A group of highly-suggestible adolescents (n=25) and a group of adolescents with low suggestibility (n=25) followed a hypnotic induction procedure, during which a suggestion of posthypnotic amnesia was given, with the purpose of assessing its influence on autobiographical memory and of investigating if hypnosis-induced amnesia shares the same characteristics as functional amnesia. Statistical analysis confirmed the results of previous studies in the field and, surprisingly, pointed out that even less suggestible participants can be influenced by the suggestion of posthypnotic amnesia. In their case, however, trance levels were more superficial than in the case of highly-suggestible participants.
Keywords: hypnosis, posthypnotic amnesia, autobiographical memory, adolescents
This starting point of this research was Amanda Barnier's study Posthypnotic amnesia for autobiographical episodes: a laboratory model of functional amnesia? (Barnier, 2002) showing that the effect of posthypnotic amnesia suggestion on auto-biographical memory is similar to functional amnesia.
According to DSM-IV, functional amnesia, also known as dissociative autobiographical amnesia, most frequently appears as a memory gap regarding traumatic or highly stressful events:
- in localized amnesia the person cannot remember events taking place during certain well-defined periods of time, generally during the first hours following a traumatic event;
- in selective amnesia the person remembers something, but not all the events occurring during a certain well-defined time period (e.g., a veteran may remember only certain parts of a series of violent fight experiences);
- in generalized amnesia the inability to recall concerns the entire life of the person. People affected by this rare disorder are usually seen in police stations, emergency rooms or in psychiatric facilities.
- continuous amnesia refers to an individual's inability of recalling events subsequent to a certain moment/date.
- systematized amnesia consists of memory loss for a certain category of information such as all the memories related with the individual's family or with a certain person.
Functional amnesia is characterized by:
a) the inability of consciously accessing personal memories (disruption of the explicit memory).
b) the continuing influence of forgotten information on behavior, thought and action (a dissociation between implicit and explicit memory).
c) spontaneous recovery, reflecting altered access, rather than a simple decline of memory over the years caused by normal forgetting (Bryant, 1995; Eich, Macanlay, Loewenstein & Dihle, 1997).
It is labeled functional in order to differentiate it from amnesia associated with medical or organic conditions and to emphasize that, to a certain extent the memory loss serves a psychological goal.
As it is not directed to an objective, forgetfulness appears beyond the individual's control, and it persists even if the person tries to surpass it (Christianson, Nilson, Kopelman et al., 1994; Kihlstrom, Schacter, 1995).
Posthypnotic amnesia is the effect of a suggestion to a hypnotized individual that, after hypnosis, he/she will be unable to remember a certain material until he/she receives a clue to cancel the suggestion. Studies indicate that this induces a deep forgetfulness effect, which has been given various explanations in the literature: strategic, socially motivated response withholding (Coe, 1978; Spanos, 1986), temporary, retrieval-based dissociation between episodic and semantic memory (Kihlstrom, 1985, 1998; Kihlstrom & Barnhardt, 1993), and the output inhibition based on the selective tagging of targeted information as "forbidden" (Huserman, Gruder & Dorest, 1987; Smith, Morton & Oakley, 1998). A series of studies confirmed that posthypnotic amnesia and functional amnesia involve similar memory effects, and that posthypnotic amnesia is the lab model analogous of functional amnesia (Kihlstrom & Schacter, 1995; Barnier & McConkey, 1999; Barnier, 2002). …