Psychologists, researchers and others largely agree that subliminal messages do work, but in a limited fashion. In one study, conducted by Princeton University researchers in 2002, the word "thirsty" was added to 12 frames of an episode of "The Simpsons," and the image of a Coca-Cola can to another 12 frames. Afterward, audience members reported they were 27 percent thirstier after the show than before. Those in the control group? They said they were actually a little less thirsty [source: Locke].
In 2005, researchers at the Netherlands' Utrecht University and Radboud University were able to get subjects to select Lipton iced tea as their drink of choice after those words flashed by,although this positive result only occurred in those who were already thirsty [source: Locke]. British researchers conducted a two-week experiment where French or German music was played in the wine section of a large supermarket. On the days when French music was played, 77 percent of customers bought French wine. On German-music days, the majority purchased German wine [source: Lindstrom].
Yet despite these seemingly positive results, subliminal advertising is still seen as largely ineffective. That's because even when it's successful, it's not clear how long the results last. Maybe you'll reach for a Coke within 10 minutes of seeing a subliminal ad, but will you continue to do so the next day, week or month?
Further, some researchers caution that such messages only nudge us to do something we're predisposed to do already. They don't totally change our minds. For example, one study on subliminal messages and political candidates flashed a picture of Bill Clinton subliminally after a picture of Gray Davis, the unpopular Democratic governor of California and asked study participants to rate their favorable impression of Davis. The subliminal message only worked on independents (perhaps because they already liked Bill Clinton.) Those messages didn't seem to change the minds of Republicans [source: Locke].
So why doesn't subliminal advertising work so well? There's no consensus on the issue. A lot of the experiments with positive results were conducted in carefully controlled labs. Perhaps all of the stimuli around us in our normal lives disrupt the ability of our subconscious to notice them. Or maybe those creating the ads are flashing messages past too quickly, or producing backtracked messages that are rather garbled. Perhaps the bigger question is whether the technique will be refined in the future to produce definite, long-lasting results.