Forensic hypnosis

Posted by on Wednesday 5th November 2003. 3 comments.

Hypnosis is basically ‘self hypnosis’. If you ware watching an engaging film you convince yourself its plausible – you suspend your disbelief.

People who believe they are hypnotised have access to their unconscious minds, which is irrational so they are more suggestible i.e. believing they are a chicken.

Explicit memory may hold the information that is needed by the interrogator. Dissocialise amnesia is when for example you are in a car crash and you may not be able to recall the events before, during and after the crash. But explicit memories may be intact and being hypnotised may release this knowledge. The hypnotist is a guide.

Hypnosis is good at getting evidence from a crime scene or the scene that they may not remember. The re-create the scene to help with recall.

Martin Reisser first used this in the 70’s. He claims that hypnosis can produce recall with 90% accuracy. Critics such as Orne, urges caution when considering evidence from hypnotised witnesses and recollections can be distorted.

Hypnosis depends on the unconscious mind and is highly suggestible as the unconscious mind lacks reality – like flying. An example is the “Hillside strangler case” when 10 women were murdered and a suspect was arrested but he denied it. Under hypnosis he demonstrated the symptoms of multiple personality disorder – individual personalities co-exist within the same body. The was an alter ego – he had 5 of them. His lawyers claimed that the “ken personality” (his name was ken), knew nothing about the other personalities so he couldn’t be charged, - they claimed he was not guilty due to insanity. The hypnotists backed up the claim, but Orne found that under hypnosis he acted in a ways that was inconsistent with someone who is actually hypnotised – so Orne concluded he had faked hypnosis – and after this the suspect pleased guilty.

Hypnosis of witnesses and victims
In 1989 Reisser reviewed studies of the effectiveness of hypnosis:
One needs to take account of the meaningfulness an emotional impact of certain cases
One needs to take into account retrieval cues – some studies used real interviews and some didn’t.
In some studies there was no cross examination of some of the witnesses.

Geiselman and Machlovitz (1987) reviewed 38 experiments from 30 different hypnosis studies. Found that 21 were more effective, 13 showed no effect and 4 of them impaired the recall. When looking at the techniques identified 3 factors that appear to facilitate hypnotic recall are:

1) An interactive recall
2) Longer Delay – hypnosis is more effective over longer periods
3) If the material contains realistic and emotionally provocative material then its likely to be driven by emotion in the unconscious mind

Stebley and Boothwell (1994) reviewed 19 studies, 3 facilitated the recall, 5 had a bad effect and 11 had no effect at all. But hypnosis was more effective when the delay was over 24 hours. Recognition is used in things such as line-ups – by hypnosis doesn’t help at all in this situation.

Few courts admit hypnotically obtained evidence. However it has been used to direct and guide criminal investigations and forensic psychologists have developed guidelines for the use of hypnosis:

1) Hypnotic induction should only be inducted by trained psychologists and psychiatrists
2) Pre-hypnosis reports are needed as a baseline to compare recall rates.
3) The whole thing is videotaped to make sure hypnotists don’t influence the witnesses (using NVC etc)
4) Hypnotisability is measured before the test
5) A pre-hypnosis briefing is carried out BEFORE hypnosis for ethical reasons as many people already have poor preconceptions about hypnosis
6) New facts should not be introduced during the hypnotic session
7) Hypnosis should NEVER replace standard investigative procedures. It’s a supplement

The general consensus is that hypnosis is not a reliable technique in this context and the evidence it does facilitate is tenuous.

So the cognitive interview technique is used nowadays and it uses context re-instatement. – Mentally re-creating the event and the scene. This approach exploits ESP (encoding specificity principle) and was developed by Tulving.
The likelihood of someone remembering something is improved when the initial cues are present. So re-creating it should bring the cues back. It does this because memory is associative. It links things together.
Witnesses are asked to not only recall things about the crime, but also trivial things in the cognitive interview. They are also asked to recreate emotions, and report the events from the vie of another witness in the hope to find and associative event. Studies have shown that the cognitive interview technique can be effective.

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