A new study conducted by John Velez of Texas Tech University has concluded that cooperative play between two people in video games can decrease aggression and promote "pro-social behavior." Velez had two players on the same team playing against opponents in Halo: Reach and TimeSplitters and then gauged their behavior toward the other team and each other.

"What we found was cooperative play seems to have the biggest effect in terms of decreasing aggression toward other people," Velez said. "We found that playing with a helpful partner increases the expectation of others to reciprocate that pro-social behavior and generally be helpful. That applies to not only the teammate, but to others as well. The other interesting thing we found was when playing with a helpful teammate, you're nicer to the other team you just competed against that tried to beat you, even though you don't expect them to give it back to you."

In each game, players would either be by themselves or teamed up with another player, and at the end of each game, players were given the option to "behave aggressively toward their partner or foe by blasting them with a loud, undesirable noise." In both games, players who had a teammate were less aggressive than those who played alone.

"Generally, people playing cooperatively seemed to really focus on and value those relationships that are going on when they are playing," Velez said. "They focus more on the social aspects and focus less on the violence and aggression. It's more important to them to think about how they're interacting with other people. Since most video games are played this way nowadays, it's an important factor to think about when talking about violent video games and their negative effects."

It's an interesting idea for a study, but you really need more details on the particulars here. It'd be helpful to know what kind of people (and how many) they chose, how well they did overall and whether that affected behavior, whether that behavior changes when playing against online opponents or AI-controlled enemies, etc. To Velez's credit, he did measure whether local or online co-op made much of a difference and concluded that it didn't, which is a little surprising.

Still, I'd love to see Velez measure the aggression levels of people bouncing off each other's heads in New Super Mario Bros.: "We found that after enough deaths -- accidental or otherwise -- participants would simply refuse to release teammates from their respawn bubble."