Research conducted at the University of Michigan and published by the American Psychological Association indicate that people who watched more violent television as children were more likely to shove, hit, throw things and be convicted of both criminal acts and traffic violations. A study released in 2009 by researcher Paul Boxer indicates that even when other factors such as academic and family problems are taken into account, those with a greater preference for violent entertainment as children are more likely to be aggressive in later life. Media violence alone will not turn an emotionally healthy individual into a violent one. As the Surgeon General's Report on Youth Violence concludes, ",The influence of the mass media, however strong or weak, is best viewed as one of the many potential factors that help to shape behavior."
The Centers for Disease Control and Prevention, in a discussion of violence as a public health issue that is featured on its website, has developed a model that may help clarify the role of the media in "the complex interplay between individual, relationship, community, and societal factors." that leads to violence. The CDC cites "broad societal factors that help create a climate in which violence is encouraged or inhibited. These factors include social and cultural norms." The media is a major influence in creating social and cultural norms.
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The phrase "mean world syndrome" was coined by researcher George Gerbner to summarize the effect on human consciousness of exposure to large amounts of violent television. Gerbner studied television violence throughout his 25-year career as dean of the Annenberg School for Communications at the University of Pennsylvania. In his studies, Gerbner found that people who watched more television were more likely to feel unsafe in their neighborhoods, believe that crime is an increasingly serious problem and believe that they were likely to become crime victims, whether these beliefs were supported by fact.
Violent video games, in which players are rewarded for aggression, have been blamed by some observers for extreme youth violence such as the mass shootings at Columbine High School in 1999. Psychologist Dr. Bruce Bartholow monitored the brain function of people playing violent video games and found that they became desensitized to the violence within the games. Others, such as professor Henry Jenkins of MIT, question the link between violent gaming and real-life aggression, pointing out that researchers often use artificial methods such as observing children punching a toy designed to be punched, and point out that most individuals can and do make a distinction between play and real life.