How do screams scare us?

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Screams are "rough" vocalizations, like an auditory strobe light

The "rougher" the scream, the more terrifying, say researchers

CNN  — 

Whose screams raise the hairs on the back of your neck? Janet Leigh’s famous shower screech in “Psycho”? One of the many her daughter Jamie Lee Curtis belted out in the “Halloween” films? Or maybe you prefer Danielle Harris’ versions?

A new study says one thing’s for sure: The vocalizations of all these scream queens scare us because they target a special acoustic “sweet spot” in our brain, designed to snap us to attention to possible danger.

“If you ask a person on the street what’s special about screams, they’ll say that they’re loud or have a higher pitch,” said senior author David Poeppel, professor of psychology and neural science at New York University. “But there’s lots of stuff that’s loud and there’s lots of stuff that’s high-pitched, so you’d want a scream to be genuinely useful in a communicative context.”

By plotting sound waves of various screams in a similar manner to auditory neurons, the researchers discovered screams occupy a reserved chunk of the auditory spectrum not used by normal speech, which they dubbed a “privileged niche” in human communications.

“We even saw that this observation remained true when we compared screaming to singing and speaking, even across different languages,” said Luc Arnal, the study’s co-author.

What contributes to that niche, the authors said, is that screams have a unique vocal quality: roughness. But what’s “rough” about a scream? For most of us, roughness might indicate a raspy, harsh, or gravely sound or voice. However, in psychoacoustics, roughness equals dissonance, or the unpleasant qualities of a sound.

“Roughness refers to fast sound changes in loudness (in a 30-150Hz frequency range) of a sound that can be high-pitched or not,” Arnal said. If that isn’t clear, he added, then think of roughness like a strobe light.

“Everyone is familiar with those lights that flash superfast in clubs,” Arnal said. “Screams could be considered as strobophones, since they are modulating very fast in an analogous way in the auditory domain.”

Study subjects were asked to listen to different human screams as well as artificial alarms, like buzzers, car alarms and horns, and compare them to control sounds. Researchers found the screams and sounds rated “roughest” were the ones that were most terrifying to the listener.

“We found that the rougher the sound, the stronger the response in the amygdala, the part of the brain involved in fear reactions,” Arnal said. The researchers also found they could make a nonscream more terrifying and scream-like by adding roughness.

What was also “peculiar and cool” about their findings, the researchers said, is that alerting signals like car alarms and house alarms activated the same auditory range as screams.

“These findings suggest that the design of alarm signals can be further improved,” Poeppel said. “The same way a bad smell is added to natural gas to make it easily detectable, adding roughness to alarm sounds may improve and accelerate their processing.”

Wonder what the next generation of Hollywood scream queens might do with that information?

“Well yes, our results definitely show that rough screamers are the best candidates to make great horror movie actresses and actors,” Arnal said.