What do the best horror movies all have in common?

They all have unforgettable soundtracks that bring about an instant sensation of terror. As a matter of fact, if you view the films without any sound, they become a great deal less frightening.

But what is it about the music that makes it terrifying? More specifically, if sounds are simply oscillations in the air, what is it about our biology that causes us to react with fear?

The Fear Response

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

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

And that’s exactly what we discover in nature: many vertebrates—humans included—produce and react to harsh, nonlinear sounds and vocalizations when alarmed. This produces a nearly instantaneous feeling of fear or anxiety.

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

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

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

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

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

Music and Fear

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

But if you view the scene without sound, it loses the majority of its impact. 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 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 scores and scores that included nonlinear properties.

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

Whether Hollywood comprehends 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 observe the fear response in action?

Check out these 10 Essential Horror Movie Scores.