Research Finds A New Trick To Telling If Someone Is Lying: Their Voice

The recent pandemic of misinformation has made us recognize just how important it is to know if someone is telling us the truth. Some lies in 2021 are easy to recognize, like space lasers starting wildfires in California or lizard people controlling the world. But other lies are less obvious.

Now researchers have identified a built in mechanism our brain uses to detect when someone is telling us a lie: their voice. Not only did the researchers find that our voices betray a particular sound signature when we tell the truth, but that our brains also pick this up in other people automatically.

It’s all about prosody. Prosody refers to the qualities of our voice: how rhythmic it is, and were we stress tones. You might think of prosody as the musicality of a voice. If that’s still confusing, than think of an adult speaking playfully to a child. Their voice goes up and down with a sing-song quality. On the other hand, if a voice lacks prosody we would call it flat and expressionless.

So in order to see how people tell lies, the researchers studied the prosody of how they said things. And they studied people who spoke different languages, which led them to conclude that people tell lies the same way in English, French or Spanish.

The researchers grouped what people said into two categories: certain/honest or uncertain/dishonest. Then they recorded participants making statements and tracked how people perceived them. A speaker was thought to be uncertain or dishonest began with less intensity at the beginning of the word, said the word with a rising intonation, and spoke more slowly with a more variable pitch. In other words, they sound like my son when he tells me that he has brushed his teeth. People sound like they are trying harder when they are lying.

On the other hand, people sounded more certain or honest when they spoke with a faster speech rate, placing greater intensity in the middle of the word. Listeners found it especially convincing when the speaker’s pitch fell at the end of the word. People speak faster when they are telling the truth because telling the truth takes less effort.

Here’s what someone sounds like when they are being honest:

And not only did people use these different prosodic signatures when they had an audience, they also sounded this way depending on how certain they felt when they were alone. The fact that these patterns happened in three different languages led the researchers to think that “prosodic signature carries ‘natural’ rather than culturally learned, language dependent ‘conventional’ meaning.”

If the researchers are right, and there’s a natural encoded way of telling the truth or lying in humans that crosses culture, this could be incredibly helpful for evaluating what people tell us. However the study used three western languages, which does not eliminate the possibility that this is a western way of lying, and not common to all cultures in the world.

But the most interesting finding was that the different prosodic signatures or honesty or dishonesty immediately impacted the working memories of the listeners. The listeners brains automatically registered a perception of whether the speaker was truthful or not, even when the listener wasn’t being asked to determine honesty.

It’s exciting to think that we have a built in way to detect if someone sounds reliable or unreliable. But this leaves us with two problems. First, we need to hear the voice to detect the lie. Not hearing someone’s voice in tweet is probably a big reason why social media is so effective at spreading misinformation.

Second, since certainty and honesty sound the same, the prosodic signature does nothing to help us detect the most powerful liars of all. Because the best liars believe their own lies, they will sound certain when they share their claims.

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