What do the greatest horror movies all have in common?

They all have unforgettable soundtracks that arouse an immediate sense of fear. As a matter of fact, if you watch the films without any sound, they become a lot less frightening.

But what is it regarding the music that renders it terrifying? More specifically, if sounds are just oscillations in the air, what is it about our biology that causes us to respond with fear?

The Fear Response

In regard to evolutionary biology, there’s an obvious survival advantage to the immediate recognition of a threatening scenario.

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

Considering that it takes longer to process and ponder visual information, the animal brain is wired to respond to swifter sound-processing mechanisms—a trait that offers survival advantage and has been selected for in the wild.

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

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

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

Our brains have evolved to detect the characteristics of nonlinear sound as unpleasant and indicative of hazardous situations.

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

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

Music and Fear

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

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

To demonstrate our instinctive aversion to this nonlinear sound, UCLA evolutionary biologist Daniel Blumstein carried out a study examining the emotional responses to two types of music.

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

As predicted, the music with nonlinear characteristics elicited the most powerful emotional responses and negative feelings. This response is simply an integral part of our anatomy and physiology.

Whether Hollywood understands this physiology or not, it knows intuitively that the use of nonlinear disharmonious sound is still the best way to get a rise out of the audience.

Want to witness the fear response in action?

Listen to these 10 Essential Horror Movie Scores.