The Science of the Startle

Oftentimes, the scariest horror films are those which capitalise on the seconds before a scare, rather than the scare itself. Think The Conjuring, The Woman in Black, Insidious — all have key scenes that were made more terrifying just by the build-up towards them.

The latter of these films stands out for a particular moment. For those who have not seen James Wan’s 2010 supernatural horror, an iconic scare occurs following a psychic’s shaky account of her encounter with a demon. Throughout her dialogue, the camera flicks between her and the tormented protagonist, Josh, inching closer to their faces with every switch. The lens settles on the psychic. A bonfire-like crackle is heard. A beat. A rapid cut to Josh reveals a red-faced, crazy-eyed demon, screaming shrilly behind him. Suddenly, you are out of your seat, heart thundering, scrambling for the off button.   

This scene is a perfect example of a well-timed jump scare — an abrupt moment in horror marked by a sudden, jolting sound or visual. As it serves to startle the audience by exploiting the human nervous response, science can reveal a great deal about what makes a jump scare successful.  

There are multiple visual and auditory aspects to it, often used by filmmakers in combination. Examples belonging to the former category include close-ups of terrified expressions and camera shaking — as is seen in Jordan Peele’s Get Out and The Blair Witch Project, respectively — intended to unsettle by highlighting human vulnerability and fear. Light and dark colour contrast also helps cultivate the tense atmosphere preceding a jump scare — like in The Shining, when Billy peddles his tricycle across the blood-red and orange carpet, passing into the dingy, yellowish hallway, before encountering the twin girls dressed in powder blue.

The Shining also manages unsettling audio effectively, from the isolated, uneasy sound of Billy’s tricycle — moving from wood floor to carpet, and back again — to the high-pitched strings mirroring Shelly Duvall’s increasing horror as her character discovers Jack Nicholson’s iconic typewriter.

Although the jump scares in The Shining are fairly modest, the acoustic features present — such as frequency, volume, and sound quality — can be used to shock the brain’s fear centre. Screaming, for example, has a frequency range of 30 to 150 Hertz, which stimulates the amygdala to initiate the release of the stress hormones cortisol and adrenaline into the blood. These hormones cause elevated heart rate, pupil dilation, and sweating — all physical hallmarks of our reaction to a jump scare, termed the startle response.  

Like everything that happens in our bodies, there is an evolutionary basis to what we experience. The startle response is a component of our primal fight-or-flight instinct — how, during ancient times, quick physiological changes, like accelerated blood flow to the muscles and faster metabolism, would enable us to flee from, or face, a threat.

The immediate after-effects of this ingrained feature also explain why some enjoy the jump scare. In a 2020 study monitoring the behaviours of people participating in a haunted house experience, Danish researchers at Aarhus University found that as self-reported fear increased (up to a certain point), so too did enjoyment.

This relationship is supported by the neurobiology of thrill; immediately after a fright, once the absence of real danger has been realised, the brain releases the feel-good hormone dopamine and the mood stabiliser serotonin. These are essentially, in chemical form, the wave of relief we experience after being scared — and it is that pleasure which keeps horror fans coming back for more.

However, horror fan or not, knowing this information will not stop your muscles tightening, your heart pounding, your breath quickening, the next time you find yourself in the tense seconds before …

Image from Wikimedia Commons