What do the best horror movies all have in common?

They all have unforgettable soundtracks that arouse an instantaneous feeling of fear. In truth, if you view the films without any sound, they become a lot less scary.

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

The Fear Response

With respect to evolutionary biology, there’s an obvious survival advantage to the immediate acknowledgment of a harmful 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 consciously.

Considering it takes longer to process and contemplate visual information, the animal brain is wired to react to quicker sound-processing mechanisms—a characteristic that provides survival advantage and has been selected for in the wild.

And that’s exactly what we see in nature: numerous vertebrates—humans included—produce and respond to harsh, nonlinear sounds and vocalizations when frightened. This produces a nearly instant feeling of fear or anxiety.

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

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

Our brains have evolved to distinguish the properties of nonlinear sound as unpleasant and indicative of dangerous situations.

The intriguing thing is, we can artificially replicate a variety of these nonlinear sounds to get the same instantaneous 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 are familiar with the shower scene from the classic film Psycho, and it’s probably one of the most frightening scenes in the history of cinema.

But if you view the scene on mute, it loses most of its impact. It’s only once you add 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 evaluating the emotional reactions to two types of music.

Study participants listened to a collection of emotionally neutral scores and scores that incorporated nonlinear elements.

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

Whether Hollywood comprehends this physiology or not, it appreciates intuitively that the use of nonlinear disharmonious sound is still the most effective 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.