You’ve just rounded the corner of a dark and musty basement. In front of you, chained to a stone wall amid a pile of femur bones and skulls, a young girl is pleadingly mouthing the words “help me,” as a ghoulish figure paces the room.

Realizing there’s nothing you can do for her, you move on. In the next room, another figure sits beside an altar, motionless except for its pupils, which follow your approach.

Despite knowing that you’re in a fictional haunted house, you still can’t help but be scared. “We use what we know about the science of emotion to scare people,” said Lisa Feldman Barrett, a professor of psychology at Northeastern University.

The girl chained to the wall is Barrett’s daughter, Sophia. She has organized the charity event every Halloween since she was nine, raising thousands of dollars for the Greater Boston Food Bank. The ghouls are Barrett’s lab members—post docs, graduate students and research assistants, all experts in getting people to feel particular emotions.

“One thing that makes people aroused, or activated, is uncertainty,” said Barrett, who received a Pioneer Award from the NIH in 2007 for her innovative work on emotion. “Once we’ve created that high arousal, uncertain feeling: that’s when we jump.” So, as you approach the still figure beside the altar, your heart jumps into your throat when the seemingly inanimate figure thrusts out its arm.

“When someone has the expectation that something fearful might be about to happen”—knowing that you’re in a haunted house, for instance—“that potentiates the startle response,” Barrett added.

The entire show—which took place on Saturday—is meticulously choreographed: “Timing is important when you set expectancies and then violate them,” explained Barrett.

Instead of focusing on the guts and gore that characterize many haunted houses, Barrett and her team try to “build a creepy sense of terror.” But it’s also intended to be fun: “we want people to have a pleasant experience of fear instead of an unpleasant one,” she said. For that reason, they encourage visitors to explore the space. With a sense of ownership in place, the ultimate fear factor becomes even more rewarding.

Children ages two to 92 got to choose from a menu of fright levels: scary, scarier and scariest. In all cases, their fear experience was most certainly grounded in science.