Forensic hypnosis: Royal road or dead end on the way to eyewitnesses’ memories?

Hypnosis seems to be the solution to a multitude of problems: it is used as an aid to quit smoking, to lose weight, and police officers enthuse over its miraculous effects on eyewitness memories. How does eyewitness research explain the latter phenomenon?

Let’s take a look at a case in which hypnosis played a key role: In 1982, Larry Mayes was charged with rape and sentenced to 80 years in prison. The hypnotized victim had identified him from a lineup and was highly confident about her decision. File closed – until in 2001, after 19 years of imprisonment, Mayes was exonerated due to exculpatory evidence. It turned out that the victim had not been able to identify him from two preceding lineups. Only in the third procedure, after being hypnotized, did the victim identify Mayes as the perpetrator. He was eventually exonerated by forensic analyses showing that the DNA found at the crime scene did not match his.

Although one might be inclined to consider this case an exceptional tragic incident not worth of further attention, this seems unlikely. Hypnosis can significantly elevate error levels in eyewitness accounts and can even make witnesses develop vivid, but completely false memories of entire past events, so called pseudomemories. To make things worse, hypnosis leads to confidence inflation. This means that hypnotized witnesses are more confident in their accounts than non-hypnotized witnesses, even when making errors, which entails the danger that hypnotized witnesses are by mistake regarded as highly credible. The errors emerge, because it is difficult to distinguish actually experienced from imagined events when hypnotized. This is why hypnosis is not a suitable tool for interviewing eyewitnesses. Why is it, then, that hypnosis is still enjoying great popularity among some police forces? The procedure is frequently used in stagnating cases or in cases in which witnesses remember only little. Under hypnosis, the report criterion of eyewitnesses drops. Consequently, they report more details – but also make more errors. Because the police do not possess objectively true information about the incident, they get the impression that hypnosis helps them achieve their goal, to wit, more detailed reports. In laboratory experiments, however, it becomes apparent that many details reported under hypnosis are simply false.

In conclusion, we can rightly consider hypnosis a dead end when it comes to accessing eyewitnesses’ memories. Well-developed and -researched interview techniques, such as the Cognitive Interview, elicit comprehensive accounts, without bearing the danger of false memories as a result of increased suggestibility. This is what one may call the royal road to eyewitnesses’ memories.

References:
http://www.innocenceproject.org/Content/Larry_Mayes.php

Kebbell, M. R., & Wagstaff, G. F. (1998). Hypnotic interviewing: The best way to interview eyewitnesses? Behavioral Sciences and the Law, 16, 115-129. doi:10.1002/(SICI)1099-0798(199824)16:13.0.CO;2-I

Written by Alana C. Krix and Melanie Sauerland, this blog was originally published in German at de.in-mind.org.

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