This paper evaluates the use of hypnotic testimony in legal proceedings, focusing on the scientific limitations of hypnosis as a memory-enhancement tool and the resulting legal challenges. Drawing on research by Orne, Kebbell, and Wagstaff, the paper discusses how hypnosis can simultaneously increase both correct and incorrect recall, render subjects vulnerable to suggestion, generate false confidence, and fail to prevent deliberate deception. It surveys the divergent legal approaches courts have adopted toward pretrial hypnosis, from absolute exclusion to jury-based weight determinations and constitutional due process scrutiny. The paper concludes by introducing the cognitive interview as a scientifically validated alternative that captures the recall benefits of hypnosis without its memory-distorting dangers.
The use of hypnotic testimony in court is an appealing idea, mainly because of the layperson's perception of the strengths of hypnosis. However, research clearly demonstrates that there are several weaknesses associated with hypnotic interviews, which can impair the credibility of a witness who is later asked to testify on the stand. These weaknesses include decreases in accuracy, vulnerability to hypnotic suggestion, false confidence with regard to incorrect answers, vulnerability to leading questions, and the facts that people can fake hypnotic states and lie even while under hypnosis. Therefore, courts have greatly limited the circumstances under which hypnotic testimony can be introduced. Despite these weaknesses, interviewers can obtain helpful information when a witness is hypnotized. For this reason, some researchers have suggested using cognitive interviews, which offer many of the same memory-recall benefits as hypnotic interviews without introducing the same dangers of memory impairment.
It is important to understand the limitations of hypnosis. "Laymen often think of hypnosis as an infallible and extremely powerful memory aid, but research has shown that this notion is not correct" (R.T.C., p. 1208). The scientific community has established that a person cannot access all of his or her own memories, regardless of hypnotic state. Memory simply does not contain every event that has ever occurred in a person's lifetime (R.T.C., p. 1209). In fact, for certain types of events, memories recalled under hypnosis are no better and no worse than regular memories (R.T.C., p. 1209).
After examining a substantial body of research, Kebbell and Wagstaff determined that hypnosis is helpful in getting witnesses to recall information (p. 118). The problem is that some research shows that hypnosis increases both incorrect and correct memories (Kebbell and Wagstaff, p. 118). Furthermore, when placed in a forced-choice scenario — rather than being permitted to give free-form responses about what occurred — hypnosis increases incorrect reporting (Kebbell and Wagstaff, p. 118).
While the fact that hypnosis increases both incorrect and correct responses suggests that it does not impair overall accuracy, it also means that hypnosis does not increase overall accuracy, either. Furthermore, since subjects under hypnosis "will not carry out activities which are morally unacceptable or inherently self-destructive… hypnosis should not cause a guilty individual to confess to a crime, since it is rarely if ever advantageous for a defendant to confess" (Orne, p. 66).
It is also important to recall that hypnosis does not change a person's basic nature or motivational structure, which can complicate the determination of the truth or falsity of the facts recalled. "When hypnosis is used with a defendant or plaintiff who has much to gain by recalling one set of memories rather than another, motivational factors are superimposed upon the basic mechanisms involved in hypnotically aided recall" (Orne, p. 68). Furthermore, when subjects are asked specific questions or given specific instructions, there is a modest increase in memory but also a tendency to fill in those aspects that cannot be remembered (Orne, p. 74). The same process that makes subjects vulnerable to hypnotic suggestion "makes it possible for subjects to accept approximations of memory as accurate" (Orne, p. 74).
Hypnotized subjects frequently display a false confidence in their "remembered" information. "The most consistent confidence effects emerge when misleading information is introduced subtly into a situation well before testing" (Kebbell and Wagstaff, p. 119). While hypnosis does not appear to increase a subject's susceptibility to suggestion by leading questions, it also does not reduce that susceptibility (Kebbell and Wagstaff, pp. 119–120). The confidence issue becomes especially significant when one considers how fact-finders judge eyewitness testimony; confidence plays an important role in whether juries believe a witness's account (Kebbell and Wagstaff, p. 121).
More importantly, one must recognize that it is impossible to rule out the possibility that people under hypnosis are deliberately lying about events they have perceived. "It is asserted frequently that hypnotized people always tell the truth, even though scientific studies do not support this statement. Scientific data notwithstanding, the popular media have reported these misconceptions" (R.T.C., p. 1209). Courts have recognized that hypnotic testimony does not exclude the possibility of willful falseness (Orne, p. 63). This is a critical distinction, and it builds upon other research indicating that hypnosis does not guarantee the accurate recall of memories. Even highly experienced hypnotists can be fooled as to whether a subject has actually been hypnotized (Orne, p. 64), and even deeply hypnotized subjects are able to lie willfully (Orne, p. 64).
Hypnotized individuals can also be very susceptible to suggestion more broadly. A hypnotized individual may be unable to critically judge the veracity of his or her own recollections (R.T.C., p. 1212). Furthermore, "because hypnotized persons are highly suggestible, some authorities believe that they can easily be induced to embellish or alter their memories of events" (R.T.C., p. 1212).
While this tendency may produce only harmless investigative leads in the course of a police investigation, it can have dire consequences as well. For example, the tendency toward suggestible confabulation has led to false confessions when non-suspect witnesses have been interrogated about crimes they witnessed (Orne, p. 67). Hypnosis can be helpful during an investigation because the risk of introducing incorrect information is more permissible at that stage — the investigation should be able to sort truthful information from incorrect information. However, courts are wary of witnesses who have been hypnotized prior to testifying. "Indeed, most prosecutors recognize that if they hypnotize a witness who later turns out to be implicated as a defendant, they will significantly complicate his or her ultimate prosecution" (Orne, p. 67).
The suggestion does not even need to be overt. "The content of pseudo-memories, when they are wittingly or unwittingly induced during hypnosis, is not random… if a witness is hypnotized and has factual information… many of these bits of knowledge will become incorporated and form the basis of any pseudo-memories that develop" (Orne, p. 78). This can be understood through memory theory, which holds that memory is reconstructive — that the process of remembering "is thought to involve reconstructing events based on fragments of experience" (R.T.C., p. 1213). "The reconstructive theory raises the possibility that an erroneous recollection of an event may permanently alter the memory of the event and destroy the original accurate information" (R.T.C., p. 1213).
"Courts take divergent approaches to pretrial hypnosis"
"Cognitive interview improves recall without memory distortion"
Kebbell, Mark and Graham Wagstaff. "Hypnotic Interviewing: The Best Way to Interview Eyewitnesses?" Behavioral Sciences and the Law 16 (1998): 115–129.
Orne, Martin. "The Use and Misuse of Hypnosis in Court." Crime and Justice 3 (1981): 61–104.
R.T.C. "The Admissibility of Testimony Influenced by Hypnosis." Virginia Law Review 67(6).
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