Positive Messages Produce Better Voter Turnout?

During an election season so rife with widespread negativity, I recently came across an interesting piece on politics and behavioral science on The Blog at Huffington Post titled "Accentuate the Positive: Behavioral Science and Politics." The piece argues that as opposedto telling potential voters that turnout is expected to be low as a means for encouraging them to get out and vote, positive messages such as turnout is expected to be high or even "thanking people for voting in earlier elections," is what ensures a larger turnout. Given this, the post also goes on to ask, "if voters turn out to vote when provided with positive messaging, why is it that negative campaigning works?" This is a good question and I'm wondering what you think the answer is? I'm also wondering whether this election season is any kind of exception and I'm also hoping you will share your thoughts in the Comments section below. Thanks.

(Photo - http://www.housingworks.org/advocate/detail/take-a-stand-on-what-moves-you-vote-today-and-in-november/)