e me, I observe that his eyes are brown in response to a
visual stimulus; but I later recall this fact in response simply to
the name "John", or in response to the question as to what is the
color of John's eyes. I see what a square is by seeing squares and
handling them, and later I get this idea simply in response to the
word "square" in conversation or reading.

Memory Images

Now, can _sensations_ be recalled, can they be aroused except by their
natural sensory stimuli? Can you recall the color blue, or the sound
of a bugle, or the odor of camphor, or the feel of a lump of ice held
in the hand? Almost every one will reply "Yes" to some at least of
these questions. One may have a vivid picture of a scene before the
"mind's eye", and another a realistic sound in the "mind's ear", and
they may report that the recalled experience seems essentially the
same as the original sensation. Therefore, sensory reactions are no
exception to the rule of recall by a substitute stimulus.

A sensation or complex of sensations recalled by a substitute stimulus
is called a "mental image" or a "memory image".

Individuals seem to differ in the vividness or realism of their memory
images--the likeness of the image to an actual sensation--more than in
any other respect. Galton, in taking a sort of census of mental
imagery, asked many persons to call up the appearance of their
breakfast table as they had sat down to it that morning, and to
observe how lifelike the image was, how complete, how adequate in
respect to color, how steady and lasting, and to compare {369} the
image in these respects with the sensory experience aroused by the
actual presence of the scene. Some individuals reported that the image
was "in all respects the same as an original sensation", while others
denied that they got anything at all in the way of recalled sensation,
though they could perfectly well recall definite facts that they had
observed regarding the breakfast table. The majority of people gave
testimony intermediate between these extremes.

Individuals differ so much in this respect that they scarcely credit
each other's testimony. Some who had practically zero imagery held
that the "picture before the mind's eye" spoken of by the poets was a
myth or mere figure of speech; while those who were accustomed to
vivid images could not understand what the others could possibly mean
by "remembering facts about the breakfast table without having any
image