What do the top horror movies all have in common?

They all have unforgettable soundtracks that arouse an instant sense of terror. In truth, if you watch the films without any sound, they become a lot less scary.

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

The Fear Response

In terms of evolutionary biology, there’s an evident survival advantage to the instantaneous detection of a detrimental scenario.

Thinking takes time, especially 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 deliberately.

Seeing as it takes longer to process and think about visual information, the animal brain is wired to respond to swifter sound-processing mechanisms—a characteristic that provides survival advantage and has been selected for in the wild.

And that’s exactly what we discover in nature: several vertebrates—humans included—emit and respond to harsh, nonlinear sounds and vocalizations when alarmed. This generates a virtually instantaneous 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 normal range.

Our brains have evolved to identify the qualities of nonlinear sound as unpleasant and indicative of life-threatening circumstances.

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

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

Music and Fear

We all are familiar with the shower scene from the classic film Psycho, and it’s definitely one of the most terrifying scenes in the history of cinema.

But if you watch the scene on mute, it loses most of its affect. It’s only when you add back in the high-pitched screeching and bone-chilling staccato music that the fear response becomes thoroughly engaged.

To demonstrate our natural aversion to this nonlinear sound, UCLA evolutionary biologist Daniel Blumstein conducted a study evaluating the emotional responses to two types of music.

Study participants listened to a selection of emotionally neutral music scores and scores that included nonlinear elements.

As predicted, the music with nonlinear characteristics elicited the most potent emotional reactions and negative feelings. This response is simply a natural part of our anatomy and physiology.

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

Want to observe the fear response in action?

Listen to these 10 Essential Horror Movie Scores.