Experimental Studies

Right from the beginning of the modern era, a great deal of research effort has been devoted to claims that hypnotic suggestions enable individuals to transcend their normal voluntary capacities—to be stronger, see better, learn faster, and remember more. However, research has largely failed to find evidence that hypnosis can enhance human performance. Many early studies, which seemed to yield positive results for hypnosis, possessed serious methodological flaws, such as the failure to collect adequate baseline information. In general, it appears that hypnotic suggestions for increased muscular strength, endurance, sensory acuity, or learning do not exceed what can be accomplished by motivated subjects outside hypnosis.

A special case of performance enhancement has to do with hypnotic suggestions for improvements in memory—what is known as hypnotic hypermnesia. Hypermnesia suggestions are sometimes used in forensic situations, with forgetful witnesses and victims, or in therapeutic situations to help patients remember traumatic personal experiences. Although field studies have sometimes claimed that hypnosis can powerfully enhance memory, these anecdotal reports have not been duplicated under laboratory conditions.

A 1994 report by the Committee on Techniques for the Enhancement of Human Performance, a unit of the U.S. National Research Council, concluded that gains in recall produced by hypnotic suggestion were rarely dramatic and were matched by gains observed even when subjects are not hypnotized (in fact, there is some evidence that hypnotic suggestion can interfere with normal hypermnesic processes). To make things worse, any increases obtained in valid recollection are met or exceeded by increases in false recollec tions. Moreover, hypnotized subjects (especially those who are highly hypnotizable) may be vulnerable to distortions in memory produced by leading questions and other subtle and suggestive influences.

Similar conclusions apply to hypnotic age regression, in which subjects receive suggestions that they are returning to a previous period in their lives (this is also a technique used clinically to foster the retrieval of forgotten memories of child abuse). Although age-regressed subjects may experience themselves as children, and may behave in a childlike manner, there is no evidence that they actually undergo either abolition of characteristically adult modes of mental functioning or reinstatement of childlike modes of mental functioning. Nor do age-regressed subjects experience the revivification of forgotten memories of childhood.

One phenomenon that has received a great deal of attention is hypnotic analgesia—in large part because of the obvious clinical uses to which it can be put. A comparative study of experimental pain found that among hypnotizable subjects, hypnotic analgesia was superior to morphine, diazepam, aspirin, acupuncture, and biofeedback. Hypnotic analgesia relieves both sensory pain and suffering. It is not mediated by relaxation, and the fact that it is not reversed by narcotic antagonists would seem to rule out a role for endogenous opiates. There is a placebo component to all active analgesic agents, and hypnosis is no exception; however, hypnotizable subjects receive benefits from hypnotic suggestion that outweigh what they or their insusceptible counterparts achieve from plausible placebos.

Psychological explanations of hypnotic analgesia come in two primary forms. On the one hand, it is argued that hypnotized subjects use such techniques as self-distraction, stress-inoculation, cognitive reinterpretation, and tension management. While there is no doubt that cognitive strategies can reduce pain, their success, unlike the success of hypnotic suggestions, is not correlated with hypnotizability and thus is unlikely to be responsible for the effects observed in hypnotizable subjects. Rather, hypnotic analgesia seems to be associated with a division of consciousness which prevents the perception of pain from being represented in conscious awareness, without altering the physiological effects of the pain stimulus.

A great deal of research has also been devoted to the posthypnotic amnesia frequently displayed by hypno-tizable subjects. This form of forgetting does not occur

Hypnosis and the Psychological Unconscious spontaneously and may be reversed by administration of a prearranged signal without the reinduction of hypnosis, so it does not represent a form of state-dependent learning. However, the reversibility of amnesia does indicate that its mechanisms may be located at the retrieval stage of memory processing, rather than at the encoding or storage stages. Posthypnotic amnesia does not prevent words studied during hypnosis from being used as free associates or category instances, indicating that posthypnotic amnesia is a disruption of episodic, but not semantic, memory. Moreover, the production of studied items as instances and associates is actually facilitated, resulting in priming effects. Similarly, post-hypnotic amnesia does not affect retroactive inhibition or savings in relearning. Skills acquired during hypnosis are preserved afterward, even though the subject cannot remember the acquisition trials. This assortment of findings indicates that although post-hypnotic amnesia disrupts explicit expressions of episodic memory (such as recall), it spares implicit expressions.

Other phenomena of hypnosis can also be understood in terms of the explicit - implicit distinction. For example, hypnotizable subjects given suggestions for deafness deny hearing anything; yet they show speech dysfluencies under conditions of delayed auditory feedback. And when given suggestions for blindness, they deny seeing anything, yet show priming effects from stimuli presented in their visual fields. With the analogy between explicit and implicit memory, we may say that hypnotic suggestions for blindness, deafness, and the like impair explicit perception while sparing implicit perception.


