Subliminal messages do reach your brain - but you won't know it

People are able subconsciously to register an image even when they cannot see it, according to a study into the power of subliminal messages.

Scientists have demonstrated that hidden subliminal images can still attract the brain's attention, even when the person is apparently unaware of the visual stimulation caused by the image.

The findings may explain many everyday phenomena, such as being aware of passing advertising billboards on a busy road without actually "seeing" them, or being conscious of the messages contained in flashing adverts on a webpage.

The researchers found that the brain is able to register faint or brief images that fall on the eyes even when the person concerned insists that they have not seen the object or message.

"We've looked at whether what we pay attention to and what we are aware of, is one and the same thing because conventional psychology says they are," said Bahador Bahrami of University College London. "We found they were not. We show that there is a brain response in the primary visual cortex to subliminal images that attract our attention without us having the impression of having seen anything."

Dr Bahrami added: "The findings point to the sort of impact that subliminal advertising may have."

The experiments involved volunteers who wore glasses similar to those worn to see 3D films, where the lens covering one eye was red and the lens covering the other was blue.

A strong, flashing blue light was directed at one eye, which drowned out the faint stimulus from a series of red images that were shown to the other eye.As the volunteers were exposed to the two sets of images in each eye, they were asked to perform psychological tests of varying difficulty while the nerve activity in the brain's visual centre was scanned.

The findings, published in the journal Current Biology, revealed that the brain was still able to register the faint images, but was only able to do so when the psychological tasks it was doing were less onerous.

This means that some degree of attention is needed by the brain to register a subliminal image. If the brain is too busy doing something else, the image has no effect on it. "This is exciting research because it challenges previous thinking - that what is subconscious is also automatic, effortless and unaffected by attention," Dr Bahrami said.

Ever since the possibility of subliminal advertising was first raised 50 years ago, scientists have attempted to see whether flashing images on a television or cinema screen can be registered by the brain.

The latest study suggests that they can, but further research will be needed to assess whether such messages can have any effect on a person's purchasing decisions.

But can they change what you do?

Fifty years ago, a market researcher, James Vicary, claimed he could get American movie-goers to drink more Coca-Cola and eat more popcorn by flashing messages on the screen for a fraction of a second. He claimed cola sales jumped 57.5 per cent, but later admitted that the stunt was a fabrication.

In 1978, a TV station in Wichita, Kansas, was asked by the local police to place subliminal messages in a report on a notorious murderer, in an effort to get him to surrender. The message showed a pair of spectacles, an image thought to be relevant to him, and underneath were the words "now call the chief". The attempt failed, and the murderer was not caught until 2005.

During the US presidential race in 2000, an advertising campaign for George Bush flashed the word "bureaucrats" over pictures illustrating an election proposal by Al Gore. Another frame showed the word "rats", which led to an investigation, but no penalties were imposed.