images or of ideas of your past.
Images Vary as to Type.—We do not all remember what we call the same fact
in like images or ideas. When you remembered that Columbus discovered
America in 1492, some of you had an image of Columbus the mariner standing
on the deck of his ship, as the old picture shows him; and accompanying this
image was an idea of "long agoness." Others, in recalling the same fact, had an
image of the coast on which he landed, and perchance felt the rocking of the boat
and heard it scraping on the sand as it neared the shore. And still others saw on
the printed page the words stating that Columbus discovered America in 1492.
And so in an infinite variety of images or ideas we may remember what we call
the same fact, though of course the fact is not really the same fact to any two of
us, nor to any one of us when it comes to us on different occasions in different
images.
Other Memory Material.—But sensory images are not the only material with
which memory has to deal. We may also recall the bare fact that it rained a week
ago today without having images of the rain. We may recall that Columbus
discovered America in 1492 without visual or other images of the event. As a
matter of fact we do constantly recall many facts of abstract nature, such as
mathematical or scientific formulæ with no imagery other than that of the words
or symbols, if indeed these be present. Memory may therefore use as its stuff not
only images, but also a wide range of facts, ideas and meanings of all sorts.
4. LAWS UNDERLYING MEMORY
The development of a good memory depends in no small degree on the closeness
with which we follow certain well-demonstrated laws.
The Law of Association.—The law of association, as we have already seen, is
fundamental. Upon it the whole structure of memory depends. Stating this law in
neural terms we may say: Brain areas which are active together at the same time
tend to establish associative paths, so that when one of them is again active the
other is also brought into activity. Expressing the same truth in mental terms: If
two facts or experiences occur together in consciousness, and one of them is
later recalled, it tends to cause the other to appear also.
The Law of Repetition.—The law of repetition is but a restatement of the law
of habit, and may be formulated as follows: The more frequently a certain
cortical activity occurs, the more easily is its repetition brought about. Stating