You may not realize it, but watching movies manipulates your brain. Not only does your brain become synchronized with the other brains around you, but specific effects can focus that attention on specific details on the screen.

This might seem creepy, but it's all due to the magic of an entertaining movie.

Uri Hasson, a Princeton University psychologist, discovered that when movie-goers were watching classic Western film "The Good, The Bad, and The Ugly." During that film, their brain activity increased and decreased at the same time as others also watching the movie. This synchronization included those parts of the brain that recognize sound, as well as those parts that process and recognize images.

But what causes this synchronization? Hasson determined to find out. He found that movies that use structured devices with shots that are carefully composed are most likely to control viewers' brains. He used a group of volunteers watching "Dog Day Afternoon," and took brain scans: 70 percent of the brains of those viewers were "synched" up.

"The movie takes over the brain responses of the viewers," says Hasson.

However, after watching content from improvised and reality TV shows, which are less structured, viewers had considerably less brain synchronicity: less than five percent.

Filmmakers believe this makes sense. Brains being in synch during a movie suggests that the people who are watching it are enjoying it. Less brain synchronicity may mean that their minds are wandering because the film hasn't captured their attention.

Tim Smith, a vision scientist from the University of London, did a similar study, but tracked eye movement from 75 people as they watched an action clip from "Iron Man 2." Researchers translated the eye tracking data to a heat map and then placed the map over screenshots of the film. Most of the eye movement gravitated to key things happening on-screen, including the two superheroes fighting.

The scene used CGI for most of its effects.

"We're constantly calculating where we think the audience's eye is going to be, and how to attract it to that area and prioritize within a shot what you can fake," says Jon Favreau, director of the film. "The best visual effects tool is the brains of the audience. They will stitch things together so they make sense."

What's most interesting about this research is that filmmakers seem to understand how visual perception works inherently, and perhaps that's a talent that often goes unrecognized.