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Detecting deception

In the process of investigation very often police has to face the challenge of revealing the deception. It is highly probable that suspects and even witnesses lie during interviews, so the police and criminal psychologists need to be capable of detecting deception.

There are some common beliefs about the cues to lying. For example everyone thinks that when a person lies they will look in the eye less. Also they have more gestures, shift the body position often and move their hands more. But actually these cues relate more to nervousness. If a person is nervous they may behave like this, but it does not necessarily mean that the lie is detected. Very often, when for example an innocent witness is nervous, they act like this. On the other hand an offender can be very calm while being interviewed, they may have taken time to prepare their lies and don’t show any of the suspicious gestures or signs. It means we have to be very careful to tell the nervousness signs from a lie signs.

Another important point is that, since there are some common and agreed signs, that people believe are indicating lying, liars will, of course use this and don’t behave in the way people are expecting them to behave when they lie. It means that an intelligent liar, with relatively high IQ will never give you a chance to spot the deception by their behavior or gestures.

And how do people behave while lying after all? An overview of a lot of studies about it showed that actually there are no highly reliable behavioral signs of deception.  And if so, than how do professionals detect deceptions?

The recent studies in the US and UK show that professionals (e.g. police officers) are also not so good at detecting a lie, the average rate of success in the experiments are about 60%, that is only 10% more than a chance. One possible explanation of this low rate is, of course, that in experimental situations people don’t have so strong emotions and they don’t show as much cues as in the real life situations when skates are much higher.

How can their work efficiency be improved?

First of all, the stereotypes must be removed. Researches also showed that people who have some beliefs about the cues to lying prior to the interview are worse at detecting a lie. For example, many people think that honest and attractive-looking people always lie less, or that people who are nervous lie more (when they might be just introverted or unsocial).  They need proper trainings about how to conduct an information gathering investigative interviews. Training should be focused on:

  • Myth dissolution (that the common beliefs about cues to lying are usually wrong).
  • Information about some cues that studies showed in some cases (but not always) indicate lying.
  • Feedback on how accurate they were in making “lie or not” decisions.

Another method of detecting deception is so called RM (reality monitoring) approach. It focuses on the speech content instead of behavioral cues. The approach is based on the assumption that the memories about the experienced events (true) are different from the memories based of imagining (lie). While saying the truth perceptual processes are involved and the speech includes contextual (space, time), sensory (shapes, colours), and auditory (speech) information. Studies showed that average accuracy of this approach is about 70% (20% more than a chance). Of course this number is still far below perfection but it is much more effective than 60% of considering only behavioural cues.

As a resume, we can say that there are no perfectly reliable methods for detecting deception. Some improvements can be made with trainings and involvement of psychologists, but probably the accuracy of detecting a lie mainly depends on the experience of the police officer.

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