Hypnosis and Eyewitness Memory

The use of hypnosis to enhance the memory of a witness to a crime often results not only in some additional accurate recall of information about the event but also in the incorporation of additional misinformation into the witness’s memory of the event and a general increase in his or her confidence in the veracity of recall. Research has shown that hypnosis increases the amount of information that is recalled about an event. This effect often occurs with other techniques also, such as the cognitive interview. When techniques such as hypnosis and the cognitive interview are used to enhance a witness’s memory, the amount of new information recalled turns out to be a mixture of accurate and inaccurate information. Furthermore, once accurate and inaccurate information get mixed into a coherent narrative, the witness is typically not very good at distinguishing those aspects of the story that are true from those that are false. The additional information will make the narrative the witness is trying to construct more coherent, and his or her confidence in it will increase. The witness’s memory has not been refreshed. A more coherent narrative has been constructed that the witness feels is a more accurate representation of the event he or she is being encouraged to remember.

Admissibility of Hypnotically Refreshed Testimony

The problems associated with hypnotically refreshed testimony have been recognized in hundreds of decisions by American courts. In 1987, the U.S. Supreme Court considered the admissibility of hypnotically refreshed testimony in Rock v. Arkansas. Following the per se exclusionary rule, the trial judge in this case determined that the hypnotically refreshed memories of the defendant were inadmissible. There was a growing trend in state courts at the time toward total exclusion of hypnotically refreshed testimony. In Rock v. Arkansas, the Supreme Court acknowledged that the possibility for contamination of the witness’s memory increases significantly when attempts are made to hypnotically refresh the witness’s memory; however, the court determined that the per se exclusionary rule cannot be applied if in doing so a defendant is denied his or her constitutional right to testify. State courts that have to deal with this kind of testimony generally recognize the problems associated with it and often apply the per se exclusionary rule to the hypnotically refreshed testimony of wit-nesses other than the defendant. Those courts that do not follow the per se exclusionary rule are usually willing to allow hypnotically refreshed testimony only if certain safeguards have been adhered to in the conduct of the hypnotic interview.

Theories of Hypnosis

A number of different theories have been proposed regarding the nature of the hypnotic experience and its relation to the behavior of the hypnotized subject. There are several characteristics of the hypnotic state that distinguish it from the normal waking state. Ernest Hilgard has proposed the following list: increased suggestibility, enhanced imagery and imagination, subsidence of the planning function, and reduction in reality testing. Hilgard contends that hypnotic phenomena often reflect a split in consciousness. It appears that the experience of the hypnotized subject is dissociated from the subsystems of control that are regulating the subject’s perceptions and behavior. The major alternative to this point of view is sociocognitive theory. The emphasis in sociocognitive theory is on the social psychological relationship between the hypnotist and the subject. According to this theory, there is no need to propose that the subject has entered into some kind of trance state or that some kind of split in consciousness has occurred;

the hypnotized subject is engaged in the performance of a role in a social situation that is largely under the control of the hypnotist. Hilgard acknowledges the fundamental importance of the social psychological aspect of hypnotic phenomena, but he contends that changes in consciousness occur when a subject is hypnotized that cannot be accounted for by efforts on the part of a compliant subject to please the hypnotist. In their theory of dissociated control, Erik Woody and Kenneth Bowers propose that hypnotized subjects are in a state temporarily like that of patients with frontal lobe damage. According to their theory, the perceptions and behavior of the hypnotized subject are under the regulation of lower-level subconscious systems that are not being monitored by the frontal lobe executive.

If hypnotized subjects process information primarily at a subconscious level, then the kinds of rules that are applied in the evaluation of information by hypnotized subjects are likely to be very different from those applied in the conscious rational analysis of information. Seymour Epstein has provided considerable support for the idea that much of the information processing that occurs in our everyday lives consists of rapid evaluations of environmental stimuli that depend largely on subconscious schemata associated with emotionally significant past events. What we might have with hypnosis is an exaggeration of this aspect of normal experience. If the subconscious experiential system dominates information processing during hypnosis, then what may occur is not that missing material gets dragged up from the unconscious to fill in the gaps in memory but that the gaps in memory are filled in with plausible information that is suggested either directly or indirectly during the hypnotic interview. It turns out that hypnosis tends to produce this kind of effect whenever the subject is required to produce a narrative reconstruction of a highly emotional event. In studies that employ stimuli of low emotional impact, hypnosis does not produce an increase in the amount of information recalled. Furthermore, it is with free recall that we see the effect of hypnosis on the amount of information recalled; when specific questions are asked or when the subject is asked to decide between various alternatives, responses are restricted so that the tendency to produce more is not revealed.

