Hypnagogic
imagery occurs during the nodding off stage, and can
vary considerably, from startling warnings and vivid
precognition, to static scenes. Sometimes voices are
heard, even entire conversations. In sleep research
generally, the hypnagogic state is perhaps underestimated.
Researchers tend to accept that it represents the first
stage of sleep, but are more interested in other sleep
phenomena. This underpins the point that, as far as
knowledge about sleep and dreams is concerned, we are
merely scratching the surface. Within the realm of hypnagogic
imagery lies a mysterious world that, if better understood,
can offer considerable rewards.
Hypnagogic images, according to some, are the result
of the visual system "attempting to make sense" of the
visual input still available to the eyes when the mind
is drifting toward sleep. Even in very low ambient light
levels, light penetrates the eyelids, making the patterns
of blood flow through them visible. This is the basis
for an "interpretation" by the visual system. The visual
system may attempt to "force" the input to correspond
to, say, a geometrical pattern, or the semblance of
some object. Dream images or memory images may intrude
into such images.
Precognitive visions seen during hypnagogic imagery
are said to be particularly reliable and rarely need
interpreting because, usually, they closely resemble
future events fairly accurately.
