Psychology
'Smart' liars caught out by researchers
Tue, 04 Dec 2012 13:04:00 GMT
Researchers at the University of Portsmouth may have found a way to catch out liars who pass an established lie detection test.
It is the first experiment to reveal a pattern in how guilty people approach what’s known as a Symptom Validity Test.
The test is a clinical assessment tool used by neuro-psychologists to determine if someone’s claims of amnesia are genuine, and it bears no resemblance to better known lie detection tests, such as the polygraph. The researchers adapted the test to see whether participants would incriminate themselves by avoiding guilty knowledge.
In the experiment 86 people were asked to commit a mock crime by stealing a data in the form of a PDF named ‘delta’, from a computer with a distinct yellow background.
A further 82 people allocated to the control group had no knowledge of the crime. All were then submitted to a lie detection test that looks for signs that someone is avoiding associating themselves with anything directly related to the ‘crime’.
The Symptom Validity Test requires people to choose one word from a pair of words. Each pair contains a word relating to the crime and a neutral word not related to the crime. In this experiment, crime-related words included ‘PDF’, ‘delta’ and ‘yellow’ and neutral words included ‘JPEG’, ‘bravo’ and ‘red’.
In the test, innocent people with no knowledge of the crime chose an equal number of crime-related and neutral words.
Liars, on the other hand, chose the crime-related words just 33 per cent of the time and 40 per cent scored below chance and failed the test after choosing three or fewer crime-related words.
If someone fails the test, it is a strong indication of guilt. However, the researchers caution that passing the test does not indicate innocence, and it is possible to beat the test by using a strategy.
Researcher Dom Shaw said: “What is unique about this study is that we found a pattern in the guilty participants’ responses.
“Our results suggest that at some point during the test, some liars worked out that avoiding too many crime-related words would appear suspicious. As a result, they started including more crime-related words to appear as if they were choosing purely by chance.”
Some guilty participants who beat the test tended to avoid the crime-related words at the beginning, but then included some later on, indicating they understood how the test works and that avoiding the guilty knowledge too often will appear deceptive.
These ‘smart’ liars may have passed the test when looking at their overall scores, but they still left evidence of their guilt in their pattern of responses, said Mr Shaw, and this information might increase the value of the test because passing it in this way might indicate guilt.
After the experiment, participants were asked what strategies they had used to answer the test. The two most popular strategies cited by the liars were to deliberately select some correct answers and attempt to randomise their answers. Of those who expressed some understanding of how the test works, a third still failed.
Mr Shaw said: “Some liars may have grasped how the test works too late, meaning they simply didn’t have enough time to perform at chance level.
“One other explanation is that deceptive participants simply struggled to answer randomly. While it is not clear exactly why this might be the case, there is some suggestion that humans struggle to make random responses.”
The researchers suggested that a test containing more than 12 questions might reveal more about the liars’ deceptive response patterns.
Mr Shaw said: “With a longer Symptom Validity Test we might see liars switching back and forth between selecting each type of word for a period of time. In their attempts to answer randomly, liars may in fact incriminate themselves.”
The researchers said that while the findings are encouraging, the results need to be treated with caution.
Mr Shaw said: “The test shows promise in detecting feigned crime amnesia. Our findings should be treated as a foundation, and future research is needed.
To further explore the value of the findings, the next step for the researchers is to examine data from those who have been coached to beat the test.
Mr Shaw said: “Our participants were not told how they could beat the test, but in real life, barristers may coach their clients about how to pass neurological tests. The next challenge is to examine the response patterns of those who have been coached to see if this reveals similar evidence of deception.”
The research is published in Legal and Criminological Psychology.