I'm not sure if this is exactly what you are looking for, but two excellent scientific studies about the effects of violence are: Wilson, J. & Weiss, A. (1991). The effects of two reality explanations on children's reactions to frightening movie scenes, Communication Monographs, 58, pp. 307-325. and Hoffner, C. & Cantor, J. (1991). Factors affecting children's enjoyment of a frightening film sequence. Communication Monographs, 58, pp. 41-61. Good luck. ld