daily, and not until the twentieth of these series
(200 tests) did he succeed in making ten correct choices
in succession. Immediately after this series of
correct choices, tests with grays No. 10 and No. 15
were begun. In the case of this amount of brightness
difference twenty series failed to reveal discrimination.
The average number of right choices in the series is
slightly in excess of the mistakes, 5.8 as compared
with 4.2.
From the experiments with gray papers we may conclude
that under the conditions of the tests the amount
by which Nendel’s gray No. 10 differs in brightness
from No. 20 is near the threshold of discrimination,
or, in other words, that the difference in the brightness
of the adjacent grays of Figure 16 is scarcely sufficient
to enable the dancer to distinguish them.
GRAY DISCRIMINATION
The Delicacy of Brightness Discrimination
No. 420
GRAYS NOS. 10 GRAYS NOS. 20
AND 20 AND 15
SERIES DATE DATE
NO. 10 NO. 2 NO. 10 NO. 15
(RIGHT) (WRONG) (RIGHT) (WRONG)
1 Jan. 26 5 5 Feb. 6 8 2
2 27 8 2 6 5 5
3 28 6 4 7 9 1
4 28 2 8 7 7 3
5 29 1 9 8 5 5
6 29 6 4 8 6 4
7 30 9 1 9 5 5
8 30 7 3 9 6 4
9 31 6 4 10 8 2
10 31 4 6 10 3 7
11 Feb. 1 7 3 11 4 6
12 1 8 2 11 4 6
13 2 7 3 12 7 3
14 2 8 2 12 7 3
15 3 9 1 13 6 4
16 3 9 1 13 4 6
17 4 6 4 14 4 6
18 4 9 1 14 5 5
19 5 6 4 15 5 5
20 5 10 0 15 8 2
Averages
6.6 3.4 5.8 4.2
This result of the tests with gray papers surprised
me very much at the time of the experiments, for all
my previous observation of the dancer had led me to
believe that it is very sensitive to light. It
was only after a long series of tests with transmitted
light, in what is now to be described as the Weber’s
law apparatus, that I was able to account for the
meager power of discrimination which the mice exhibited
in the gray tests. As it happened, the Weber’s
law experiment contributed quite as importantly to
the solution of our first problem as to that of the
second, for which it was especially planned.
