320 college students played either a violent or a nonviolent video game for approximately 20 minutes. A few minutes later, they overheard a staged fight that ended with the "victim" sustaining a sprained ankle and groaning in pain. People who had played a violent game took significantly longer to help the victim than those who played a nonviolent game---73 seconds compared to 16 seconds. People who had played a violent game were also less likely to notice and report the fight. And if they did report it, they judged it to be less serious than did those who had played a nonviolent game.

In the second study, the participants were 162 adult moviegoers. The researchers staged a minor emergency outside the theater... The researchers timed how long it took moviegoers to [help]... Participants who had just watched a violent movie took over 26 percent longer to help than either people going into the theater or people who had just watched a nonviolent movie.

These studies clearly show that violent media exposure can reduce helping behavior. People exposed to media violence are less helpful to others in need because they are 'comfortably numb' to the pain and suffering of others, to borrow the title of a Pink Floyd song.