Traci Speed, M.D., Ph.D., Thomas Sedlak, M.D., Ph.D.


  • An hallucination is a perception without a stimulus.
    • With true hallucinations, the individual is convinced of the reality of the experience.
  • A true hallucination must be differentiated from:
    • Illusion - a misinterpretation of a stimulus (e.g., a crack on the floor is misperceived as a snake)
    • Pseudohallucination - occurs in inner subjective space (e.g., heard in one’s thoughts, not perceived as auditory, does not come through the ears)
    • Vivid imagery – increased imagination or mental images
  • Hallucinations can occur in any of the five senses (auditory, visual, olfactory, gustatory, and/or tactile).
    • Auditory hallucinations are the most common.
  • Hallucinations are not pathognomic for any specific psychiatric illness, including schizophrenia[1].
  • Hypnagogic and hypnopompic hallucinations can occur in healthy people when falling asleep and awakening, respectively.

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Last updated: September 3, 2017