Liars may fear polygraph tests and brain scans, but surely they wouldn't expect a simple drawing to give them away. It seems that how you draw a scene can help reveal if you really were there or just made the whole thing up.
No lie detector is anywhere near foolproof, and existing techniques, including polygraph tests and brain scans, have the added drawback of requiring specialized, expensive equipment, says Aldert Vrij, a forensic psychologist at the University of Portsmouth, UK.
Vrij wondered whether asking someone to draw a scene might work instead: as liars have not had direct visual experience of what they are describing, they might draw a scene differently to someone who was actually there.
To test the idea, his team sent 31 volunteers on a cloak-and-dagger mission in which they had to pick up a laptop computer from an actor posing as a secret agent, and deliver it to a second agent. The second agent then asked volunteers to describe how and where they had received the laptop and to sketch the location in detail. Half of the volunteers were told to answer this question with a lie and half told to tell the truth.
While many of the liars gave convincing verbal accounts to the agents, when their drawings were compared with those of truth-tellers, there were features that distinguished them.
The first was who they drew: 2 out of 16 liars included the first agent in their drawing, whereas 12 out of 15 of the truth-tellers included that detail. Vrij suggests this is because the liars visualized a place they knew and simply drew this, neglecting to include the agent.
The second difference was perspective, with liars tending to draw the laptop handover from a bird's-eye perspective rather than a first-person one. Vrij suggests that while liars are adept at quickly coming up with a plausible verbal account, they find imagining spatial relationships between conjured-up objects more difficult from a first person perspective.
He reckons asking suspects to sketch scenes could help police determine who is telling the truth.
But couldn't savvy criminals learn these giveaways and avoid them? For example, liars in the know might start taking care to include people in their drawings.
Perhaps, but Maria Hartwig, a forensic social psychologist at John Jay College of Criminal Justice in New York, who was not involved in the new study, points out that liars might be reluctant to add people as they might trigger further questions from police.
Researchers have yet to test the method on larger groups of volunteers to work out how often it mistakenly flags up as liars people who are telling the truth.
However, some police already do something similar. The Denver Police Department in Colorado has electronic white boards in its interview rooms, says spokeswoman Lieutenant Leslie Branch-Wise. The boards aren't intended to ferret out liars, she says, but if a suspect's drawing doesn't mesh with other details, investigators take note.