How to spot a liar

This new method is effective and ethical

Cody Porter, University of Portsmouth

Guilty? The length of your answer may give it away. 
Motortion Films/Shutterstock

Most people lie occasionally. The lies are often trivial and essentially inconsequential – such as pretending to like a tasteless gift. 

But in other contexts, deception is more serious and can have harmful effects on criminal justice. From a societal perspective, such lying is better detected than ignored and tolerated.

Unfortunately, it is difficult to detect lies accurately. Lie detectors, such as polygraphs, which work by measuring the level of anxiety in a subject while they answer questions, are considered “theoretically weak” and of dubious reliability. 

This is because, as any traveler who has been questioned by customs officials knows, it’s possible to be anxious without being guilty.

We have developed a new approach to spot liars based on interviewing technique and psychological manipulation, with results just published in the Journal of Applied Research in Memory and Cognition.

Our technique is part of a new generation of cognitive-based lie-detection methods that are being increasingly researched and developed. These approaches postulate that the mental and strategic processes adopted by truth-tellers during interviews differ significantly from those of liars. By using specific techniques, these differences can be amplified and detected.

One such approach is the Asymmetric Information Management (AIM) technique. At its core, it is designed to provide suspects with a clear means to demonstrate their innocence or guilt to investigators by providing detailed information. 

Small details are the lifeblood of forensic investigations and can provide investigators with facts to check and witnesses to question. Importantly, longer, more detailed statements typically contain more clues to a deception than short statements.

Essentially, the AIM method involves informing suspects of these facts. Specifically, interviewers make it clear to interviewees that if they provide longer, more detailed statements about the event of interest, then the investigator will be better able to detect if they are telling the truth or lying. For truth-tellers, this is good news. For liars, this is less good news.

Indeed, research shows that when suspects are provided with these instructions, they behave differently depending on whether they are telling the truth or not. Truth-tellers typically seek to demonstrate their innocence and commonly provide more detailed information in response to such instructions.

In contrast, liars wish to conceal their guilt. This means they are more likely to strategically withhold information in response to the AIM instructions. Their (totally correct) assumption here is that providing more information will make it easier for the investigator to detect their lie, so instead, they provide less information.

Liars tend to withhold information. Photographee.eu/Shutterstock

This asymmetry in responses from liars and truth-tellers - from which the AIM technique derives its name - suggests two conclusions. 

When using the AIM instructions, if the investigator is presented with a potential suspect who is providing lots of detailed information, they are likely to be telling the truth. 

In contrast, if the potential suspect is lying then the investigator would typically be presented with shorter statements.

The experiment

But how effective is this approach? Preliminary research on the AIM technique has been promising. For our study, we recruited 104 people who were sent on one of two covert missions to different locations in a university to retrieve and/or deposit intelligence material.

All interviewees were then told there had been a data breach in their absence. They were, therefore, a suspect and faced an interview with an independent analyst. Half were told to tell the truth about their mission to convince the interviewer of their innocence. 

The other half were told that they could not disclose any information about their mission, and that they should come up with a cover story about where they had been at the time and place of the breach to convince the analyst of their innocence.

They were then interviewed, and the AIM technique was used in half of the cases. We found that when the AIM technique was used, it was easier for the interviewer to spot liars. In fact, lie-detection accuracy rates increased from 48% (no AIM) to 81% – with truth-tellers providing more information.

Research is also exploring methods for enhancing the AIM technique using cues which may support truth-tellers to provide even more information. Recalling information can be difficult, and truth-tellers often struggle with their recall.

Memory tools known as “mnemonics” may be able to enhance this process. For example, if a witness of a robbery has provided an initial statement and cannot recall additional information, investigators could use a “change perspective” mnemonic – asking the witness to think about the events from the perspective of someone else (“what would a police officer have seen if they were there”). This can elicit new - previously unreported - information from memory.

If this is the case, our new technique could become even more accurate at being able to detect verbal differences between truth-tellers and liars.

Either way, our method is an ethical, non-accusatory and information-gathering approach to interviewing. The AIM instructions are simple to understand, easy to implement and appear promising. While initially tested for use in police suspect interviews, such instructions could be implemented in a variety of settings, such as insurance-claim settings.

Cody Porter, Senior Teaching Fellow in Psychology and Offending Behaviour, University of Portsmouth

This article is republished from The Conversation under a Creative Commons license. Read the original article.