While I believe there may be some anatomical evidence for some of this,
the reports of hallucinators are not reliable. They may be simply
mistaken about the nature of the experiences they are having.
Some philosophers would argue that it is impossible for someone to be
mistaken about the nature of his perceptions, but I disagree. If a
hallucinator thinks he is seeing a purer red than he has ever seen before,
it could be that in some sense the red is actually the same as what he
has always seen, but that part of his mind which judges purity is not
working properly. Similarly, if he thinks he is seeing a mandala of
infinite fractal complexity, and is simultaneously perceiving every
minute detail far beyond the resolution he is normally capable of,
again I would suggest that he may be simply misjudging how much detail
he is actually perceiving.
The same thing happens when the hallucinator hits upon a thought which
strikes him as incredibly meaningful and insightful. Often, in the
aftermath, he realizes that the idea was actually rather prosaic.
What all these cases have in common is that the part of the mind which
evaluates the nature of the perception seems to be affected, so that the
perception is judged as being more "special" than it actually is.
This is not to argue that all hallucinatory reports are mistaken, simply
that we cannot take them at face value given that the brain is not working
normally.
Hal