Carl%20Sagan%20-%20The%20Demon%20Haunted%20World

Hallucinations
outside, however, images of the objects in the room behind
him can be seen reflected dimly in the window glass. For a
time he may see either the garden (if he gazes into the
distance) or the reflection of the room's interior (if he focuses
on the glass a few inches from his face). Night falls, but the
fire still burns brightly in the fireplace and illuminates the
room. The watcher now sees in the glass a vivid reflection of
the interior of the room behind him, which appears to be
outside the window. This illusion becomes dimmer as the fire
dies down, and, finally, when it is dark both outside and
within, nothing more is seen. If the fire flares up from time to
time, the visions in the glass reappear.
In an analogous way, hallucinatory experiences such as those
of normal dreams occur when the 'daylight' (sensory input) is
reduced while the 'interior illumination' (general level of brain
arousal) remains 'bright', and images originating within the
'rooms' of our brains may be perceived (hallucinated) as though
they came from outside the 'windows' of our senses.
Another analogy might be that dreams, like the stars, are
shining all the time. Though the stars are not often seen by day,
since the sun shines too brightly, if, during the day, there is an
eclipse of the sun, or if a viewer chooses to be watchful awhile
after sunset or awhile before sunrise, or if he is awakened from
time to time on a clear night to look at the sky, then the stars,
like dreams, though often forgotten, may always be seen.
A more brain-related concept is that of a continuous
information-processing activity (a kind of 'preconscious
stream') that is influenced continually by both conscious and
unconscious forces and that constitutes the potential supply
of dream content. The dream is an experience during which,
for a few minutes, the individual has some awareness of the
stream of data being processed. Hallucinations in the waking
state also would involve the same phenomenon, produced by
a somewhat different set of psychological or physiological
circumstances . . .
It appears that all human behaviour and experience (normal
as well as abnormal) is well attended by illusory and hallucinatory
phenomena. While the relationship of these phenomena to
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