A hallucination is a **** in the absence of external stimulus that has qualities of real pe****tion. Hallucinations are vivid, substantial, and are seen to be located in external objective space. They are distinguishable from these related phenomena: dreaming, which does not involve wakefulness; illusion, which involves distorted or misinterpreted real pe****tion; imagery, which does not mimic real pe****tion and is under voluntary control; and pseudohallucination, which does not mimic real pe****tion, but is not under voluntary control. Hallucinations also differ from "delusional pe****tions", in which a correctly sensed and interpreted stimulus (i.e., a real pe****tion) is given some additional (and typically absurd) significance.