One of the best ways to catch someone in a lie is to distract them while they are not telling the whole truth, according to a new study.

The extra cognitive effort required to construct a lie and do something else at the same time is what makes the lie not stand up well.

For example, the secondary task needs to be seen as important by the lying person or they will be able to prioritize the lie over whatever else they are supposed to be doing.

According to the researchers behind the new study, interviews could be structured in a certain way to involve secondary tasks. Further work is required to fully understand how multitasking affects liars.

Our research shows that truths and lies can sound plausible if lie tellers are given enough time to think about what they are saying.

When the opportunity to think becomes less, truths often sound more plausible than lies.

When the interviewees were told that the secondary task was important, the lies sounded less plausible.

The experiment worked like this: Volunteers were given their opinions on societal topics in the news, and then split into two groups for mock interviews. They were told to either lie or tell the truth.

The groups were further divided into three. One-third were given a second task to do and told it was important in order to pass the interview, one-third also had a second task but no information about how important it was, and the final third didn't have any second task to worry about.

The participant was asked to write down a seven-digit car registration number that had been shown to them. The interviewer ranked what they had heard from the study participant in several different areas at the end of the interview.

The researchers wrote in their paper that the most diagnostic differences between truth tellers and lie tellers were plausibility, immediacy, directness, and clarity.

The results were in line with what the researchers were expecting. Making up details, trying to not get caught out by those fictitious details, and keeping the falsehoods sounding as true as possible are all part of telling lies. A lot of brainpower is required.

For the best results in rooting out liars, the team suggests that the secondary task needs to be seen as important or something that has to be done.

Some people are better at lying than others, so there will always be other variables to consider. This is an interesting way of trying to show up lies when they are being told one that doesn't require any special setup and which you could try out yourself.

The pattern of results suggests that the introduction of secondary tasks in an interview could facilitate lie detection, but such tasks need to be introduced carefully.

The research was published in a journal.