be chosen alternately on the right and on the left.
In order that the entire series of ten tests, and
sometimes two such series given on consecutive days,
might be available as indications of the duration
of a habit, the mouse was permitted to enter and pass
through either of the electric-boxes without receiving
a shock. Had the shock been given as punishment
for a wrong choice, it is obvious that only the first
test of the memory series would be of value as an
indication of the existence of a previously acquired
habit. Even under the conditions of no shock
and no stop or hindrance the first test of each memory
series is of preeminent importance, for the mouse tends
to persist in choosing either the side or the visual
condition (sometimes one, sometimes the other) which
it chooses in the first test. If the wrong box
is chosen to begin with, mistakes are likely to continue
because of the lack of punishment; in this case the
animal discriminates, but there is no evidence that
it remembers the right box. Likewise, if the right
electric-box is chosen in the first test, correct
choices may continue simply because the animal has
discovered that it can safely enter that particular
box; again, the animal discriminates without depending
necessarily upon its earlier experience. I have
occasionally observed a series of ten correct choices,
made on the basis of an accidental right start, followed
by another series in which almost every choice was
wrong, because the animal happened to start wrong.
As the results of my tests of memory are of such a
nature that they cannot advantageously be averaged,
I have arranged in Table 48 a number of typical measurements
of the duration of visual discrimination habits.
In this table I have indicated the number and age
of the individual tested, the habit of discrimination
which had been acquired, the length of the rest interval,
the result of the first test (right or wrong), and
the number of errors made in each series of ten memory
tests.
MEASUREMENTS OF THE DURATION OF A HABIT
Memory
ERRORS
NO. AGE NAME OF TEST REST FIRST FIRST SECOND
INTERVAL CHOICE SERIES SERIES
1000 25 weeks White-black 4 weeks Right
0
5 27 White-black
4 Right 5 7 210 15 White-black
8 Right 5 220 15 White-black
8 Right 4 230 15 White-black
8 Wrong 5 215 15 White-black
8 Right 5 225 15 White-black
8 Right 2 235 15 White-black
8 Right 7 410 15 White-black
8 Wrong 4 415 15 White-black
8 Wrong 6 420 15 White-black
8 Wrong 3 425 15 White-black
8 Right 3
