From Spiegel, Daniel Kahneman explaining how “priming” prompts behavior:

“SPIEGEL: Professor Kahneman, you’ve spent your entire professional life studying the snares in which human thought can become entrapped. For example, in your book, you describe how easy it is to increase a person’s willingness to contribute money to the coffee fund.

Kahneman: You just have to make sure that the right picture is hanging above the cash box. If a pair of eyes is looking back at them from the wall, people will contribute twice as much as they do when the picture shows flowers. People who feel observed behave more morally.

SPIEGEL: And this also works if we don’t even pay attention to the photo on the wall?

Kahneman: All the more if you don’t notice it. The phenomenon is called “priming”: We aren’t aware that we have perceived a certain stimulus, but it can be proved that we still respond to it.

SPIEGEL: People in advertising will like that.

Kahneman: Of course, that’s where priming is in widespread use. An attractive woman in an ad automatically directs your attention to the name of the product. When you encounter it in the shop later on, it will already seem familiar to you.” (Thanks Browser.)