Back during the 2000 presidential election, George W. Bush's campaign aired an attack ad against Al Gore's health-care plan that featured a bizarre quirk. Near the end of the ad, the word "RATS" quickly flashed on the screen, barely noticeable, before the words "BUREAUCRATS DECIDE" appeared.
Gore staffers first brought it to the attention of the New York Times, which ran a story in which several experts said it looked like an attempt at subliminal messaging. Bush denied it — and the ad was pulled.
The fracas was part of a debate that's surrounded advertising for many decades: Do subliminal messages actually work? Are we at the mercy of unconscious cues being pumped into our heads by unscrupulous corporations? Or is this all just a bunch of nonsense?
Many psychologists, for their part, are skeptical of how much subliminal messages can do. "The general belief is that [subliminal messages] are pretty powerful and that they can get us to do all sorts of things that we don’t want to do. But that isn’t true," says Ian Zimmerman, who researches consumer psychology and implicit cognition at the University of Missouri–Columbia. (He wrote an interesting post recently on subliminal messages over at Psychology Today.)
However, subliminal messages do exist. And they can influence people in all different sorts of subtle ways. Researchers have been studying them for decades, and here's what we know now:
It's not true that advertisers convinced people to drink Coke by flashing messages in a movie theater
The popular concept of subliminal messages was shaped by a famous study in which researchers claimed that flashing "Drink Coca-Cola" messages in a movie theater got people to buy more soft drinks. But this study was actually a total hoax.
Back in 1957, James M. Vicary and Frances Thayer said they'd spent six weeks showing messages on movie screens so quickly that moviegoers didn't realize that they were there. The messages? "Eat popcorn" and "Drink Coca-Cola." The result? Popcorn sales went up 58 percent, and cola sales went up 18 percent. The effect was stunning.
There was just one problem. This study was a total hoax, Vicary later admitted, made up to boost his marketing company. And other researchers were never able to replicate the results. Yet that story still lives on in many minds as fact.
But subliminal messages might be able to influence your drinking habits in other ways
While the Coca-Cola movie-theater study was a hoax, it seems to have inspired a line of research about what subliminal messages can do to make people thirstier. And there have been some intriguing results here.
In 2002, researchers at Princeton University published a study in which they subliminally added 12 frames of the word "thirsty" and 12 frames of an image of a Coca-Cola can into an episode of The Simpsons.
Even though subjects couldn't guess what had been added, they rated themselves as about 27 percent thirstier after the show than before it. Those in the control group, who were only shown plain white frames, were marginally less thirsty after the show. The researchers also got similar results using images of a Coca-Cola can and a sweaty boxer.
A similar study published in 2005 by researchers at Utrecht University and Radboud University in the Netherlands demonstrated that subliminal messages could affect someone's affinity for a particular brand, in this case Lipton Ice.
Participants who were subliminally primed with the words "Lipton Ice" were more likely to choose this beverage when given a choice between two drinks. However, this effect only happened if the participants were already thirsty. In an accompanying experiment, the researchers manipulated people's thirst by having them consume a salty candy. They got similar results.
Now, remember, these are just two studies. And there are plenty of caveats for all these lab experiments, which I'll get to in just a minute.
Subliminal messages might affect our opinions of political candidates
Some researchers have also found that subtle cues in political campaign ads might actually have an impact.
Back in 2008, researchers at Adelphi University and Emory University decided to replicate Bush's "RATS" ad in a controlled study. They created campaign ads for an unknown candidate in which the word "RATS" flashed subliminally across the screen. That message increased participants' negative ratings of the candidate. Other subliminal messages, such as "STAR" and "XXXX" seemed to have no effect.
In a separate experiment in the same paper, researchers showed participants a screen in which an image of Bill Clinton flashed subliminally right before it showed an image of California Governor Gray Davis. The subliminal Clinton cue actually seemed to make independent voters like Davis a little better (or at least hate him a little less). That might be because Clinton was popular among independents. On the other hand, the subliminal cue had no effect on Republicans or Democrats — presumably because they already had strong feelings about politics.
In both experiments, researchers also made sure that the subliminal cues were actually subliminal by making people guess what subliminal message they might have seen. Only two out of 272 total participants were able to do so.
Now, these are just two studies. And it's unclear if such a subliminal message could be strong enough to affect how people vote. However, a different study published in the Proceedings of the National Academies of Sciences in 2007 did find that after being primed with a subconscious image of the Israeli flag, Israelis voted in a more politically moderate way in a real election. (Ed Yong has a good summary of that study on his blog.)
Still, this is far from a settled issue. One big question is whether the effects of subliminal messages can last long enough to follow someone from their TV all the way to the voting booth.
None of this means that subliminal messages make us into brainwashed zombies
There are many caveats to keep in mind with all these studies. For the most part, these studies are performed in very controlled environments in laboratories where there isn't much to distract from the subliminal cues. Real life, on the other hand, is full of distractions, which means that subliminal messages might get overrun by other stimuli.
Also, sometimes the effects in these studies are small, even though they're measurable. Oftentimes, subliminal messages seem to be giving people a little nudge rather than overwhelming their pre-existing inclinations. In one study, subconscious political messages only worked on political independents, and messages about Lipton Ice only worked on people who were already thirsty.
Also, it's unclear how long the effects of subliminal messages actually last. Most studies look for effects within a few minutes or hours — and haven't explored longer time points. For example, one study showed that being subliminally primed with winning-jackpot images increased people's willingness to bet, but the effect only lasted less than five minutes.
So altogether, it's unclear how much of this subliminal priming stuff would still hold up in daily life, outside of the laboratory.
As far as subliminal advertising is concerned, it's probably not worth the investment. Zimmerman says it's unlikely that advertisers are using it in the US today. "I don't think there’s any evidence to suggest that it’s more effective than just a traditional ad that we’re very aware of," he says. "Why go to the trouble?"
Still, psychologists do use subliminal priming as a tool to understand the unconscious mind
Subliminal messages can also be useful for research. Subliminal priming studies are common these days — not just to test subliminal messages themselves, but actually as a research tool in psychology.
Here's how it works. Researchers flash something subliminally and see how it affects some other task or test. For example, this study found that subconsciously priming white Americans with the word "BLACK" made them respond faster to negative stereotypes in a later word task (even among people who didn't display racist attitudes in a direct survey).
This is one example of researchers using subliminal messages to study implicit attitudes that people don't even know they have. Subliminal messages have become a tool that psychologists use to explore the unconscious mind.