No smoking signs may be driving more people to light up, a psychological study suggests. Scientists say the messages have an 'ironic effect on smokers that increases their craving for tobacco. Without being aware of it, they react to the signs by thinking of and wanting cigarettes. 'You get ironic effects when you couple information that people perceive with negation, said researcher Brian Earp, from Oxford University. 'When I say dont think of a pink elephant, Ive just put the thought of a pink elephant in your head. A lot of public health messages are framed in a negative way - say no to drugs, dont drink and drive, no smoking. 'No smoking signs in particular are everywhere. If youre a smoker walking down a street youre likely to pass five or six of these signs in windows or on doors. If you have a chronically positive attitude to smoking this could boost your craving. To test the theory, Mr Earps team first primed a group of smoking volunteers from a town in New England, U.S., by showing them a number of photographs. Some included a no smoking sign in the background or at the edge of the picture, while others had the signs edited out. Next, the same volunteers took part in a 'joystick test looking at their reactions to a series of screen images. The technique is widely used to assess instinctive tendencies to embrace or avoid certain stimuli. Moving the joystick away is associated with avoidance, while drawing it towards the body indicates a desire to bring the stimulus closer. In a series of experiments, the researchers showed that participants who had earlier been shown no smoking signs were more drawn to smoking-related images such as ashtrays and cigarettes.MO