This article contains spoilers from popular horror movies and shows.

Imagine you’re in the movie theater watching 2018’s “Hereditary.” During one of the film’s most unsettling sequences, the main character, Peter, wakes up in bed disoriented. As he sits up, you hear a couple of gasps from others in the audience. The camera stays locked on Peter as he moves through his house and enters the dim living room.

You hear it again: more gasps. The lighting is low, a droning score builds tension, and your heart rate climbs. The people around you continue to audibly react. You haven’t seen anything scary yet, so what is everyone else responding to?

The camera slowly pulls back, and then you see her: Annie, Peter’s possessed mother, crouched on the ceiling in an unnatural way.

Watch the scene again and you might notice that Annie was in the shadows on the ceiling the whole time, following Peter through the house.

How could you have missed a human being on the ceiling, in plain view?

As a cognitive psychologist who studies visual perception, I’ve noticed that horror movies often exploit the gap between what’s in front of your eyes and what you consciously see. Directors and cinematographers act like folk cognitive psychologists, intuitively drawing your attention exactly where it needs to be to create a scare.

Directing your attention

Horror movie fans have pointed out numerous examples of spooky figures and other unnoticed details in the background of scenes.

These blind spots exist because your visual system can’t process everything in a scene at once. You extract detailed information only from wherever........

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