People are more confident about their choices if the message is negative
People can perceive subliminal messages, particularly if the message is negative, according to a UK study.
In three experiments at University College London, participants were briefly shown masked words and asked to classify them as emotional or neutral.
The study, published in the journal Emotion, says being able to react to tiny cues helps us to avoid danger and may have useful marketing uses.
But critics say there is no evidence this would work outside a laboratory.
A SUBLIMINAL HISTORY
1957 market researcher James Vicary claimed that flashing messages on a movie screen in New Jersey had made people purchase more food and drink
He coined the term "subliminal advertising"
In 1958 the UK, America and Australia banned the practice
In 1962 James Vicary admits he falsified the results
In 1974 despite no evidence that it worked the UN said it was a major threat to human rights
In 1985 Dr Joe Stuessy told the US Senate that more research was needed on the subliminal messages in heavy metal music
In 1990 the band Judas Priest was taken to court by parents of boys who killed themselves after listening to their music. Judas Priest said if they wanted to use subliminal messages they would be to tell the kids to buy more records
Professor Nilli Lavie from University College London showed 50 participants a series of words on a computer screen.
Each word appeared on-screen for only a fraction of a second - much too fast for the participants to consciously read the word.
The words were either positive (eg cheerful, flower, peace), negative (eg agony, despair, murder) or neutral (eg box, ear, kettle).
After each word, the participants had to choose whether the word was neutral or emotional (positive or negative) and how confident they were of their decision.
The researchers found that the participants answered most accurately when responding to negative words, even when they believed they were merely guessing the answer.
They were able to accurately categorise 66% of the negative words compared to 50% of the positive ones.
Professor Lavie said: "We have shown that people can perceive the emotional value of subliminal messages and have demonstrated conclusively that people are much more attuned to negative words.
"Clearly, there are evolutionary advantages to responding rapidly to emotional information.
"We can't wait for our consciousness to kick in if we see someone running towards us with a knife or if we drive under rainy or foggy weather conditions and see a sign warning 'danger'.
Subliminal advertising is not permitted on television in the UK.
But Professor Lavie said her work could be applicable to marketing campaigns: "Negative words may have more of a rapid impact - "Kill Your Speed" should work better than "Slow Down".
"More controversially, a competitor's negative qualities may work on a subconscious level much more effectively than shouting about your own selling points."
The study was funded by the Wellcome Trust.
But marketing psychologist, Paul Buckley, of the Cardiff School of Management, said there was no evidence that subliminal messages work in the real world: "From a practical point of view this probably doesn't reflect what would happen in real life.
"Certainly lots of countries around the world have legislation to ban subliminal messages being used on television and nobody has yet been able to point to any instance where a subliminal message has worked."