Amnesia (basically selective forgetting in this case) sometimes occurs pontaneously in hypnosis, and sometimes happens as the result of a direct or indirect suggestion to forget something. The amnesia effect may last a variable time, possibly months or longer, depending on the psychological ignificance of the amnesia and the forgotten material and on the intensity of ttempts to recall and availability of recall cues in the environment.
A posthypnotic suggestion in general is a response to hypnotic suggestion that xtends beyond the boundary of the actual trance period. Posthypnotic uggestions are often performed without any knowledge that they were previously suggested (thus the neccessary link to hypnotic amnesia of this phenomena). The individual responding to a posthypnotic suggestion and with amnesia for the source of the suggestion will generally incorporate the esponse into their ongoing activities without disruption, in a similar manner o rituallized actions that we pay little attention to such as brushing our teeth n the morning or making the right sequence of turns in our well established oute to work each morning. If the response involves some bizarre action, the ndividual will either be confused or typically will come up with a creative ationalization for the behavior. Very rarely will there be any awareness of the ction resulting from a previous suggestion.
t is the contention of many experts in hypnotic work that individuals can and do resist posthypnotic suggestions that they do not wish to perform, except hat implicit trust of the hypnotist may promote a behavior out of the ordinary. This is sometimes (especially per Orne) considered more a factor of i -J A
addition to the Hilgard article in Vol. 16 of Annual Reviews (1965), cited above:
• W. Wells, 1940, "The extent and duration of post-hypnotic amnesia," Journal of Psychology, 9:137-151.
• Edwards, 1963, "Duration of post-hypnotic effect," British Journal of Psychiatry, 109: 259-266.
• Dixon, 1981, "Preconscious Processing" (book)
Various studies have also been done to try to determine what kinds of psychological pressure will cause hypnotic amnesia to be breached, and under what conditions.
Schuyler & Coe, "A physiological investigation of volitional and nonvolitional experience during posthypnotic amnesia," Journal of Personality & Social Psychology, 40(6):1160-9, 1981 Jun was a good xample.
Highly responsive hypnotic subjects, who were classified as having control over remembering (voluntaries) or not having control over remembering (involuntaries) during posthypnotic amnesia, were compared with each other on four physiological measures (heart rate, electrodermal response, espiration rate, muscle tension) during posthypnotic recall. Two contextual onditions were employed: One was meant to create pressure to breach posthypnotic amnesia (lie detector instructions); the other, a relax condition, erved as a control. The recall data confirmed earlier findings of Howard and Coe and showed that voluntary subjects under the lie detector condition ecalled more than the other three samples that did not differ from each other. However, using another measure of voluntariness showed that both voluntary nd involuntary subjects breached under lie detector conditions. Electrodermal response supported the subjects' reports of control in this case. Physiological measures were otherwise insignificant. The results are discussed as they relate to (a) studies attempting to breach posthypnotic amnesia, (b) the voluntary/involuntary classification of subjects, and (c) heories of hypnosis.
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