Scientist sees similarity in screams, sirens as alert signals

Screams are unmistakable, universally recognizable as distress calls. A new study has found that all human screams are modulated in a particular way.

“We asked ourselves what makes a scream a scream,” said David Poeppel, a neuroscientist at New York University and the Max Planck Institute in Frankfurt, Germany, and an author of the report “Human Screams Occupy a Privileged Niche in the Communication Soundscape,” published Aug. 3 in Current Biology.

He and his colleagues analyzed screams in movies and those recorded in a laboratory. The scientists found that all screams share a trait called roughness, which is a measure of how fast the loudness of a sound changes.

In normal speech, loudness ranges between 4 and 5 hertz; for screams, the range is 30 to 150 hertz. The researchers also found that the roughness of a scream serves as a measure of how alarming the call is.

“The more roughness they have, the more scary people ranked the screams,” Poeppel said.

Inspired by these findings, the researchers looked for other sounds with roughness. The only other signals resembling screams in this way were alarms like those on ambulances and fire engines.

“This wasn’t known when they were designed, but it makes good sense,” Poeppel said. “These are sounds that are really precise, obnoxious and attention- getting, and that’s what you want.”

The researchers also monitored brain activity in study subjects using functional magnetic resonance imaging as they listened to screams and alarm signals.

Screams triggered increased activity in the amygdala, a region of the brain used for processing and remembering fear, the scientists found. The more roughness a scream had, the more activity it generated in the amygdala.