The birth of subliminal advertising as we know it dates to 1957 when a market researcher named James Vicary inserted the words "Eat Popcorn" and "Drink Coca-Cola" into a movie.
The words appeared for a single frame, allegedly long enough for the subconscious to pick up, but too short for the viewer to be aware of it. The subliminal ads supposedly created an 18.1% increase in Coke sales and a 57.8% increase in popcorn sales.
Vicary's results turned out to be a hoax. But more recent experiments have shown that subliminal messages actually can affect behavior in small ways.
A Harvard study from 1999 employed a similar method to Vicary's -- subjects played a computer game in which a series of words flashed before them for a few thousandths of a second. One set got positive words like "wise," "astute," and "accomplished." The other set got words like "senile," "dependent," and "diseased."
Despite the fact that these words flashed far too quickly to be consciously perceived, those who received positive words exited the room significantly faster than those who got negative words.