17 1 47 3.2
6 28 45 2 61 7 63 5 102 8 33 4 61 5.2
7 29 303 17 64 7 36 3 42 2 57 4 100 6.6
8 30 222 15 26 2 37 5 42 3 7 0 67 5.0
9 Dec 1 185 9 36 5 48 3 63 3 94 8 85 5.6
10 2 52 2 71 4 19 0 196 5 95 11 87 4.4
11 3 180 8 32 2 107 4 52 3 38 4 82 4.2
12 4 310 10 133 11 65 3 242 6 125 6 175 7.2
13 4 153 9 335 55 130 10 195 15 154 18 193 21.4
14 5 330 7 69 2 42 2 201 6 130 10 154 5.4
15 5 287 7 34 4 61 4 136 7 25 2 109 4.8
16 5 455 15 65 4 25 0 110 8 160 15 183 8.4
17 6 120 15 280 9 33 0 168 4 39 2 128 6.0
18 6 120 4 164 10 81 4 101 5 85 4 110 5.4
19 6 132 12 78 7 110 6 40 2 151 12 102 7.8
20 7 258 10 223 16 33 1 92 5 37 1 129 6.6
21 7 110 7 23 3 44 4 20 4 305 23 100 8.2
22 7 100 4 60 8 167 15 44 7 58 4 86 7.6
23 8 43 1 179 7 356 6 34 3 65 3 135 4.0
24 8 92 5 56 5 42 3 17 1 23 1 46 3.0
25 9 85 5 114 3 62 3 129 8 31 0 84 3.8
26 9 30 2 36 4 109 15 12 1 34 2 44 4.8
27 9 69 5 40 4 85 6 36 3 16 1 49 3.8
28 10 169 7 80 3 28 0 142 5 35 2 89 3.4
29 10 155 5 266 8 91 5 27 0 37 2 115 4.0
30 10 29 1 25 2 124 14 83 6 111 12 74 7.0
31 10 465 6 208 8 95 3 65 3 159 13 198 6.6
On the basis of two tests per day, two common mice, a white one and a gray
one, quickly learned to escape from labyrinth _A_ by the shortest path.
The time of escape for the gray individual (Table 37) decreased from 180"
in the first test to 21" in the tenth, and the number of errors from 6 to
1. Similarly in the case of the white individual, the time decreased from
122" to 8", and the errors from 5 to 1. A fraction of the number of tests
to which the dancer had been subjected sufficed to establish a habit of
escape in the common mouse. It is evident, therefore, that the dancer
differs radically from the common mouse in its behavior in a maze, and it
is also clear that the labyrinth method, if it is to be used to advantage,
must be adapted to the motor tendencies of the animal which is to be
tested.
TABLE 37
RESULTS OF LABYRINTH A TESTS WITH COMMON MICE
GREY MOUSE WHITE MOUSE
TEST T E T E
1 180" 6 122" 5
2 26 2 80 6
3 37 1 56 4
4 18 0 27 1
5 68 2 33 2
6 10 1 19 1
7 11 1 17 1
8 13 1 17 1
9 10 0 8 1
10 21 1 8 1
The behavior of the dancer made obvious two defects in labyrinth A. Its
passages are so large that the mouse is constantly tempted to dance, and
it lacks the basis for a strong and constant motive of escape by the
direct path. To obviate these shortcomings labyrinth B was constructed, as
is shown in Figures 23 and 24, with very narrow passages, and a floor
which was covered with the wires of an interrupted electric circuit so
that errors might be punished. The length of this labyrinth was 52 cm. and
the passages were 2.5 cm. wide and 10 cm. deep. Dancing in these narrow
alleys was practically impossible, for the mice could barely turn around
in them. In the case of all except the common mice and two dancers, a
depth of 10 cm. was sufficient to keep the animals in the maze without the
use of a cover.
As an account of the behavior of the dancer in labyrinth B has already
been given in Chapter XI, I may now state the general results of the
experiments. In all, thirty individuals were trained in this labyrinth.
Each individual was given tests at the rate of one per minute until it had
succeeded in following the correct path five times in succession. The weak
electric shock, which was given as a punishment for mistakes, provided an
activity-impelling motive for escape to the nest-box.
An idea of the extreme individual difference in the rapidity with which
the labyrinth-B path was learned by these dancers may be obtained by an
examination of Table 38, from which it appears that the smallest number of
training tests necessary for a successful or errorless trip through the
maze was one and the largest number fourteen. It is to be remembered that
each mouse was given an opportunity to pass through the labyrinth once
without punishment for errors, and thus to discover, before the training
tests were begun, that a way of escape existed. This first test we may
designate as the preliminary trial. Table 38 further indicates that the
females acquired the labyrinth habit more quickly than did the males.
