When someone tells a lie it is possible to catch them out – and no, not because their pants catch on fire.
According to a study, liars are more likely to speak slowly and put less emphasis in the middle of words.
Researchers from Sorbonne University conducted a series of experiments designed to understand how we decide, based on voice alone, whether a speaker is honest.
They found that there was a signature in the voice of a liar – slower speech and less emphasis on the middle of a word – that the brain can automatically detect – even when not actively trying to determine whether someone is being honest or not.
It is hoped the discovery could be used in the future to develop ‘light tools’ that the police could use to determine whether a criminal is lying.
Study authors say if you want to be thought of as honest and confident then speak faster, put greater intensity in the middle of a word and drop pitch at the end.
These subtle changes to the way we speak are registered by the brain ‘automatically’ and it happens in a number of languages including English, French and Spanish.
The French researchers used vocal signal processing to create random pronunciations of words including rising and falling pitch.
They then asked multiple groups of volunteers whether the words were pronounced with a certainty or with honesty.
The success of human cooperation depends on mechanisms enabling individuals to detect unreliability in the people they deal with regularly.
Despite being a vital part of human society, researchers don’t really know exactly what sensory inputs humans use to determine another’s reliability.
To try and work this out, the French researchers used a data-driven method to decode the prosodic features that drive listeners perceptions of a speakers certainty and honesty across pitch duration and loudness.
‘Here we show that listeners’ perceptions of the certainty and honesty of other speakers from their speech are based on a common prosody signature,’ they said.
Prosody refers to the ‘melody’ of a phrase or word: its pitch, rate, and intensity.
‘We find that these two kinds of judgments [certainty and honesty] rely on a common prosodic signature that is perceived independently from individuals’ conceptual knowledge and native language,’ the study authors wrote.
‘Finally, we show that listeners extract this prosodic signature automatically and that this impacts the way they memorise spoken words.
‘These findings shed light on a unique auditory adaptation that enables human listeners to quickly detect and react to unreliability during linguistic interactions.’
They found that this ‘intrinsic’ ability to detect ‘signatures’ in a voice could be used to determine whether the person is telling the truth or peddling in porkies.
‘Prosody consequently conveys information on the truth-value or certainty of a proposition,’ the team wrote.
They are now trying to understand how speakers produce such prosody based on their intentions – rather than just how people perceive different pronunciations.
The findings have been published in the journal Nature Communications.