Researchers had subjects view different images with each eye; the image paired with negative gossip tended to stay longer in subjects' consciousness. Ed Yong editorializes:
Our brain offers up a view of reality that allows us to get on with our lives, but that’s always somewhat of an illusion. It might be disheartening to learn that we focus on the bad rather than the good, but it is also easy to imagine why this is. As [researchers Eric Anderson and Erika Siegel] write, “this preferential selection for perceiving bad people might protect us from liars and cheaters by allowing to us to view them for longer and explicitly gather more information about their behaviour.”
The Dish 