TABLE 38
RESULTS OF LABYRINTH-B EXPERIMENTS, WITH TWENTY DANCERS
MALES FEMALES
NO. OF NO. OF FIRST NO. OF LAST OF NO. OF NO. OF FIRST NO. OF LAST OF
MOUSE CORRECT FIVE CORRECT MOUSE CORRECT FIVE CORRECT
TEST TESTS TEST TESTS
76 8 14 75 4 15
78 5 20 77 7 11
86 13 22 87 12 22
58 2 14 49 1 5
50 6 23 57 3 20
60 13 37 59 14 28
410 6 20 415 4 13
220 4 8 225 6 18
212 3 7 211 6 10
214 10 28 213 5 14
AV. 7.0 19.3 AV. 6.2 15.6
A graphic representation of certain of the important features of the
process of formation of the labyrinth-B habit is furnished by Figure 26 in
which the solid line is the curve of learning for the ten males of Table
38, and the broken line for the ten females. These two curves were plotted
from the number of errors made in the preliminary trial (P in the figure)
and in each of the subsequent tests up to the sixteenth. In the case of
both the males and the females, for example, the average number of errors
in the preliminary trial was 11.3, as is indicated by the fact that the
curves start at a point whose value is given in the left margin as 11.3.
In the second training test the number of errors fell to 3.3 for the males
and 2.7 for the females. The number of the test is to be found on the base
line; the number of errors in the left margin. If these two curves of
learning were carried to their completion, that for the males would end
with the thirty-seventh test, and that for the females with the twenty-
eighth.
[Illustration: FIGURE 26.--Curves of habit formation, plotted from the
data of labyrinth-B tests with ten males and ten females. The figures in
the left margin indicate the number of errors; those below the base line
the number of the test. _P_ designates the preliminary test. Males
____[solid line]; Females ----[broken line].]
Time records are not reported for these and subsequent labyrinth tests
because they proved to be almost valueless as measures of the rapidity of
habit formation. At any point in its progress through a labyrinth, the
dancer may suddenly stop to wash its face, look about or otherwise examine
its surroundings; if a shock be given to hurry it along it may be
surprised into an error. It is my experience, and this is true of other
animals as well as of the dancing mouse, that a long trip, as measured in
time units, does not necessarily indicate the lack of ability to follow
the labyrinth path correctly and rapidly. Hence, whenever it is possible
(and the experimenter can always plan his tests so that it shall be
possible), the number of errors should be given first importance and the
time of the test second place. I have presented in Table 38 the number of
the first correct test, and the number of the last of five successive
correct tests. Space cannot be spared for records of the errors made in
the several tests by each individual.
In general, labyrinth B proved very satisfactory as a means of testing the
ability of the dancer to learn a simple path. The narrow passages
effectively prevented dancing, and the introduction of the electric shock
as a punishment for mistakes developed a motive for escape which was
uniform, constant, and so strong that the animals clearly did their best
to escape from the labyrinth quickly and without errors. This maze was so
simple that it did not tend to discourage them as did the one which is
next to be described. It must be admitted, however, that, though labyrinth
B is perfectly satisfactory as a test of the dancer's ability to learn to
follow a simple path, it is not an ideal means of measuring the rapidity
of habit formation. This is due to the fact that the preliminary trial and
the first training test play extremely different roles in the case of
different individuals. A dancer which happens to follow the correct path
from entrance to exit in the preliminary trial may continue to do so, with
only an occasional error, during several of the early training tests, and
it may therefore fail for a considerable time to discover that there are
errors which should be avoided. The learning process is delayed by its
accidental success. On the other hand, an individual which happens to make
many mistakes to begin with immediately attempts to avoid the points in
the maze at which it receives the electric shock. I was led to conclude,
as a result of the labyrinth-B experiments, that the path was too easy,
and that a more complex labyrinth would, in all probability, furnish a
more satisfactory means of measuring the rapidity of habit formation.
[Illustration: FIGURE 27--A record sheet, showing the plan of labyrinth C
(as made on the sheet by means of a rubber stamp) on which the
experimenter recorded the path followed by the mouse. This sample sheet
presents the path records for the first, fifth, tenth, and eleventh tests
of No. 2 in labyrinth C. 1, 2, 3, 4, 5 designate the several errors of the
labyrinth.]
