It is entirely true that subjects under hypnosis frequently recall past forgotten events (or 'repressed' memories in the jargon of psychoanalysis indicating an active role of the individual in forgetting as a defense mechanism).
It is also true that people under hypnosis often 'remember' things quite vividly that never actually happened, but which have great personal significance nonetheless. Psychiatrist William Sargent was one of the first to document the therapeutic benefit of emotionally charged experience, or abreaction, of fantasized life events.
This is one of defining characteristics of deep trance hypnosis in fact, the intensity of fantasies as well as memories, and the inability to distinguish the two. This characteristic of trance is what makes is possible to use hypnotherapy to alter personal history in order to reduce the traumatic effects of past events on an individual's functioning. Not simply a reliving or 'catharsis' of the trauma, but a sometimes a lasting modification of the interpretation of the memory can and does occur in many cases.
This apparent violability and fallibility of human memory is frequently downplayed in discussions of hypnotic recall because of the already difficult time that legitimate victims of abuse have in proving what happened to them. It's not the intention here to make life more difficult for abuse victims, only to point out that hypnosis doesn't neccessarily solve their problem of digging out facts from old memories as neatly as we'd like it to.
The illusion of unusual veracity of hypnotic recall appears to come from at least two main sources:
Recognizing the potential difficulties arising from what some call 'false memory syndrome,' several states in the U.S. now confine legal testimony to that obtained prior to any systematic hypnotic treatment.
In 1985, a committee commissioned by the American Medical Association cautioned against the systematic use of hypnosis for recollection for both its unreliability (the possibility for example of 'confabulation,' the creation of stories out of whole cloth to help fill in missing memories) and its potential to create vivid false memories with an artificially induced sense of certainty.
In addition to the previously provided references for hypermnesia, here are some more specifically devoted to the limitations of hypnotic recall:
No one yet knows exactly how human memory works in all its details, but the view of hypnotic recall as potentially highly fallible is also supported by clinical experience and experimental data.
Milton Erickson called the vivid experiences under hypnosis 'vivification,' and describes how a vivified image is experienced, regardless of whether remembered or constructed:
"... They are subjectively experienced as external events rather than as internal processes, with a consequent endowment of them as reality experiences."
"... They identified it with actual past experiences and thus endowed it with a subjective validity."
"... They 'created a reality' that permitted a responsive functioning in accord with the demands of the experiment."
Are there identified physiological correlates for such vivid recollections or re-creations of past events? One controversial researcher, Michael Persinger, has written hundreds of articles on the subject of neurophysiological correlates of extraordinary experiences of all kinds. He has reportedly reproduced something like ecstatic mystical states with the help of electromagnetic stimulation of the cortical temporal lobes of human subjects, and facilitated vivid imagery akin to UFO abduction experiences. He is not alone in the observation of what is sometimes known as 'clinical mysticism,' which is seen in some forms of temporal lobe epilepsy and in mechanical stimulation of areas of the temporal lobes, but he is somewhat unique in his repeatedly published insistence that all or virtually all unexplained pheonomena and seemingly false memories can be traced to electromagnetic effects on the brain. For an article particularly pertinent to the issue of hypnotic recall, see:
"Six adults, who had recently experienced sudden recall of preschool memories of sex abuse or alien abduction/visitation, were given complete neuropsychological assessments. All experiences "emerged" when hypnosis was utilized within a context of sex abuse or New Age religion and were followed by reduction in anxiety. As a group, these subjects displayed significant (T greater than 70) elevations of childhood imaginings, complex partial epileptic-like signs, and suggestibility. Neuropsychological data indicated right frontotemporal anomalies and reduced access to the right parietal lobe. MMPI profiles were normal. The results support the hypothesis that enhanced imagery due to temporal lobe lability within specific contexts can facilitate the creation of memories; they are strengthened further if there is also reduction in anxiety." (Taken from an on-line abstract).If there is anything to this 'temporal lobe lability' hypothesis, it seems well worthwhile investigating its relationship to hypnotic suggestibility, and the hypothetical 'Fantasy Prone Personality' of Barber and Wilson.
As for recall under hypnosis, the experimental observation seems to be that the subject is uniquely motivated to remember details, but also uniquely capable of making up details and experiencing them as if they were remembered.
In Lynn and Rhue's 1991 Theories of Hypnosis, Robert Nadon et al. discuss a representative example of experiments in eyewitness recall with the aid of hypnosis. Subjects were shown a videotape of a mock armed robbery. They were then asked to recall specific aspects 6 times:
The result was that high hypnotizability subjects (SHSS:C) recalled more cumulative items in hypnosis than they did just before hypnosis. Low hypnotizability subjects did not remember more during hypnosis. This matches our expectation of hypermnesia, that hypnosis facilitates recall for good hypnotic subjects.
Most interestingly, both high and low hypnotizability subjects also made more cumulative errors during hypnosis than just before hypnosis, though the effect was stronger with highly hypnotizable subjects.
One explanation of this kind of result from experiments is that the hypnotic context causes subjects to adopt a looser reporting criterion, and they are motivated to produce more information, containing both correct and incorrect (where there is no clear memory) details. See Klatzky and Erdely, 1985, "The response criterion problem in tests of hypnosis and memory," International Journal of Clinical and Experimental Hypnosis, 33, 246-257 for further discussion of this report criterion issue.
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