Hallucination 

A hallucination is a perception of something that doesn't correspond to external stimuli, and may involve any of the five senses (or any combination of them). It can be the result of a number of causes including drugs, sleep deprivation, psychosis or neurological dysfunction.

Psychiatrists, almost uniformly materialists, believe that hallucinations are caused either by functional defects in the brain or (less often) conflicts within the mind (see defense mechanism[?]).

A rarely expressed but persistent alternate explanation of hallucinations, espoused only by non-materialists, is that "crazy" people can sometimes perceive non-physical phenomena such as angels, visions or the voices of departed spirits or demons.

However one may interpret the causality and reality, i.e. relevance of hallucinations, it seems to be clear that their occurrence strongly correlates with two extremes of sensory activation: either sensory flooding[?] (sensory overload[?]) or sensory deprivation[?]. Both, of course, may be caused by external (as rave party or solitude[?]) or internal factors (as drugs, brain injury[?], illness, or sleep deprivation).

The first usage of the word 'hallucination' in the English language is recorded as by the English physician Sir Thomas Browne in 1642.

Farnsworth, if any one ought to go to a lunatic saying, oh, Patty! oh, Kitty!" "I don't know which I love most, you or Kitty!" and again Farnsworth Patty tried her best to look like a tragedy queen. "But it ISN'T Miss Morton, it's Kitty CLIVE." "Adele said she couldn't remember her last name. But it doesn't Miss Clive,--Kitty Clive,--is--my horse.html">horse!" Patty hesitated a moment, and then gave in, and laughed too. "You must be AWFULLY fond of your horse," she said at last. "I am; Kitty Clive is a wonder, and last summer we rode thousands of And I remember I DID rave about her to Adele. But Adele MUST have not to--" Patty floundered a little, and then concluded her me,--you had no more use for me whatever; because you thought I that you CARE--" "No, I DON'T, Bill! I don't care if you like all the girls in.

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