SATURDAY, Oct. 31 (HealthDay News) -- Subliminal messages are most effective when they have negative words, English researchers say.

Subliminal messages are images shown so quickly that viewers don't consciously "see" them, according to background information in the University College London study.

It included 50 volunteers who were shown a series of words on a computer screen. The words appeared for only a fraction of a second, much too briefly for the participants to consciously read them. The words were either positive (for example, cheerful, peace, flower), negative (murder, despair, agony), or neutral (box, kettle, ear).

As the words were displayed, the participants were asked to choose whether they were positive, negative or neutral. Their choices were most accurate when responding to negative words.

"There has been much speculation about whether people can process emotional information unconsciously, for example pictures, faces and words. 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," study leader Professor Nilli Lavie said in a Wellcome Trust news release.

"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,'" Lavie said.

The findings, published in the journal Emotion, have implications for the use of subliminal marketing in advertising and in public service announcements, such as safety campaigns.

"Negative words may have more of a rapid impact," Lavie said. "'Kill your speed' should be more noticeable than 'Slow down.' More controversially, highlighting a competitor's negative qualities may work on a subliminal level much more effectively than shouting about your own selling points."

More information

For more on the workings of the brain, see The National Institute of Neurological Disorders and Stroke.