You may also want to see if individual difference in cognitions, behaviors, etc. Are related to transportation theory. Even with exposure people with lower scores on movie modified transportation scale may nor become as psychologically impacted. That scale can be found online and wold have to be modified (with permission) for movies versus literature.

Some of the research projects that I have looked at exposed children to two types of movies (e.g., violence-oriented movies and no-violence content movies) to understand the impact. Definitely, the social learning theory, particularly, modeling provides a framework for understanding the psychological impact of movies on children. You could conduct an experiment as suggested by Leow. You do indeed need to define specific psychological factors that you wish to assess.