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There is no tell-tale, sure-fire, absolutely reliable sign of lying. Nothing in demeanour or physiology which is always present when someone lies and always absent when someone is truthful has yet been discovered. But that doesn’t mean it isn’t sometimes possible to do far better than chance in discerning whether a person is lying or telling the truth.
Some government agencies still believe that the polygraph is a lie detector. Changes in heart rate, respiration and sweating on the palms or fingers are recorded when the subject responds with a ‘yes’ or ‘no’ answer to a series of questions that have been explained before the test so that there will be no surprises. The hope is that the guilty suspect will show an increase in these measures of autonomic nervous system activity when asked a question relevant to the crime.
The polygraph can be useful if there are crucial facts known only to the police and the killer. Then what is called a guilty knowledge series of questions can be asked. For example, ‘Was Mrs Smith killed with a gun or a knife?’ The person who knows the answer, presumably only the killer, is more likely to show an increase in autonomic physiology when the correct answer is mentioned. But this method is not perfect, and very often there is no such information known only by the police and the perpetrator. In the more typical polygraph examination, accuracy is better than chance but there can be sizeable ‘false positives’ (innocents called guilty) and ‘false negatives’ (guilty persons called innocent). How many mistakes are made is not known; it depends on the examiner, the individual examined and various other factors.
The single biggest use of polygraph lie detectors in the United States today is in pre-employment and periodic screening for those in national security jobs. (Before such use was outlawed in private companies, fast food outlets were the biggest users, trying to weed out those who were likely to steal.) I served as a member of a panel appointed by the US National Academy of Sciences to evaluate the scientific validity of the polygraph in national security screening. Our report issued last autumn said there was no scientific evidence that it is valid for such a use.
Putting aside measurement of physiology, many people believe they can identify lies from demeanour: what is said, how it is said, gaze direction, posture, gesture and/or facial expression. There are many false clues in circulation, based upon conjecture, anecdote or imagination, and endlessly repeated in the media. One of the most popular, still taught in some American law enforcement agencies, is that whether you look to the left or right when asked a question distinguishes the liar from the truthful person. This is a fundamental tenet of what is called Neurolinguistic Programming (NLP), but tests carried out by my colleagues and myself showed it is not valid, though some people still swear by it.
Also worth taking into account is that lies are, of course, not all born of criminal motivations. There are a number of reasons why people lie: to avoid punishment; to get out of an awkward situation; to help another person; to gain a reward not obtainable at all or not as easily without lying; because of the excitement of taking a risk of being caught; and to control another person. Similarly, there are a variety of reasons why lies succeed. Often it is because the target simply doesn’t care: does the host scrutinise to see if the guests are truthful when they said they had a lovely evening?
Often the target unwittingly colludes in being misled. Neville Chamberlain wrote home to his sister the night after he met Hitler that he could tell from Hitler’s face that he meant what he said. Very often the target has a great deal to lose by catching the liar, even though the costs may be even greater later. Did Chamberlain want to discover that his policy of appeasement had been exploited by Hitler, and his country was now at serious risk? Does the employer really want to find out he hired an embezzler, any more than parents want to discover their children are using hard drugs, or a spouse wants to learn he or she is being betrayed?
Psychologically, we put off discovering the bad news even if it will get worse later; at least we don’t have to face it now. The woman at the CIA who caught Aldrich Ames, the worst spy in the history of that agency, said that when you catch a spy you have to ask yourself why you didn’t catch that person earlier. In a sense,unless you catch the spy in the beginning of his or her treachery, you have failed as a counter-spy, and that may lead you to overlook clues that could have tipped you off.
Yet there are times when we really do want to find the truth no matter what the cost. Are there clues in demeanour? Not if the lie is trivial – ‘sorry I’m on my way out the door; can’t make it next week, babysitting problems,’ and so on. Lies may be uncovered only when there is a lot to gain or lose if the lie is discovered. Then unless the person is extremely well prepared and rehearsed, there are both cognitive and emotional signs that can be helpful in evaluating a person’s truthfulness. For example, there often is an increase in hesitation and a decrease in the use of the hands to illustrate speech when someone is thinking about what they are saying as they say it. This might be creativity, inventiveness or fabrication. The interviewer needs to ask more to find out.
High-stake lies may also generate emotions that don’t fit what the person is saying: fear of being caught, guilt about lying, or what I call ‘duping delight’, may leak in the face, body or voice and suggest the person is not being truthful. But they are only what I call exploration flags. Discrepancies between what someone says and how they say it can arise for many reasons. Emotions don’t tell us their source. To avoid Othello’s error – not recognising that the fear of being disbelieved looks the same as the fear of being caught in a lie; hence convincing himself wrongly of Desdemona’s infidelity, from her reactions – we need to investigate why the person is showing an emotion that doesn’t fit what they are saying.
The training I offer to law enforcement alerts people to the most subtle signs of emotion. These are by definition very small and restricted to but one region of the face. There may be a movement, barely noticeable, in the chin, lips, cheeks, lower or upper eyelids, or brows. When these slight movements appear in this isolated way, they signal that an emotion is just beginning. The person showing the expression may not yet be aware of feeling an emotion; that may not register in consciousness for many more seconds. These subtle expressions also may occur as what I have called ‘leakage’ – all that escapes deliberate attempts to conceal any sign of what is being felt. Usually missed, once you have learnt to read facial movements, you should begin to recognise them.
Of course, I’d hope that these emotional recognition skills have more general usefulness. (Better understanding how another person is feeling at any moment can be helpful in all sorts of relationships.) For the law enforcers, however, they should sure help spot a liar.