What's especially interesting for me is, naturally, the connection to reward value. Hearing an unknown reference can make tracking it down reinforcing--sometimes so much so that I head for my computer and do it right away. Talk about creating motivation. It's almost like a mystery to be solved.
What makes it sufficiently reinforcing that this happens? Lots of factors, of course. If the reference is made by someone I chat with regularly. If it's positive and comes up more than once or twice. If it's relevant to what I do, or something else I find rewarding. Even if I hear total strangers discussing it, if it sounds sufficiently humorous or important or popular. You can generate your own list, an interesting exercise in understanding your own motivations. If I'm crunched for time--recall that we always have choices between different consequences--then I might forget it, or make a note of it for the weekend.
Sometimes the effects are considerably delayed. I'm not sure what finally did it, but after resisting for years, I finally read the whole Harry Potter series and saw the movies. Now I know what everyone was talking about!