What is it that makes screams so bloodcurdling and attention-grabbing? A new study finds that humans seem to be built to respond to scream-like noises, whether they come from a baby, a person in danger, or even an alarm or siren.
"We found that screams occupy a reserved chunk of the auditory spectrum," said New York University's David Poeppel, senior author of the study, in a news release. "In a series of experiments, we saw [that] this observation remained true when we compared screaming to singing and speaking, even across different languages."
It makes sense: in a world where there are all manner of loud and shrill noises, a unique and immediately identifiable signal of distress is a useful thing to have. The secret seems to be in what the scientists call the scream's "roughness," which is how quickly it changes in loudness.
Normal human voices naturally "modulate" between slightly louder and softer tones, though you don't really notice. Screams, however, modulate very quickly, giving a harsh edge to the sound as its loudness bounces up and down a hundred times a second or more. This pattern cuts right through other noise and is recognized by our brain, attracting our attention and activating our fear center — because if someone else is scared, you might want to think about getting scared, too.
The paper, led by the University of Geneva's Luc Arnal and published Thursday in the journal Current Biology, describes this as a "privileged acoustic niche."
Understanding how screams make everyone listen to them may make for improvements to things like alarms and sirens — coincidentally, the only sounds tested that also seemed to activate the fear response in humans, though possibly for a different reason. By bumping up the "roughness" in these noises, we may be able to make them more audible in loud environments like concerts, or from longer distances.
The researchers hope now to study baby screams specifically, to see if, as one might expect, those sounds feature a particularly distinctive roughness. After that, they hope to learn whether other animals share this "acoustic niche" and whether it's inherited from species to species.