On the basis of the supposition that a maze whose path was so complex that
the animal would not be likely to follow it correctly in the early trials
would be more to the purpose than either A or B, labyrinth C was devised.
As is shown in the plan of this maze, Figure 27, five mistakes in choice
of path were possible on the forward trip. These errors, as a rule, were
more difficult for the dancers to avoid than those of labyrinths A and B.
Those which are designated by the numerals 2, 3, and 4 were especially
difficult. Error 4 was much more troublesome for left whirlers than for
right whirlers because, after turning around abruptly at the entrance to
the blind alley, the former type of dancer almost always followed the side
wall of the maze so far that it missed the correct path. Undoubtedly the
various errors are not of the same value for different individuals; but it
would be extremely difficult, if not impossible, to devise a maze which
should be equally difficult for several normal individuals.
In order that records of the path followed by a mouse in test after test
might be kept with ease and accuracy by the experimenter, the plan of this
labyrinth, and also that of labyrinth D, were cast in rubber. The outlines
of labyrinths C and D which appear in Figures 27 and 28 respectively were
made with the rubber stamps which were thus obtained. Figure 27 is the
reproduction of a record sheet which presents the results of the first,
the fifth, the tenth, and the eleventh tests of No. 2 in labyrinth C. The
path followed by this individual in the first test was far too complex to
be traced accurately on the record sheet. The record therefore represents
merely the number of errors which was made in each region of the maze. For
the fifth test, and again for the tenth and the eleventh, the path was
recorded accurately. This simple device for making record blanks which can
readily be filled in at the time of the experiment should recommend itself
to all students of animal behavior.
In labyrinth C ten pairs of dancers were given continuous training tests
at the rate of one test per minute until they were able to follow the
direct path correctly. Because of the difficulty in learning this maze
perfectly, it was not demanded of the mice that they should follow the
path correctly several times in succession, but instead the training was
terminated after the first successful trip.
TABLE 39
RESULTS OF LABYRINTH-C EXPERIMENTS, WITH TWENTY DANCERS
MALES FEMALES
NO. OF NO. OF FIRST NO. OF NO. OF FIRST
MOUSE CORRECT TEST MOUSE CORRECT TEST
2 11 29 15
30 33 49 34
50 49 57 15
52 22 59 15
58 16 215 10
60 17 415 10
76 3 75 8
78 6 77 11
86 5 87 9
88 25 85 11
AV. 18.7 AV. 13.8
The results of the experiments with this labyrinth as they are presented
in Table 39 indicate that its path is considerably more difficult for the
dancer to learn than that of labyrinth B, that the females learn more
quickly than the males, and finally, that individual differences are just
as marked as they were in the case of the simpler forms of labyrinth. It
therefore appears that increasing the complexity of a labyrinth does not,
as I had supposed it might, diminish the variability of the results.
Certain of the individual differences which appear in Table 39 are due,
however, to the fact that in some cases training in labyrinth B had
preceded training in labyrinth C, whereas in the other cases C was the
first labyrinth in which the animals were tested. But even this does not
serve to account for the wide divergence of the results given by No. 2 and
No. 50, for the latter had been trained in B previous to his training in
C, and the former had not been so trained. Yet, despite the advantage
which previous labyrinth experience gave No. 50, he did not learn the path
of C as well in fifty tests as No. 2 did in eleven. The facts concerning
the value of training in one form of labyrinth for the learning of
another, as they were revealed by these experiments, may more fittingly be
discussed in a later chapter in connection with the facts of memory and
re-learning.
[Illustration: FIGURE 28.--Plan of Labyrinth _D_, as reproduced from a
print made with a rubber stamp. _I_, entrance; _O_, exit; numerals 1 to
13, errors.]
Labyrinth C is a type of maze which might properly be described as
irregular, since the several possible errors are extremely different in
nature. In view of the results which this labyrinth yielded, it seemed
important that the dancer be tested in a perfectly regular maze of the
labyrinth-D type. The plan which I designed as a regular labyrinth has
been reproduced, from a rubber stamp print, in Figure 28. As is true also
of the mazes previously described, it provides four kinds of possible
mistakes: namely, by turning to the left (errors 1, 5, 9, and 13), by
turning to the right (errors 3, 7, and 11), by moving straight ahead
(errors 2, 4, 6, 8, 10, and 12), and by turning back and retracing the
path just followed. The formula for the correct path of _D_ is simple in
the extreme, in spite of the large number of mistakes which are possible,
for it is merely "a turn to the right at the entrance, to the left at the
first doorway, and thereafter alternately to the right and to the left
until the exit is reached." This concise description would enable a man to
find his way out of such a maze with ease. Labyrinth D had been
constructed with an exit at 10 so that it might be used as a nine-error
maze if the experimenter saw fit, or as a thirteen-error maze by the
closing of the opening at 10. In the experiments which are now to be
described only the latter form was used.