Hypnosis has been used in clinics for both medical and psychotherapeutic purposes. By far the most successful and best documented of these has been hypnotic analgesia for the relief of pain. Clinical studies indicate that hypnosis can effectively relieve pain in patients suffering pain from burns, cancer and leukemia (e.g., bone marrow aspirations), childbirth, and dental procedures. In such circumstances, as many as one half of an unselected patient population can obtain significant, if not total, pain relief from hypnosis. Hypnosis may be especially useful in cases of chronic pain, where chemical analgesics such as morphine pose risks of tolerance and addiction. Hypnosis has also been used, somewhat heroically perhaps, as the sole analgesic agent in abdominal, breast, cardiac, and genitourinary surgery, and in orthopedic situations, although it seems unlikely that more than about 10% of patients can tolerate major medical procedures with hypnosis alone.

Hypnotic suggestion can have psychosomatic effects, a matter that should be of some interest to psy-chophysiologists and psychoneuroimmunologists. For example, several well controlled laboratory and clinical studies have shown that hypnotic suggestion can affect allergic responses, asthma, and the remission of warts. A famous case study convincingly documented the positive effects of hypnotic suggestion on an intractable case of congenital ichthyosiform erythro-derma, a particularly aggressive skin disorder. Such successes have led some practitioners to offer hypnosis in the treatment of cancer. While there is some evidence that hypnosis can have effects on immunologi-cal processes, more research in this area is needed, and hypnosis should never be substituted for conventional medical treatments in such cases.

Hypnosis has also been used in psychotherapy, whether psychodynamic or cognitive - behavioral in orientation. In the former case, hypnosis is used to promote relaxation, enhance imagery, and generally loosen the flow of free associations (some psycho-dynamic theorists consider hypnosis to be a form of adaptive regression or regression in the service of the ego). However, there is little evidence from controlled outcome studies that hypnoanalysis or hypnotherapy are more effective than nonhypnotic forms of the same treatment. By contrast, a 1995 meta-analysis by Kirsch and colleagues showed a significant advantage when hypnosis is used adjunctively in cognitive - behavioral therapy for a number of problems. In an era of managed mental health care, it will be increasingly incumbent on practitioners who use hypnosis to document, quantitatively, the clinical benefits of doing so. [See Behavior Therapy; Cognitive Therapy; Psychoanalysis.]

Hypnosis is sometimes used therapeutically to recover forgotten incidents, as for example in cases of child sexual abuse. Although the literature contains a number of dramatic reports of the successful use of this technique, most of these reports are anecdotal and fail to obtain independent corroboration of the

Hypnosis and the Psychological Unconscious memories that emerge. Given what we know about the unreliability of hypnotic hypermnesia, and the risk of increased responsiveness to leading questions and other sources of bias and distortion, such clinical practices are not recommended. Similar considerations obtain in forensic situations. In fact, many legal jurisdictions severely limit the introduction of memories recovered through hypnosis out of a concern that such evidence might be tainted. The Federal Bureau of Investigation has published a set of guidelines for those who wish to use hypnosis forensically, and similar precautions should be used in the clinic. [See Child Sexual Abuse.]

Returning to strictly therapeutic situations, an important but unresolved issue is the role played by individual differences in the clinical effectiveness of hypnosis. As in the laboratory, so in the clinic: a genuine effect of hypnosis should be correlated with hypno-tizability. It is possible that many clinical benefits of hypnosis are mediated by placebo-like motivational and expectational processes—that is, with the "ceremony" surrounding hypnosis, rather than with hypnosis per se. An analogy is to hypnotic analgesia, which appears to have a placebo component available to insusceptible and hypnotizable individuals alike, and a dissociative component available only to those who are highly hypnotizable. Unfortunately, clinical practitioners are often reluctant to assess hypnotiza-bility in their patients and clients out of a concern that low scores might reduce motivation for treatment. This danger is probably exaggerated. On the contrary, assessment of hypnotizability by clinicians contemplating the therapeutic use of hypnosis would seem to be no different, in principle, than an assessment of allergic responses before prescribing an antibiotic. In both cases, the legitimate goal is to determine what treatment is appropriate for what patient.

It should be noted that clinicians sometimes use hypnosis in nonhypnotic ways—practices which tend to support the hypothesis that whatever effects they achieve through hypnosis are related to its placebo component. There is nothing particularly hypnotic, for example, about having a patient in a smoking-cessation treatment rehearse therapeutic injunctions not to smoke and other coping strategies while hypnotized. It is likely that more successful use of hypnosis as an adjunct to the cognitive - behavioral treatment of smoking, excessive weight, and similar habit disorders would be to use hypnotic suggestions to con trol the patient's awareness of cravings for nicotine, sweets, and the like. Given the ability of hypnotic suggestions to control conscious perception and memory, such strategies might well have therapeutic advantage—but only, of course, for those patients who are hypnotizable enough to respond positively to such suggestions.

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