There is, however, a correlation between the school yard variety of aggression and exposure to movie, game and TV violence, said Joel Dvoskin, a clinical psychologist and co-editor of "Using Social Science to Reduce Violent Offending."
"But correlation is not the same thing as causation," Dvoskin said. "Kids who are more violent are also more intrigued by violent imagery. It's also likely that some violent imagery can influence the manner in which people act out their aggression."
Hollywood director Cohen said that audience identification with characters can be powerful — pointing out that Colorado shooting suspect James E. Holmes was apparently influenced by Heath Ledger's portrayal of the Joker character in the previous Batman movie, "The Dark Knight."
"The creation of such an iconic character — the Joker — played by such a charismatic actor, Heath Ledger, got internalized by a disturbed young man," Cohen said.
James Steyer, chief executive of Common Sense Media, a nonprofit group that reviews entertainment media for kids, said that in the wake of the shooting, this would be a good time for the entertainment industry to take a public stance against violent images.
"Hollywood and other creators of entertainment have incredible power to shape the hearts and minds of young people," he said. "And that power comes with great responsibility to think through the images and messages contained in their creations."
Times staff writer Joe Flint contributed to this report.