What do the greatest horror movies all have in common?

They all have memorable soundtracks that elicit an instantaneous feeling of terror. Indeed, if you view the films without any sound, they become a great deal less scary.

But what is it about the music that renders it frightening? More specifically, if sounds are simply vibrations in the air, what is it about our biology that causes us to respond with fear?

The Fear Response

With respect to evolutionary biology, there’s an evident survival advantage to the immediate recognition of a life-threatening circumstance.

Thinking takes time, particularly when you’re staring a hungry lion in the face. When every second counts, you don’t have the time to stop and process the information consciously.

Seeing that it takes additional time to process and ponder visual information, the animal brain is wired to react to faster sound-processing mechanisms—a trait that offers survival advantage and has been selected for in the wild.

And that’s precisely what we see in nature: a large number of vertebrates—humans included—generate and react to harsh, nonlinear sounds and vocalizations when frightened. This yields a nearly instant sensation of fear or anxiety.

But what is it about nonlinear sound that makes it frightening?

When an animal screams, it produces a scratchy, irregular sound that stretches the capacity of the vocal cords past their normal range.

Our brains have evolved to identify the attributes of nonlinear sound as abnormal and indicative of dangerous circumstances.

The intriguing thing is, we can artificially mimic a wide array of these nonlinear sounds to bring about the same instantaneous fear response in humans.

So, what was once a successful biological adaptation in the wild has now been co-opted by the movie industry to manufacture scarier films.

Music and Fear

We all know the shower scene from the classic movie Psycho, and it’s probably one of the most terrifying scenes in the history of film.

But if you watch the scene without sound, it loses the majority of its affect. It’s only when you incorporate back in the high-pitched screaming and bone-chilling staccato music that the fear response becomes fully engaged.

To reveal our natural aversion to this nonlinear sound, UCLA evolutionary biologist Daniel Blumstein carried out a study assessing the emotional reactions to two types of music.

Participants in the study listened to a collection of emotionally neutral scores and scores that included nonlinear properties.

As anticipated, the music with nonlinear characteristics elicited the strongest emotional responses and negative feelings. This response is simply a part of our anatomy and physiology.

Regardless of whether Hollywood understands this physiology or not, it knows instinctively that the use of nonlinear discordant sound is still the best way to get a rise out of the audience.

Want to see the fear response in action?

Check out these 10 Essential Horror Movie Scores.