When you think of hypnosis, you may envision people completely under the power of a hypnotist, who is ordering them to dance like a chicken or perhaps “regress” to early childhood and talk in childlike voices. Many common beliefs about hypnosis are false. Hypnosis refers to a social interaction in which one person (the hypnotist) makes suggestions that lead to a change in another person’s (the subject’s) subjective experience of the world (Kirsch et al., 2011). The essence of hypnosis is in leading people to expect that certain things will happen to them that are outside their conscious will (Wegner, 2002).

To induce hypnosis, a hypnotist may ask the person to be hypnotized to sit quietly and focus on some item, such as a spot on the wall (or a swinging pocket watch), and then make suggestions to the person about what effects hypnosis will have (e.g., “your eyelids are slowly closing” or “your arms are getting heavy”). Even without hypnosis, some suggested behaviors might commonly happen just because a person is concentrating on them—just thinking about their eyelids slowly closing, for instance, may make many people shut their eyes briefly or at least blink. In hypnosis, however, suggestions may be made—and followed by people in a susceptible state of mind—for very unusual behavior that most people would not normally do, such as flapping their arms and making loud clucking sounds.

Not everyone is equally hypnotizable. Susceptibility varies greatly. Some highly suggestible people are very easily hypnotized, most people are only moderately influenced, and some people are entirely unaffected by attempts at hypnosis. One of the best indicators of a person’s susceptibility is the person’s own judgment. So, if you think you might be hypnotizable, you may well be (Hilgard, 1965). People with active, vivid imaginations or people who are easily absorbed in activities such as watching a movie are also somewhat more prone to be good candidates for hypnosis (Sheehan, 1979; Tellegen & Atkinson, 1974).

From watching stage hypnotism, you might think that the major effect of hypnosis is making people do peculiar things. So what do we actually know to be true about hypnosis? There are some impressive demonstrations that suggest real changes occur in those under hypnosis. At the 1849 festivities for Prince Albert of England’s birthday, for example, a hypnotized guest was asked to ignore any loud noises and then didn’t even flinch when a pistol was fired near his face. Other stage hypnotists claim that their volunteers can perform feats of superhuman strength under hypnosis, such as becoming “stiff as a board” and lying unsupported with shoulders on one chair and feet on another while the hypnotist stands on the hypnotized person’s body.

Studies have demonstrated that hypnosis can undermine memory, but with important limitations. People susceptible to hypnosis can be led to experience posthypnotic amnesia, the failure to retrieve memories following hypnotic suggestions to forget. Ernest Hilgard (1986) taught a hypnotized person the populations of some remote cities, for example, and then suggested that the participant forget the study session; the person was quite surprised after the session at being able to give the census figures correctly. Asked how he knew the answers, the individual decided he might have learned them from a TV program. Such amnesia can then be reversed in subsequent hypnosis.

Importantly, research has found that only memories that were lost under hypnosis can be retrieved through hypnosis. The false claim that hypnosis helps people to unearth memories that they are not able to retrieve in normal consciousness seems to have surfaced because hypnotized people often make up memories to satisfy the hypnotist’s suggestions. For example, Paul Ingram, a sheriff ’s deputy accused of sexual abuse by his daughters in the 1980s, was asked by interrogators in session after session to relax and imagine having committed the crimes. He emerged from these sessions having confessed to dozens of horrendous acts of “satanic ritual abuse.” These confessions were called into question, however, when independent investigator Richard Ofshe used the same technique to ask Ingram about a crime that Ofshe had simply made up out of thin air, something of which Ingram had never been accused. Ingram produced a three-page handwritten confession, complete with dialogue (Ofshe, 1992). Still, prosecutors in the case accepted Ingram’s guilty plea, and he was only released in 2003 after a public outcry and years of work on his defense. After a person claims to remember something, even under hypnosis, it is difficult to convince others that the memory was false (Loftus & Ketchum, 1994).

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Hypnosis can lead to measurable physical and behavioral changes in the body. One well-established effect is hypnotic analgesia, the reduction of pain through hypnosis in people who are susceptible to hypnosis. For example, one study (see FIGURE 5.11) found that for pain induced in volunteers in the laboratory, hypnosis was more effective than morphine, diazepam (Valium), aspirin, acupuncture, or placebos (Stern et al., 1977). For people who are hypnotically susceptible, hypnosis can be used to control pain in surgeries and dental procedures, in some cases more effectively than any form of anesthesia (Druckman & Bjork, 1994; Kihlstrom, 1985).

Hypnosis also has been shown to enable people to control mental processes previously believed to be beyond conscious control. For instance, the Stroop task (Stroop, 1935) is a classic psychological test in which a person is asked to name the color of words on a page (appearing in ink that is red, blue, green, etc.). This is a simple task. However, sometimes the words themselves are the names of colors, but they are printed in a different color of the ink. It turns out that people are significantly slower and make more errors, when naming ink colors that don’t match the content of the word (e.g., when the word “green” is written in red ink) than if the content is neutral or congruent (e.g., if the word “desk” or “red” is written in red ink). This effect is present no matter how hard we try. Amazingly, the effect is completely eliminated when highly suggestible people are hypnotized and told to respond to all words the same way (Raz et al., 2002). Importantly, though, follow-up studies have revealed that hypnotic induction is not required to eliminate the Stroop effect. It turns out that simply suggesting to highly suggestible people that they should respond to all words the same has the same effect as hypnosis (Lifshitz et al., 2013). This suggests that hypnotic effects may be the result of highly suggestible people complying with the suggestions of others.

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Nevertheless, people under hypnotic suggestion are not merely telling the hypnotist what the hypnotist wants to hear. Instead, they seem to be experiencing what they have been asked to experience. Under hypnotic suggestion, for example, regions of the brain responsible for color vision are activated in highly hypnotizable people when they are asked to perceive color, even when they are really shown gray stimuli (Kosslyn et al., 2000). While engaged in the Stroop task, people who can eliminate the Stroop effect under suggestion show decreased activity in the anterior cingulate cortex (ACC), the part of the brain involved in conflict monitoring (FIGURE 5.12; Raz, Fan, & Posner, 2005), consistent with the lack of conflict perceived between the color name and ink. Overall, hypnotic suggestion appears to change the subjective perception of those experiencing it, as reflected by changes in their self-report, behavior, and brain activity.

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