As promised, Katy Perry has released previews of two new songs off of Prism – and you get to decide which gets released in full on September 15.

The promotional campaign #katynow is timed with her performance at the MTV Video Music Awards this evening. She will be closing the show with the first live version of “Roar,” the first single off of her forthcoming album Prism.

Listen to the two new Katy Perry Prism songs titled “Dark Horse” and “Walking On Air” respectively.

Which Prism song do you think should be released on September 15?

Even though these are quick previews, both of them sound great and are pleasantly different from “Roar.” Head to Pepsi’s Katy Perry site to vote for which song will be released as a single, and find out tonight live on MTV which one wins.

At the time of this writing, “Dark Horse” has the lead with a large majority of the vote. We presume the runner up single will see a full release in early October.

Prism, Perry’s fourth studio album, drops on October 22.

Other performers scheduled to appear at tonight’s MTV VMAs include Lady Gaga, Miley Cyrus, Drake, Kanye West, and Justin Timberlake. Catch the event live tonight at 9 p.m. eastern/pacific on MTV.