A new study out of the U.K. suggests that how much you know about public affairs has a direct effect on likelihood to vote, and that the media play an indirect -- but vital -- role in getting people to vote.
What people know "raises voter participation in clearly causal fashion." The usual socio-demographic factors matter too, like education and income. Late in the paper the author tells us "that political salience and the coverage given by mass media play a very important role in increasing voters' knowledge of political matters, in spite of their negligible direct impact on turnout."
This is researchspeak, which means basically that looking for a direct media relationship is not going to work. The media make people more informed, which in turn makes them more likely to actually participate in a democracy.
The effect is there, you just gotta know where to look for it.