Research Findings

Some individuals are more susceptible to hypnosis than others, and there has been a good deal of research devoted to the investigation of the individual differences involved. Subjects who score high on tests of hypnotic susceptibility are generally more suggestible than those who are not very susceptible to hypnosis. Hypnotically susceptible individuals have also been found to have greater capacity for sustained attentional focus; they process information more rapidly and more easily, and they have a more active imagination and a more active fantasy life. It appears that the experiential system is particularly active in individuals who are highly susceptible to hypnosis. Subjects who are high in susceptibility to hypnosis appear to be particularly prone to accept misleading information, especially when the hypnotic interview is conducted by a trained hypnotist. Disturbingly, this is the situation where the greatest inflation of the subject’s confidence in the accuracy of his or her memory is likely to occur also.

Subjects who are highly susceptible to hypnosis can be easily led to construct vivid and detailed false memories of childhood experiences in situations that are analogs to the clinical interview when various memory-enhancing techniques are used, including hypnosis, guided mnemonic restructuring, and visualization instructions. These kinds of results are particularly relevant to the courtroom battles based on repressed memories of childhood sexual abuse. Studies of hypnotic age regression show that hypnosis and other memory-enhancing techniques can produce fantastic memories of fictional events, such as vivid and detailed memories of the hospital environment the day after birth. Michael Nash and his colleagues were able to hypnotically age regress hypnotically susceptible subjects back to an event that allegedly occurred when they were 3 years old. The instructions that were used produced memories in the majority of subjects of a transitional object, such as a teddy bear, which when checked against the memory of the mother often turned out to be false. Subjects continued to believe in these false memories when they were questioned about them subsequently in a normal waking state. Thus, vivid and detailed memories of childhood events that never actually occurred can be produced with hypnotic age regression; however, Nash found that it does not appear that hypnotized subjects in these studies are transformed to a childlike state of mind.

The degree to which sexual trauma during childhood interferes with the victim’s memory of the event or series of events is not a question that lends itself to experimental analysis. Even with the more general question of the effects of arousal on the memory of a witness, there are limits to the degree of stress that the subjects in our experiments may be exposed to. When staged events are used to examine the effect of high levels of arousal on a witness’s memory of the perpetrator of a crime, it is generally found that arousal has a debilitating effect. During emotional events, the attention of the witness is often focused on those aspects of the environment that have the greatest significance for his or her well-being, such as a weapon used by the perpetrator in the commission of a crime. The evidence suggests that due to poorer encoding of target features during these kinds of events, the witness’s ability to recognize the target in a subsequent lineup will be impaired.

When hypnosis is used to refresh a witness’s memory of an emotional event, pressure is placed on the witness to remember aspects of the event that were not initially processed very well, if at all. Research has found that hypnotized witnesses do not perform any better on photographic lineups than witnesses who have not been hypnotized. Instead, the hypnotized witness may become particularly susceptible to cues that direct attentional focus to a particular individual in the lineup, leading in some cases to misidentification of an innocent suspect. Staged-event studies have also revealed that the level of anxiety experienced by a witness during a staged event is negatively correlated with the degree of confidence subsequently expressed by the witness in a decision he or she has made about the presence of the perpetrator in a lineup. This finding has important implications regarding the cohesiveness of memories of highly emotional incidents. Regardless of the actual accuracy of a witness’s recollection of a stressful event, if he or she is less confident about it, then there is an increase in the probability that misinformation will be incorporated into the witness’s recollection of the event when he or she is questioned about it. Several studies on the effects of hypnosis on memory have produced results consistent with this hypothesis. After exposure to emotionally arousing stimuli, subjects with high levels of hypnotic susceptibility showed an increased tendency to fill in the gaps in their memories while under hypnosis, taking information suggested by the hypnotist or confabulating on their own.


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Return to the overview of Eyewitness Memory in Forensic Psychology.