A sensory perception that has the compelling sense of reality of a true perception but that occurs without external stimulation of the relevant sensory organ. Hallucinations should be distinguished from illusions, in which an actual external stimulus is mis-perceived or misinterpreted. The person may or may not have insight into the fact that he or she is having a hallucination.

 Key characteristics of Hallucinations 

  • unwilled – not subject to conscious manipulation
  • has the same qualities as real perception, i.e. vivid, solid
  • perceived as being located in the external world
  • ‘perceptions which arise in the absence of any external stimulus’ (Esquirol, 1833)
  • ‘a false perception which is not in any way a distortion of a real perception but which springs up alongside it’ (Jaspers)



Neurobiology of Hallucinations

Allen P, Laroi F, McGuire PK, et al. The hallucinating brain: a review of structural and functional neuroimaging studies of hallucinations. Neurosci Biobehav Rev. 2008;32:175–91