The two studies were conducted by James B. Weaver III, head of the Department of Communications Studies at Virginia Tech, and Dolf Zillmann of the University of Alabama. In one study, published in the Journal of Applied Social Psychology (1999, Vol. 29, No. 1, pp. 145-165), people were exposed to gratuitously violent or nonviolent feature films over four consecutive days. One the fifth day, approximately 24 hours after viewing to the last film, research participants took part in another project that was not ostensibly a part of the film study. Weaver and Zillmann found that, when treated either neutrally or abusively by a research assistant and then put in a position to harm this assistant, both provocation and exposure to violent films markedly increased the expression of hostile behavior toward the research assistant. The study showed that prolonged exposure to gratuitously violent films is capable of escalating hostile behavior in both men and women and of instigating such behavior in unprovoked research participants.

In a second study, published in the journal Personality and Individual Differences (1997, Vol. 22, No. 5, pp. 613-627), Weaver and Zillmann exposed research participants to four types of films -- nonviolent, old-style violence (e.g., "Glory"), gratuitous violence (e.g., "Death Warrant"), and horror (e.g., "Howling VI"). They found that men who perceived themselves as socially deviant and egocentric were more likely to accept violence as a means of conflict resolution after watching four movies with gratuitous violence. Watching old-style violence or horror movies did not have that effect. The affected men also more strongly endorsed the death penalty after watching such movies.

Note: If no author is given, the source is cited instead.