xperiment forces him to make the preliminary
response of attending to the appearance of the door before entering
it. The response of attending to the surface of the door is
substituted for the instinctive response of entering. Otherwise put:
the response of finding the marked door and entering that is
substituted for the response of entering any door at random.

The maze experiment.

An animal is placed in an enclosure from which it can reach food by
following a more or less complicated path. The rat is the favorite
subject for this experiment, but it is a very adaptable type of
experiment and can be tried on any animal. Fishes and even crabs have
mastered simple mazes, and in fact to learn the way to a goal is
probably possible for any species that has any power of learning
whatever. The rat, placed in a maze, explores. He sniffs about, goes
back and forth, enters every passage, and actually covers every square
inch of the maze at least once; and in the course of these
explorations {306} hits upon the food box. Replaced at the starting
point, he proceeds as before, though with more speed and less dallying
in the blind alleys. On successive trials he goes less and less deeply
into a blind alley, till finally he passes the entrance to it without
even turning his head. Thus eliminating the blind alleys one after
another, he comes at length to run by a fixed route from start to
finish.

[Illustration: Fig. 47.--(From Hicks.) Ground plan of a maze used in
experiments on the rat. The central square enclosure is the food box.
The dotted line shows the path taken by a rat on Its fourth trial,
which occupied 4 minutes and 2 seconds.]

At first thought, the elimination of useless moves seems to tell the
whole story of the rat's learning process; but careful study of his
behavior reveals another factor. When the rat approaches a turning
point in the maze, his course bends so as to prepare for the turn; he
does not simply advance to the turning point and then make the turn,
but several steps before he reaches that point are organized or
cooerdinated into a sort of unit.

{307}

[Illustration: Fig. 48.--(From Watson.) Learning curve for the rat
in the maze. This is a composite or average, derived from the
records of four animals. The height of the heavy line above the base
line, for any trial, indicates the number of minutes consumed in
that trial in passing through the maze and reaching the food box.
The