(Cognitive Psychology: A Student's Handbook, Michael W. Eysenck and Mark T. Keane)
In 1957, it was reported in the press that James Vicary flashed the words EAT POPCORN and DRINK COCA-COLA for 1/300th of a second numerous times during the cinema showing of a film. This subliminal advertising allegedly led to an 18% increase in the cinema sales of Coca-Cola and 58% increase in popcorn sales. However, the film (Picnic) contained scenes of eating and drinking, and the increased sales were probably due to the film itself rather than the subliminal advertising. This conclusion is based on the fact that there is very little evidence from over 200 studies that subliminal advertising is effective in changing behaviour (Pratkanis & Aronson, 1992).
Pratkanis, A. R., & Aronson, E. (1992). Age of propaganda: The everyday use and abuse of persuasion. New York: W.H. Freeman.