utton, goes out and starts to eat,
requiring but a second or two for the whole complex reaction. Perhaps
15 or 20 trials have been required to reach this stage of prompt,
unerring response. The course of improvement is rather irregular, with
ups and downs, but with no sudden shift from the varied reaction of
the first trial to the fixed reaction of the last. The learning
process has been gradual.

This is the typical instance of learning by "trial and error", which
can be defined as varied reaction with gradual elimination of the
unsuccessful responses and fixation of the successful one. It is also
a case of the substitute response. At first, the cat responds to the
situation by reaching or pushing straight towards the food, but it
learns to substitute for this most instinctive response the less
direct response of going to another part of the cage and turning a
button.

The cat in this experiment is evidently trying to get out of the cage
and reach the food. The situation of being confined in a cage while
hungry arouses an impulse or tendency to get out; but this tendency,
unable at once to reach its goal, is dammed up, and remains as an
inner directive force, facilitating reactions that are in the line of
escape and inhibiting other reactions. When the successful response is
hit upon, and the door opened, the dammed-up energy is discharged into
this response; and, by repetition, {310} the successful response
becomes closely attached to the escape-tendency, so as to occur
promptly whenever the tendency is aroused.

There is no evidence that the cat reasons his way out of the cage. His
behavior is impulsive, not deliberative. There is not even any
evidence that the cat clearly observes how he gets out. If he made a
clean-cut observation of the manner of escape, his time for escaping
should thereupon take a sudden drop, instead of falling off gradually
and irregularly from trial to trial, as it does fall off. Trial and
error learning is learning by doing, and not by reasoning or
observing. The cat learns to get out by getting out, not by seeing how
to get out.

Summary of Animal Learning

Let us take account of stock at this point, before passing to human
learning, and attempt to generalize what we have observed in animals
of the process of learning.

(1) _Elimination_ of a response, which means _detachment_ of a
response from the stimulus that originally aroused it, occurs in three
main cases:

(a) Elimina