This paper examines the use of hypnosis in criminal investigations, commonly referred to as forensic hypnosis. It begins by defining hypnosis as understood by the American Psychological Association and explains how hypnotic suggestion is intended to recover forgotten or repressed memories in witnesses. The paper then critically evaluates three major problems associated with forensic hypnosis: the decline in memory accuracy accompanied by confabulation, heightened suggestibility to leading questions, and unwarranted increases in subject confidence regardless of factual accuracy. Drawing on psychological research, the paper concludes that these combined limitations render hypnotically obtained testimony unreliable and argues that its use in legal investigations should be prohibited, with hypnosis restricted to clinical therapeutic contexts.
Before discussing hypnosis in investigation, it is important to understand what the term means. The American Psychological Association (1994) defines hypnosis as "an interaction between one person, the 'hypnotist', and another person or people, the 'subject' or 'subjects'." In this process, the subjects' perceptions, feelings, thinking, and behavior are influenced by the hypnotist. This is achieved by asking the subject to concentrate on ideas and images that may induce the intended effects. The hypnotist uses "suggestions" to bring about these effects; what distinguishes these suggestions from ordinary daily instructions is that their success is measured by a state of involuntariness or effortlessness in the subject.
Hypnosis has been applied in various fields, including crime investigations, in which context it is referred to as forensic hypnosis. The main aim of forensic hypnosis is to bring into memory, for a witness, events or details that they may have forgotten or repressed. It is the nature of human beings to forget less important details of their environment; even important things are sometimes forgotten, especially when they tend to disturb or traumatize the person. However, the general belief is that almost everything a person sees, hears, and experiences is stored somewhere in the mind, and that these memories can be retrieved through heightened awareness — which is the stated purpose of hypnosis.
Even though hypnosis has been widely employed in investigations, there are significant problems associated with the process. The primary intention of hypnosis is to increase correct memory recall; however, it has been associated with a very significant rise in incorrect memory — that is, the accuracy of recall declines (Lynn and Sherman, 2000). One way of evoking memory is by activating visual memories from the past and heightening the ability to fantasize. When the subject is in such a state, there is a tendency to accept events suggested by the hypnotist even if they never actually occurred. This is especially likely when reality is persistently distorted during the session.
The decline in accuracy may not be detected easily because it is often accompanied by finer detail. Whenever a person gives vague details about an event, their memory is likely to be doubted; however, when the details are specific, people tend to believe the information is accurate. Hypnotized individuals can apparently recall events with perfect detail and verisimilitude. The problem is that this detailed recall can be the result of confabulation — simply put, memory distortion. In short, hypnosis can cause individuals to lose the ability to differentiate between what they think happened and what actually happened. This problem can be reduced by ensuring that reality is not distorted during the session; the hypnotist should present situations as accurately as possible and work to maintain the integrity of information derived from the subject.
"Subjects adopt hypnotist suggestions, distorting accounts"
"Subjects grow confident in inaccurate false memories"
Taking into consideration the problems associated with hypnosis, it should not be used in investigations, as information obtained through hypnosis cannot be considered reliable. The law should therefore require the exclusion of testimony obtained from previously hypnotized witnesses; as a practical matter, such a witness has been rendered incompetent to testify reliably. Legal standards around the admissibility of evidence exist precisely to protect the integrity of proceedings, and hypnotically influenced testimony poses a clear threat to that integrity. Hypnosis should be restricted to clinical use, where the goal is a desired therapeutic change in a patient — a context in which its limitations are less likely to cause injustice.
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