hypnotically induced hallucination

   Also referred to as hypnotic hallucination and induced hallucination. The first two terms refer to the notion of hypnosis, which is in turn indebted to the Greek noun hupnos (sleep). The term hypnotically induced hallucination is used to denote a vivid hallucination that can be evoked in another person through suggestion. The phenomenon has been described since the era of mesmerism. It is often experienced in the visual modality, but it can manifest itself in any of the sensory modalities, as well as in various sensory modalities simultaneously. In the latter case, it is referred to as a " compound hallucination. When it replaces the entire sensory input pic-ture,itisknown as a "panoramic or "scenic hallucination. These elaborate types of hallucinations are also referred to as lucid dreams. As noted by the French scientists Charles Féré (1852-1907) and Alfred Binet (1857-1911), hypnotically induced hallucinations occurring in the visual modality tend to be experienced under the same phenomenological conditions as ordinary sense perceptions. Binet found, for example, that a screen placed before the eyes of an individual with hypnotically induced visual hallucinations may entail the cessation of that hallucination, as would have been the case with an actual object disappearing behind the screen, while in other cases the hallucinations are projected upon the screen. Binet also noted that in some individuals with a unilateral "colour vision deficiency it is impossible to suggest a coloured hallucination to the colour-blind eye, whereas in others this suggestion proves successful. In conformity with the findings of the Scottish physicist David Brewster (1781-1868), Binet also noted that hypnotically induced visual hallucinations can be doubled by exerting mechanical pressure on the eye with the aid of a prism. Using a spy glass can yield a magnification of these hallucinations or obstruct the percipient's view, whereas mirrors tend to reflect them in accordance with the laws of physics. Experimental research carried out by the American psychologist Cheves West Perky (1874-1940) with the aid of projected images would seem to corroborate these findings. When it was suggested to hypnotized individuals that they might hallucinate a certain shape, they were barely influenced by the presence or absence of a projected image of that particular shape. As the Australian psychologists Richard A. Bryant and David Mallard maintain, "Participants who had the projection absent and then present reported comparable reality and vividness ratings when the projection was absent and present. These findings indicate that elevated hypnotiz-ability and hypnosis are associated with attributions of external reality to suggested experiences." This phenomenon is known as the "Perky effect.

   References

   Binet, A. (1884). Visual hallucinations in hypnotism. Mind, 9, 413-415.

   Brady, J.P., Levitt, E.E. (1966). Hypnotically induced visual hallucinations. Psychosomatic Medicine, 28, 351-163.

   Bryant, R.A., Mallard, D. (2003). Seeing is believing: The reality of hypnotic hallucinations. Consciousness and Cognition, 12, 219-230.

   Perky, C.W. (1910). An experimental study of imagination. American Journal of Psychology, 21, 422-452.