Nothing says anguish like a scream, as Edvard Munch knew World History Archive/Alamy

What is it about a piercing shriek that makes your blood run cold?

Screams have a distinct acoustic feature which grabs our attention and directly activates the brain’s fear centre. The only other sounds found so far that share this property are manufactured sirens such as intruder alarms.

A scream is one of the most primitive sounds we make. It alerts others to danger and signals that we need help, so it needs to be distinctive.


Being loud or high-pitched is not enough to stand out from the crowd of everyday sounds, says David Poeppel at New York University. His team found that screams are special because they have a property called roughness.

Acoustically, this means their volume varies at a rate between 30 and 150 hertz – faster than speech but slower than a sound with a clear pitch. To us, this just means they sound rough or raspy.

For example, compare this scream:

With this “non-rough” vocalisation:

The other sounds they analysed – musical instruments, singing and sentences spoken in three languages – did not have this property.

Before now, we assumed roughness wasn’t used in human communication, says Poeppel, but it seems to be a part of the acoustic spectrum reserved for screams, making them an unambiguous alarm.

Direct route to fear

And it’s not only nature’s alarms that make use of roughness. The team were surprised to find that the only other sounds they tested that occupied this “acoustic niche” were manufactured sirens such as car and house alarms.

For instance, compare a rough alarm:

With a non-rough flute:

It seems alarm designers have inadvertently utilised the same acoustic feature that makes screaming grab our attention. Optimising roughness could be a way to fine-tune alarms to make them even more effective.

As well as analysing screams collected from the internet and from scared volunteers, Poeppel’s team artificially manipulated the roughness of sounds and played them to other volunteers. The rougher the noise, the more scream-like it sounded and the scarier the listeners deemed it to be.

Scanning people’s brains while they listened to different noises revealed that rougher sounds, matched for pitch and loudness, increased activation of the amygdala, the fear centre of the brain, without changing the activation of the auditory cortex, where sound is processed. This suggests that rough sounds selectively activate the brain’s fear circuitry, perhaps providing a direct route for screams to affect behaviour.

The makings of a scream

There has been little formal study of human screams, says Harold Gouzoules from Emory University in Atlanta, Georgia. Poeppel’s work is “a critical contribution to the essential core question of defining screams”, he says. A better appreciation of the making and function of screams could help us better understand disorders that can involve screaming, such as dementia, as it is an especially challenging behaviour for carers to be faced with.

Sukhbinder Kumar and Timothy Griffiths at Newcastle University in the UK have found that other unpleasant sounds, such as nails on a chalkboard, also activate the amygdala. Kumar says they are interested to see if roughness could also be a feature of this teeth-clenching sound.

“Screams are interesting to study because they’re ubiquitous, universal and pretty much the first thing anyone does,” says Poeppel. Next, he plans to see if baby cries, which may be more attention-grabbing than adult screams, are even more rough.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2015.06.043