RENEE MONTAGNE, host:
This is MORNING EDITION, from NPR News. I'm Renee Montagne.
When the Supreme Court last week overturned a California ban on selling violent video games to kids, the justices were in wide agreement that these games don't really harm young people.
There's no such agreement among scientists. When NPR science correspondent Shankar Vedantam looked into scientific studies about the effect of violent games, he found those studies reaching opposite conclusions.
(Soundbite of video game)
Unidentified Man: You probably thought you weren't going to die today.
SHANKAR VEDANTAM: There is strong disagreement among researchers about how much games like "Grand Theft Auto" and "Postal" affect young people. The irony is that scientists who think the games are harmful, and those who think they're not, are both looking at the same evidence. They just see two different things.
Most experiments into the effects of violent video games are done with college students. Researchers divide them into two groups. One plays a violent game; the other, a non-violent game. Then researchers measure how students in each group feel and how they behave.
Now, you can't give young people guns and knives to see whether they'll kill each other after playing a violent video game, so scientists have come up with other ways to measure emotional responses.
Social psychologist Brad Bushman decided to show students violent pictures: one of a man shoving a gun down another man's throat, a second of a man holding a knife to a woman's throat.
Dr. BRAD BUSHMAN (Social Psychologist): What we found is for people who were exposed to a lot of violent video games, their brains did not respond to the violent images. They were numb, if you will.
VEDANTAM: Bushman also had the students blast each other with loud noises.
Dr. BUSHMAN: We try to make the noise as unpleasant as possible, by thinking of every noise you hate. So like, fingernails scratching on a chalkboard, dentist drills, sirens.
VEDANTAM: We're going to keep the volume down, but in the experiment, this is the kind of sound students inflicted on one another.
(Soundbite of screeching sound)
VEDANTAM: And they could make it as loud as a smoke alarm, if they wanted. Some students got really mean.
Dr. BUSHMAN: Everybody was more aggressive if they'd played a violent game than if they'd played a non-violent game. And the more numb they were, the more aggressive they were in terms of blasting their opponent with loud noise through headphones.
VEDANTAM: That sounds airtight. Bushman believes that violent video games desensitize young people. Compared to people in the real world who are gentle and compassionate, students playing these games are mean and hurtful.
And then there's Chris Ferguson, a psychologist at the Texas A&M International University. He's conducted similar experiments, and also sees the same behavior changes among students. But he interprets them entirely differently.
Ferguson says compared to people in the real world who shoot and stab one another, the changes in behavior he's seen among students are transient and trivial.
Dr. CHRIS FERGUSON (Psychologist, Texas A&M International University): Most of the debate now is really onto these kind of minor acts of aggressiveness, which is just thinking negative things about another person. You know, maybe, you know, we're talking about little children essentially sticking their tongues out at each other, or that sort of thing.
VEDANTAM: Ferguson says it's easy to think senseless video game violence can lead to senseless violence in the real world. But that's mixing up two separate things.
Dr. FERGUSON: Many of the games do have morally objectionable material, and I think that is where a lot of the debate on this issue went off the rails. We kind of mistook our moral concerns about some of these video games, which are very valid - I find many of the games to be morally objectionable - and then assume that what is morally objectionable is harmful.
VEDANTAM: In other words, define harm as getting in trouble with the police, and violent video games aren't a risk. But if you're worried about lesser kinds of harm, they can be a risk.
Here's Brad Bushman again.
Dr. BUSHMAN: Playing violent video games probably will not turn your child into a psychopathic killer, but I would want to know how the child treats his or her parents, how they treat their siblings, how much compassion they have.
VEDANTAM: And so on. So it turns out that the dueling scientific studies really aren't really at odds with each other. They just make different assumptions, which may be why Bushman and Ferguson agree on one thing: As fathers, they've banned their own kids from playing violent video games.
Shankar Vedantam, NPR News.