To be persuadable, people need to sense unity between what they see, the sounds they hear and the words they understand. If my body language says “I am very nervous” and my voice says “I am extremely embarrassed”, then the exciting possibilities of my big idea are unlikely to enjoy a great reception. It doesn’t ring true. So people watching and listening conclude it probably isn’t true.
Psychological studies have given persuaders a morally troubling get-out clause to this need for congruence. Multiple experiments have suggested that people are very bad at detecting deception. We can weed out liars from truth-tellers only 55% of the time – even supposed experts like police officers. That’s a bad hit rate. It seems, when they try, people can marshal their bodies and voices to lend credence to untruths.
But – William von Hippel and Robert Trivers cast doubt on that in a new paper, The evolution and psychology of self-deception. They suggest that laboratory studies of deception suffer from design flaws that reduce detection rates.
By contrast, diary research shows people’s lies are uncovered around 20% of the time, with a further 20% falling into the ‘possibly uncovered’ category. Even these figures, von Hippel and Trivers suggest, may be under-estimates.
If, in real-life scenarios, you have a significant chance of being rumbled as a liar, with all the reputational destruction that entails, it should be a tremendous incentive to tell the truth. Decency is restored. Thank goodness. But here’s the troubling part. If you look and sound like you have something to hide – even though you are telling the truth – then people might draw an unkind inference from the way you put ideas across. Perhaps you look nervous because you hate public speaking. Perhaps your voice is monotone because that’s just the way you always talk. But it might not seem that way to your perceptive audience.
In a world where people are good at detecting lies, is not only important to tell the truth, but to avoid giving signals that mimic those given off by liars. Body language and voice must match your message. What people see and hear must fit the words you speak.