It is now necessary to justify the interpretation
of these results as evidence of brightness discrimination
by proving that all other conditions for choice except
brightness difference may be excluded without interfering
with the animal’s ability to select the right
box. We shall consider in order the possibility
of discrimination by position, by odor, and by texture
and form of the cardboards.
The tendency which the dancer has in common with many,
if not all, animals to perform the same movement or
follow the same path under uniform conditions is an
important source of error in many habit-formation
experiments. This tendency is evident even from
casual observation of the behavior of the dancer.
The ease with which the habit of choosing the box
on the left or the box on the right is formed in comparison
with that of choosing the white box or the black box
is strikingly shown by the following experiment.
Five mice were given one series of ten trials each
in the discrimination box of Figure 14 without the
presence of cardboards or of other means of visual
discrimination. The electric shock was given
whenever the box on the left was entered. Thus
without other guidance than that of direction, for
the boxes themselves were interchanged in position,
and, as was proved by additional tests, the animals
were utterly unable to tell one from the other, the
mouse was required to choose the box on its right.
Only one of the five animals went to the box on the
left after once experiencing the electric shock.
The results of the series are given in Table 11.
TABLE 11
CHOICE BY POSITION
Choices
of Choices of
Box
on Right Box on Left
First mouse 9
1
Second mouse 8
2
Third mouse 9
1
Fourth mouse 9
1
Fifth mouse 9
1
This conclusively proves that the habit of turning
in a certain direction or of choosing by position
can be formed more readily than a habit which depends
upon visual discrimination. A rough comparison
justifies the statement that it takes from six to
ten times as long for the dancer to learn to choose
the white box as it does to learn to choose the box
on the right. Since this is true, it is exceedingly
important that the possibility of choice by position
or direction of movement be excluded in the case of
tests of brightness discrimination. To indicate
how this was effectively accomplished in the experiments,
the changes in the position of the cardboards made
in the case of a standard set of white-black series
are shown in Table 12. The number of the series,
beginning at the top of the table with the two lettered
preference series, is given in the first column at
the left, the number of the tests at the top of the
table, and the position of the white cardboard, left
or right, is indicated below by the letters l (left)
and r (right).
Copyrights
The Dancing Mouse from Project Gutenberg. Public domain.
