DEFINITION

• 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.