Edvard Munch's 1893 painting The Scream. (Image: Munch/Public Domain)
Edvard Munch knew it, Wes Craven knew it, and no one knows it better than newborn babies—if you want to cut through the noise of the world, open your mouth and scream. There’s something about a good wail that’s penetrating enough to interrupt the deepest sleep or cut through the splashiest shark attack.
But what is it about screams that gives them that piercing immediacy?
A team of neuroscientists from the University of Geneva and New York University spent a couple of years straining their ears in order to find out. Their study, “Human Screams Occupy a Privileged Niche in the Communication Soundscapes” was published today in Current Biology. It explains what exactly makes screams different from average outbursts.
"The primal scream is the first vocal signal that newborn babies produce," says the paper's lead author. (Photo: Inferis/WikiCommons CC BY-SA 2.0)
The key turned out to be a particular acoustic property called “roughness,” which is a measure of how quickly a sound changes from soft to loud.
“There’s a lot of stuff that’s loud and a lot of stuff that’s high-pitched,” and those things don’t inspire such a visceral reaction, senior author David Poeppel told Cell Press. It takes roughness to make everyone take notice, and the researchers found that the rougher a scream was, the more fear it inspired.
The paper’s lead author, Dr. Luc Arnal, was led to this topic by a conversation with a friend of his who had just become a father—the new dad told Arnal his baby’s screams were “literally hijacking his brain,” Arnal remembers.
To better understand this sensation, Arnal started recording and analyzing screams he found on YouTube and in horror movies. When the waveforms piqued his interest, he decided he needed better-quality samples—so he turned his colleagues into a corps of “volunteer screamers” and sent them to his lab’s recording booth to do their best Fay Wrays. The team then analyzed those screams and compared them to spoken sentences, singing, and various artificial sounds. They also played the recordings to a set of extra-brave volunteers, who listened to them from within the confines of an MRI machine.
Brain activity in people exposed to "pleasant" and "unpleasant" sounds. (Figure: Arnal et. al/Current Biology 2015)
This led to another interesting finding—when people hear roughness, they have more nerve activity in the amygdala, an area of the brain associated with emotional reactions.
“Given the importance of screams in survival, it is possible that the sound information takes a fast direct route from the ear to that part of the brain,” explain Dr. Sukhbinder Kumar and Professor Timothy D. Griffiths, neuroscientists who were not involved in the study.
The instinct to scream dates back to a world where people were more often faced with immediately life-threatening situations, and is even shared with a number of animals (Arnal cites another Youtube favorite, the screaming goats). The special niche that roughness occupies in the brain means that we react to it viscerally, and the uniquely rough nature of screams means we aren’t constantly triggered by other loud things in the same alarmed way
There is one more class of particularly rough-sounding objects—fittingly, the same ones charged with protecting us from danger. Car alarms, house alarms, buzzers, and horns all displayed more roughness than your average artificial sound.
“There’s almost no paper saying that roughness should be used to make efficient alarm signals,” Arnal says, so sound designers must have figured out how to get maximum attention on their own. Here’s hoping this new knowledge doesn’t make them—or newborns—that much better at it.
Falling produces a natural scream reaction, so roller coaster denizens like these are a great source of shrieks. (Photo: SFOTPR/WikiCommons CC BY-SA 3.0)