Hearing a person scream – whether in real life or in a movie – is a universal distress call. A team of scientists from the New York University and the Max Planck Institute in Frankfurt has conducted a study attempting to find what makes a scream so scary.

Leading author of the study published in Current Biology and an esteemed neuroscientist, David Poeppel found that all human screams have a certain modulation, and the scary part is not always given by the scream’s loudness or the fact that it’s very high-pitched.

His team started by listening to and analyzing various screams, some from horror movies and some that were recorded in a laboratory. It turned out that all screams share a common trait: roughness, which measures the fastness of how a sound’s loudness alternates.

Loudness of normal speech rarely gets out the range of 4 to 5 hertz; when it comes to screams, however, the range changes drastically, oscillating between 30 and 150 hertz. A scream’s roughness was also found to serve as an indicator of how alarming the distress call is.

Dr. Poeppel explained that screams that ranked higher in roughness led people to label them as being scarier. But researchers didn’t stop at screams, as curiosity made them want to search other sounds characterized by roughness.

Their analysis revealed that the only other signals that resemble screams in roughness are alarms, such as those that we hear on fire engines and ambulances. Even though their roughness levels weren’t criteria when these alarms were designed, it makes sense they would rank higher.

They were trying to get the people’s attention by creating a really precise and obnoxious sound, which is exactly what you need in an emergency situation.

In the study, researchers also tracked the subjects’ brain activity by MRI as they were listening to alarm signals and screams. Results showed that the amygdala – the brain region that processes and remembers fear – always lit up when screams were heard, no matter the roughness.
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