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.
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.
