POSITION OF WHITE CARDBOARDS FOR A SET OF 150 TESTS
Preference
A l r l r l r
l r l r
B r l r l r l
r l r l
1 r l r l r l r l r l
2 l l r r l r l l r r
3 r r l r l l r l r l
4 l l l r r r l r r l
5 r l r l r l r l r l
6 l l r l r r l r l r
7 r l l l r r r l r l
8 r r l l r l r l r l
9 r r r l l l r l r l
10 l l l l r r r r l r
11 r l r r r l l l r l
12 r l r l r r l l r l
13 r l r l l l r r r l
14 l l l l r r r r l r
15 r l r r r l l l r l
It is to be noted that in the case of each series
of ten tests the white cardboard was on the left five
times and on the right five times. Thus the establishment
of a tendency in favor of one side was avoided.
The irregularity of the changes in position rendered
it impossible for the mouse to depend upon position
in its choice. It is an interesting fact that
the dancer quickly learns to choose correctly by position
if the cardboards are alternately on the left box
and on the right.
The prevalent, although ill-founded, impression that
mice have an exceedingly keen sense of smell might
lead a critic of these experiments to claim that discrimination
in all probability was olfactory rather than visual.
As precautions against this possibility the cardboards
were renewed frequently, so that no odor from the
body of the mouse itself should serve as a guiding
condition, different kinds of cardboard were used
from time to time, and, as a final test, the cardboards
were coated with shellac so that whatever characteristic
odor they may have had for the dancer was disguised
if not totally destroyed. Despite all these precautions
the discrimination of the boxes continued. A still
more conclusive proof that we have to do with brightness
discrimination, and that alone, in these experiments
is furnished by the results of white-black tests
made with an apparatus which was so arranged that light
was transmitted into the two electric-boxes through
a ground glass plate in the end of each box.
No cardboards were used. The illumination of each
box was controlled by changes in the position of the
sources of light. Under these conditions, so
far as could be ascertained by critical examination
of the results, in addition to careful observation
of the behavior of the animals as they made their
choices, there was no other guiding factor than brightness
difference. Nevertheless the mice discriminated
the white from the black perfectly. This renders
unnecessary any discussion of the possibility of discrimination
by the texture or form of the cardboards.
