Say it like you mean it (Image: Lucasfilm /20th Century Fox/The Kobal Collection)

Watch what you say, or rather, how you say it. People judge how confident you are in just 0.2 seconds.

Xiaoming Jiang and Marc Pell of McGill University in Montreal, Canada, made this discovery by attaching 64 electrodes to the heads of volunteers and taking electroencephalograms (EEGs) while they listened to recorded statements.

The statements – phrases like “they don’t drink alcohol” – were spoken by actors or public speakers aiming to sound confident, nearly confident, unconfident or neutral. A different group of volunteers confirmed the confidence level of the recorded statements before the test subjects listened to them.


Jiang and Pell saw event-related potentials – positive peaks in brain activity – in all the volunteers’ EEGs around 200 milliseconds after the start of a clip, no matter its confidence level. However, more confident speech had higher peaks than unconfident speech. A higher peak within such event-related potentials has previously been associated with increased processing of information. Nearly-confident voices seem to be given additional consideration with an extra pattern of brain activity occurring at about 330 milliseconds.

Exuding confidence

“We found that when a speaker is very confident about something, this can be assessed at a very early stage,” says Jiang. Confident voices eliciting higher brain activity suggests that listeners’ brains might have a preference for confident statements, assigning them more attention and processing them more quickly, he says.

“People are rapidly waking up to the realisation that we obtain strong representations of perceived personality from a speaker’s voice,” says Phil McAleer, at the University of Glasgow, UK. Last year, he showed that people make judgements of a speaker’s dominance, trustworthiness and attractiveness in under a second.

So what makes us sound confident, or not? It’s hard to say – Jiang and Pell’s analyses revealed that confident voices were pretty similar acoustically to nearly-confident voices, but somehow prompted a different pattern of activity in listener’s brains. Unconfident statements, on the other hand, tended to be higher in pitch and slower than all other expressions, as well as rising in pitch towards the end. Neutral statements were acoustically closer to confident ones, although they were lower in pitch, higher in intensity and spoken more rapidly.

The fact that impressions about a speaker are made so quickly reflects the importance of assessing another person’s mental state. “Any information about the mindset of others is relevant to us,” says Annett Schirmer at the National University of Singapore. Assessing confidence is particularly useful because it allows you to estimate how accurate a speaker believes their information to be, she says.

Sensitive females

When subsequently asked to score the recordings for confidence, female participants gave more extreme scores for confident and unconfident voices than did their male counterparts. This may mean females have a stronger ability to judge vocal confidence, suggests Jiang.

The EEG readings supported this theory. When played neutral-sounding statements, females showed additional sustained increases in brain activity around 1000 milliseconds after the start of the speech – a pattern that has previously been shown to occur when making judgements incorporating extra information. It suggests women may use additional, pragmatic knowledge to inform their decision on a speaker’s confidence, says Jiang.

“There is substantial evidence already that women are better at detecting nonverbal cues that are subtle or that are presented outside the focus of attention,” says Schirmer. Sex chromosomes and hormones appear to have a role in this, but the full reason is uncertain.

McAleer describes the study as fascinating, saying that it reminds him of an oft-quoted Jedi mind trick from Star Wars, when Obi Wan Kenobi saves his robot friends simply by telling the stormtroopers firmly “these aren’t the droids you’re looking for”. “I wonder if it would have had the same effect had his voice wavered in the middle – probably not.”

Journal reference: Cortex, DOI: 10.1016/j.cortex.2015.02.002