(Newser) – What makes a scream a scream? A rough sound is not how people typically describe a scream, though. But there’s lots of stuff that’s loud or high-pitched.
The researchers then asked volunteers to rate how frightening the different screams were, and found that the more “roughness” there was in a scream, the more the volunteers were scared by it. Beyond felling a B-movie monster, screaming has remarkable power, piercing through other sounds to provoke an urgent sense of danger.
Loudness of normal speech rarely gets out the range of 4 to 5 hertz; when it comes to screams, however, the range changes drastically, oscillating between 30 and 150 hertz. The researchers also downloaded various sound clips from the Internet. The group asked volunteers to listen to a variety of the terror screams and sentences, some modulated to be more or less rough than usual. Why, though, are we able to so quickly distinguish the meaning of a human scream? Roughness is essentially the audio equivalent of super-fast strobe lights, which can intensely stimulate the visual part of the brain and feel similarly unpleasant.
They share these characteristics with non-human sounds such as shrieking auto or house alarms. “That’s why you want to throw your alarm clock on the floor”, Poeppel says. In addition, notoriously dissonant pairs of notes such as the so-called “devil’s interval” also contained screamlike rough frequencies.
Finally, in order to see how these sounds are processed, the researchers monitored the brain activity-using functional magnetic resonance imaging (fMRI)-of the study’s subjects while they listened to these sounds. For both screams and the alarm sounds, the brain showed increased activity in the amygdala, which is the region of the brain used for processing and remembering fear.
Researchers also found that numerous kinds of artificial alarm signals feature high levels of roughness, even though there has been very little scientific study done on roughness and its effects, suggesting that alarms succeed in alarming people more by accident than design.
Next, the team tried to assess whether that roughness in sounds was associated with behavioral or neurological responses.
Poeppel adds that his group would like to study not only other species, but other types of screams-such as screams of passion or rallying cries at sporting events-as well as the tell-tale screams of human infants to find out whether they have the same properties and activate the brain in the same way.
“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”.
According to recent research, the answer to the first question lies in the acoustic properties of the scream itself. Where in the brain we process this information is known, but there was one area that scientists assumed didn’t have much to do with human communication.
Duplicating that quality, outlined in the latest issue of the journal Current Biology, could lead to everything from scarier films to new and improved alarm sounds.
But exactly why we scream has remained a mystery.