FLICKR, HANS VAN DEN BERG“It isn’t that it is always loud, high-pitched or shrill,” David Poeppel, a neuroscientist at New York University and the Max Planck Institute in Frankfurt, told The New York Times (NYT). But a scream is unmistakable—it nearly always engenders are particular reaction, motivated by fear. Somehow, screams signal danger.
To figure out why, Poeppel and his colleagues analyzed the acoustic signatures of various sounds and found that screams are very “rough,” meaning that they typically involved large changes in loudness. Functional MRI scanning revealed that this quality of screams led to more activity in brain’s emotional center, the amygdala, while most sounds trigger activity only in the auditory cortex. The researchers published their results last week (July 16) in Current Biology.
The sirens of ambulances and fire engines are also rough, the researchers found, and participants reported screams that have been altered to be less rough to be less scary. “The more roughness they have, the more scary people ranked the screams,” Poeppel told NYT. The roughness of unmanipulated screams ranged from 30 to 150 hertz. Normal speech, on the other hand, was around 4 or 5 hertz.
“There’s been so much attention paid to understanding speech and song that we’ve really ignored this much more innate vocalization until now,” Tecumseh Fitch, an evolutionary biologist and cognitive scientist at the University of Austria who was not involved in the work, told Science. “They’ve made a nice start to understanding this and I think it could be a great way going forward to learn more about the neural basis of emotion.”