on. So it is with the dreams whose first impulse is some central or
spontaneous excitation. A momentary sight of a face or even the mention
of a name during the preceding day may give the start to dream-activity;
but all subsequent members of the series of images owe their revival to
a tension, so to speak, in the fine threads which bind together, in so
complicated a way, our impressions and ideas.

Among the psychic accompaniments of these central excitations visual
images, as already hinted, fill the most conspicuous place. Even
auditory images, though by no means absent, are much less numerous than
visual. Indeed, when there are the conditions for the former, it
sometimes happens that the auditory effect transforms itself into a
visual effect. An illustration of this occurred in my own experience.
Trying to fall asleep by means of the well-known device of counting, I
suddenly found myself losing my hold on the faint auditory effects, my
imagination transforming them into a visual spectacle, under the form of
a path of light stretching away from me, in which the numbers appeared
under the grotesque form of visible objects, tumbling along in glorious
confusion.

Next to these visual phantasms, certain motor hallucinations seem to be
most prominent in dreams. By a motor hallucination, I mean the illusion
that we are actually moving when there is no peripheral excitation of
the motor organ. Just as the centres concerned in passive sensation are
susceptible of central stimulation, so are the centres concerned in
muscular sensation. A mere impulse in the centres of motor innervation
(if we assume these to be the central seat of the muscular feelings) may
suffice to give rise to a complete representation of a fully executed
movement. And thus in our sleep we seem to walk, ride, float, or fly.

The most common form of motor hallucination is probably the vocal. In
the social encounters which make up so much of our sleep-experience, we
are wont to be very talkative. Now, perhaps, we find ourselves zealously
advocating some cause, now very fierce in denunciation, now very amusing
in witty repartee, and so on. This imagination of ourselves as speaking,
as distinguished from that of hearing others talking, must, it is clear,
involve the excitation of the structures engaged in the production of
the muscular feelings which accompany vocal action, as much as, if not
more than, the auditory centres. And the frequency of this kind