In the 1959 film "The Tingler," obsessed scientist Vincent Price battled a centipedelike creature that only human screams could kill. Beyond felling a B-movie monster, screaming has remarkable power, piercing through other sounds to provoke an urgent sense of danger. And a new study is turning an ear toward what exactly makes screams so terrifying.
"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 study senior author David Poeppel, who heads a speech and language-processing lab 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."
And that was the jumping-off point for the scientists. [15 Weird Things Humans Do Every Day, and Why]
Bring on the scream queens
To find out that special something about screams, Poeppel and his colleagues needed to listen to a lot of screaming. With little research on the subject to draw from, they turned to movies and YouTube videos to harvest a crop of sample screams. They also recruited volunteer screamers to howl wordless shrieks and scream entire sentences ("Oh my god help me!") into a sound-booth microphone. The scientists were looking for a quality in screams and screamed phrases that sets them apart from other loud or high-pitched noises.
A new method of sound analysis called the modulation power spectrum (MPS) proved to be the key. It displays the rate at which sound intensity changes, identifying an acoustic range occupied by screams, but not by ordinary speech. According to the MPS, screams exhibited a quality called roughness, which means their volume rises dramatically and quickly, study lead author Luc Arnal, a neuroscientist at the University of Geneva, told Live Science in an email. This change in volume is measured in cycles per second, or Hertz (Hz.) Normal speech has a roughness that ranges between 4 and 5 Hz — meaning the volume doesn't change much in any instance. But screams can modulate much faster, ranging from 30 to 150 Hz, the team found.
"We found that screams occupy a reserved chunk of the auditory spectrum, but we wanted to go through a whole bunch of sounds to verify that this area is unique to screams," said Poeppel, who also directs the department of neuroscience at the Frankfurt Max-Planck-Institute. "In a series of experiments, we saw [that] this observation remained true when we compared screaming to singing and speaking, even across different languages. The only exception — and what was peculiar and cool — is that alarm signals (car alarms, house alarms, etc.) also activate the range set aside for screams," Poeppel said in a statement.
And the higher the roughness, the scarier the sound, said people asked to judge the screams. The researchers also monitored brain activity in study subjects as they listened to screams and other sounds. Screams triggered increased activity in the amygdala, the region of the brain that processes fear response. Interestingly, when scientists manipulated non-threatening sounds to increase their roughness, the listeners' fear responses increased, as well, with more activity in the amygdala.
I scream, you scream
Many animal species use specific vocalizations to communicate immediate threats, so perhaps it's not surprising that human brains are hardwired to recognize and respond to screams as a uniquely human alarm call, Poeppel said. Further studies will investigate infant screams, which typically evoke a strong response in listeners, to determine if these sounds demonstrate exceptional roughness.
"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 vocalization."
The finding is detailed today (July 16) in the journal Cell Press.