Can the dancer learn a regular labyrinth path more quickly than an
irregular one? Again, I may give only a brief statement of results. Each
of the twenty dancers, of Table 40, which were trained in labyrinth D had
previously been given opportunity to learn the path of C, and most of them
had been trained also in labyrinth B. All of them learned this regular
path with surprising rapidity. The numerical results of the tests with
labyrinths B, C, and D, as well as the behavior of the mice in these
several mazes, prove conclusively that the nature of the errors is far
more important than their number. Labyrinth D with its thirteen chances of
error on the forward trip was not nearly as difficult for the dancer to
learn to escape from as labyrinth C with its five errors. That the
facility with which the twenty individuals whose records are given in
Table 40 learned the path of D was not due to their previous labyrinth
experience rather than to the regularity of the maze is proved by the
results which I obtained by testing in D individuals which were new to
labyrinth experiments. Even in this case, the number of tests necessary
for a successful trip was seldom greater than ten. If further evidence of
the ease with which a regular labyrinth path may be followed by the dancer
were desired, it might be obtained by observation of the behavior of an
individual in labyrinths C and D. In the former, even after it has learned
the path perfectly, the mouse hesitates at the doorways from time to time
as if uncertain whether to turn to one side or go forward; in the latter
there is seldom any hesitation at the turning points. The irregular
labyrinth is followed carefully, as by choice of the path from point to
point; the regular labyrinth is followed in machine fashion,--once
started, the animal dashes through it.
TABLE 40
RESULTS OF LABYRINTH-D EXPERIMENTS, WITH TWENTY DANCERS
MALES FEMALES
NO. OF NO. OF FIRST NO. OF LAST OF NO. OF NO. OF FIRST NO. OF LAST OF
MOUSE CORRECT TWO CORRECT MOUSE CORRECT TWO CORRECT
TEST TESTS TEST TESTS
2 3 7 29 10 11
58 7 10 49 7 8
30 9 10 57 3 6
60 10 14 215 6 10
402 10 11 415 7 8
76 4 7 75 4 13
78 4 5 77 11 12
86 3 9 87 4 9
88 4 8 85 3 4
90 7 8 83 4 7
Av. 6.1 8.9 Av. 5.9 8.8
From the results of these labyrinth experiments with dancers I am led to
conclude that a standard maze for testing the modifiability of behavior of
different kinds of animals should be constructed in conformity with the
following suggestions. Errors by turning to the right, to the left, and by
moving forward should occur with equal frequency, and in such order that
no particular kind of error occurs repeatedly in succession. If we should
designate these three types of mistake by the letters _r, l_, and _s_
respectively, the error series of labyrinth C would read _l-l-r-s-l_. It
therefore violates the rule of construction which I have just formulated.
In the case of labyrinth D the series would read _l-s-r-s-l-s-r-s-l-s-r-s-
l_. This also fails to conform with the requirement, for there are three
errors of the first type, four of the second, and six of the third. Again,
in a standard maze, the blind alleys should all be of the same length, and
care should be taken to provide a sufficiently strong and uniform motive
for escape. In the case of one animal the desire to escape from
confinement may prove a satisfactory motive; in the case of another, the
desire for food may conveniently supplement the dislike of confinement;
and in still other cases it may appear that some form of punishment for
errors is the only satisfactory basis of a motive for escape. Readers of
this account of the behavior of the dancing mouse must not infer from my
experimental results that the electric shock as a means of forcing
discrimination will prove satisfactory in work with other animals or even
with all other mammals. As a matter of fact it has already been proved by
Doctor G. van T. Hamilton that the use of an electric shock may so
intimidate a dog that experimentation is rendered difficult and of little
value. And finally, in connection with this discussion of a standard
Labyrinth, I wish to emphasize the importance of so recording the results
of experiments that they may be interpreted in terms of an animal's
tendency to turn to the right or to the left. My work with the dancer has
clearly shown that the avoidance of a particular error may be extremely
difficult for left whirlers and very easy for right whirlers.