the scenes being shifted in the middle of a
{500} speech, and a character who starts in as one person merging
presently into somebody else. Dreams follow the definition of
imagination or invention, in that materials recalled from different
contexts are put together into combinations and rearrangements never
before experienced. The combinations are often bizarre and
incongruous.

Perhaps the most striking characteristic of dreams is their seeming
reality while they last. They seem real in spite of their incongruity,
because of the absence of critical ability during sleep. In waking
life, when the sight of one object reminds me of another and calls up
an image of that other, I know that the image is an image, and I know
I have thought of two different things. In sleep the same recall by
association occurs, but the image is forthwith accepted as real; and
thus things from different sources get together in the same dream
scene, and a character who reminds us of another person forthwith
becomes that other person. We are not mentally active enough in sleep
to hold our images apart. Associative recall, with blending of the
recalled material, and with entire absence of criticism, describes the
process of dreaming.

What is the _stimulus_, to which the dream responds? Sometimes there
is an actual sensory stimulus, like the alarm clock or a stomach ache;
and in this case the dream comes under the definition of an illusion;
it is a false perception, more grotesquely false than most illusions
of the day. A boy wakes up one June morning from a dream of the Day of
Judgement, with the last trump pealing forth and blinding radiance all
about--only to find, when fully awake, that the sun is shining in his
face and the brickyard whistle blowing the hour of four-thirty a.m.
This was a false perception. More often, a dream resembles a daydream
in being a _train of thoughts and images_ without much relation to
present sensory stimuli; and then the dream {501} would come under the
definition of hallucination instead of illusion.

Sometimes a sensory stimulus breaks in upon a dream that is in
progress, and is interpreted in the light of this dream. In one
experiment, the dreamer, who was an authoress, was in the midst of a
dream in which she was discussing vacation plans with a party of
friends, when the experimenter disturbed her by declaiming a poem; in
her dream this took the form of a messenger from her publisher,
reciting something a