Benjamin Bestgen: Twenty-first century lie detection – part two



Benjamin Bestgen

In part two of his primer on lie-detection, Benjamin Bestgen tells us what actually works. See part one here.

Psychologist Aldert Vrij, a specialist on lies and deceit, identifies viable lie detection options which do not involve technology, torture or chemicals. Looking at lying clinically, he finds that:

  • lying may be cognitively more demanding as the liar may have to plan the lie – anticipate possible questions, fabricate plausible information, remember what he told to whom and maintain his story consistently;
  • liars make conscious efforts to appear credible by monitoring their behaviour and speech to appear honest, which is cognitively demanding too;
  • liars invest more energy into observing the reactions of the person they lie to, ascertaining whether they are being believed;
  • liars may have to roleplay their lie and at the same time suppress the truth, which requires further mental resources; and
  • lying is generally more intentional and deliberate, which again needs extra attention compared to truth-telling, which is more automatic.

Based on this, Vrij and fellow researchers found that certain interview and communication techniques can increase the probability of spotting lies accurately.

Increase cognitive load: making additional requests might strain the mental resources of a liar more than for a truth-teller. Asking a liar to tell his story in reverse order runs counter the natural “forward” order of narrating events and also disrupts any rehearsed schema the liar has prepared. Demanding to maintain eye contact with the interviewer further taxes mental resources, because it is distracting when we try to concentrate on telling our story. This method indicated a lie detection success of 60 per cent, slightly better than our “natural” abilities.

Drawing and asking strategic questions liars do not expect: a person pretending to have met somebody else at a restaurant might struggle to answer questions about the interior or how far away they sat from the bar. The suspect can also be asked to draw the layout of the restaurant and include the position of specific objects like an aquarium or sculpture in it. Drawing prevents the liar from beating around the bush verbally. Drawings of liars will generally be less detailed and prone to omitting things truth-tellers can readily recall. The drawing request can also discourage a liar from maintaining his lie, as the liar may feel it’s too risky or impossible to comply with the request convincingly.

Play devil’s advocate: when trying to uncover if a person is lying about beliefs they claim to hold, asking “devil’s advocate” questions can help to discover what somebody really thinks. First, a person is asked a question inviting them to argue in favour of what they claim to think. Secondly, the person will be then asked to argue for the reverse position, in a “Playing devil’s advocate here, could you say anything against…”? style.

People tend to think more deeply about and provide more reasons for beliefs they support, so the response to the question about their favoured perspective is likely to be longer and more detailed. A truthteller will struggle more to argue against her favoured view and be shorter and more general in her response to the “devil’s advocate” question. A liar likely shows little difference in length or detail to either question: he will rehearse his detailed lie in the first question but also find it easy to argue at length and in detail the “devil’s advocate” question which may be closer to what he actually believes.

In experiments comparing the responses of people to this style of questioning, 75 per cent of truth-tellers and 78 per cent of liars were identified correctly.

Strategic use of evidence (SUE): police and, to a degree, lawyers and journalists will be familiar with the SUE technique. When being questioned, a guilty suspect is concerned about interviewers not learning the truth while an innocent person usually wants to tell everything as it happened. A truthteller will likely be forthcoming while a liar will use avoidance strategies and denials.

Armed with whatever evidence they have, the interviewers will not reveal their knowledge but use it as background to ask questions a liar will struggle to answer. Questioning may start with an open question “What did you do on Sunday 14 June in the afternoon?”, followed by a specific one: “Did you or anyone else drive your car on that Sunday afternoon?” (Interviewers will not disclose that they have CCTV showing the suspect’s car being driven on that date and time).

Truthtellers will usually mention the car being driven either spontaneously or after being prompted (“Tell it like it happened, please.”). Liars are more likely to avoid mentioning the car spontaneously or will utilise denial or deflection strategies when prompted, which may contradict the evidence.

Tests on the usefulness of SUE showed that SUE-trained interviewers spotted lies with 85.4 per cent accuracy, while untrained interviewers only managed 56.1 per cent.

The above indicates that with some preparation, interview skills and thought, liars can be spotted with greater accuracy and no need for any particular technology. Skilled advocates and interrogators will no doubt utilise these or similar techniques in their work already.

But for those of us hoping to get better at catching our colleagues, family or friends in their lies, we should consider that most of us would probably feel aggrieved being subjected to cross-examination, structured interviews or being asked to draw where we’ve been on a specific date. Therefore, maybe we should restrict concerted efforts at lie-detection to areas in life where it really, truly matters and otherwise take a more indulgent view on the foibles that make all of us economical with the truth sometimes?

Benjamin Bestgen is a solicitor and notary public (qualified in Scotland). He also holds a Master of Arts degree in philosophy and tutored in practical philosophy and jurisprudence at the Goethe Universität Frankfurt am Main and the University of Edinburgh.



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