You can start by checking out research on subliminal messaging. To summarize, subliminal messaging works to some degree, but it is much less effective than superliminal communication. For example, will showing a dark gray coke bottle silhouette, so dark that you don't even know you're seeing it, in the momentary blank screen between movie previews cause people to decide to go buy a soda? It will probably influence a couple people, but not as many as would be influenced by just replacing the blank screen with a big, bright, picture of a coke, with the Coca-cola logo and condensation dripping down the glass. That said, there is evidence that you can "prime" someone with subliminal information. Priming, though, is more about getting people to recognize something more quickly later than it is about getting them to change their behavior.