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Human screams have a unique acoustic property that triggers the brain’s fear centre more effectively than almost any other sound, scientists have found.
After testing a variety of noises, including human speech and musical instruments, the only other sounds that appeared to activate the brain in a similar way were car alarms and police sirens, the study found - perhaps explaining why they are so unpleasant to listen to and almost impossible to ignore.
David Poeppel, a professor of neuroscience at New York University who led the work, said: “We found that screams occupy a reserved chunk of the auditory spectrum.”
The study found that screams are distinguished by an acoustic quality known as “roughness”- the rate at which the volume of a sound changes.
In normal spoken conversation, volume fluctuates around four to five times per second (4-5Hz).
The roughness of screaming is much higher, at between 30-150Hz.
The rising and falling volume is so rapid that it is not perceived as such, but is ultimately what makes screams sound so shrill and unpleasant.
Having pinpointed the acoustic quality that elicits our emotional response to screaming, it would be theoretically possible to design even more gripping alarms or to tailor the audio from horror film screams to make them more frightening, according to Poeppel.
“You could optimise alarm sounds to make them scarier,” he said.
“You could even tailor your alarm to your individual needs so you could decide how blood-curdling would you like your wake-up call to sound.”
The researchers began by isolating the acoustic qualities of screams that distinguish them from other sounds, showing that almost no other sound had similar levels of “roughness”.
“The only exception, and what was peculiar and cool, is that car alarms and house alarms also activate the range set aside for screams,” said Poeppel.
The scientists also carried out fMRI brain scans of people while they were played a variety of noises, including a repository of scream sounds taken from YouTube recordings and volunteer screamers, who recorded themselves in a laboratory sound booth.
The study, published in Current Biology, found that while all sounds activated the auditory cortex, screams also triggered activation in the brain’s emotional centre, the amygdala, which is involved in fear processing.
They also found that the rougher a scream, the stronger the activation in this region and the volunteers also described rougher screams as more distressing to listen to.
“Screaming really works,” Poeppel said.
“It is one of the earliest sounds that everyone makes. It’s found across cultures and ages, so we thought maybe this is a way to gain some interesting insights as to what brains have in common with respect to vocalisation.”


Fear factor: Why human screams set alarm bells ringing inside your brain

The Scream, by Edvard Munch. The unique properties of human screams have a powerful effect on the brain. Photo: AP

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