Experiments on media violence were taken up in response to studies and research that established patterns of increased violence in media representations, as well as research that showed people -- including children, who may not have the same capacity as adults to differentiate between representation and reality -- are consuming far more media than they used to. In the 1990s, the popular movie "Teenage Mutant Ninja Turtles," marketed to children, portrayed 194 acts of violence. The "good guy" turtles committed 104 of those violent acts. These kinds of analyses do not substantiate the effects of violence, so controlled experiments were needed.
There are two types of experiment: laboratory and natural. Laboratory experiments are controlled studies that attempt to exclude all but one variable. Natural experiments are a form of research that compiles specific sets of data and seeks statistically probable correlations. One natural experiment that has become canonical in the study of media-and-violence is that done by Dr. Brandon Centerwell of the University of Washington. His studies showed a strong correlation between the introduction of television violence in a society and a doubling of homicide rates 10 to 15 years later. This correlation held in the United States, Canada and South Africa.
Volume 63 of the "Journal of Abnormal and Social Psychology" (1961) documented laboratory experiments with children in which two groups of children were put together to play. One group was not exposed to any media representations, and the other was exposed to representations of adults engaged in violent behavior. The experimenters concluded that the media representations significantly corresponded to increases in aggression by the children at play, and more so when media representations appeared to reward the violence. Think here about the action hero who resolves a situation by violence, then "gets the girl" at the end.
Violence in media also affects adults and adult attitudes. In the "Annual Review of Public Health," Volume 27, 2006, Huesmann and Taylor's "The Role of Media Violence in Violent Behavior" cited experiments in which men exposed to media violence were more likely to endorse violence when given hypothetical situations, as well as showing greater acceptance of antisocial behavior. Men in similar experiments were also more likely to express more adversarial sexual beliefs.