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.
