We’ve all experienced those hellish train journeys – packed into the carriage like sardines when suddenly a screaming infant erupts like Vesuvius behind us. Why is it that human screams are so good at grabbing our attention?
One possible explanation, published this week by neuroscientists from New York University, is that human screams have a unique property that not only activates the auditory regions of the brain but also the areas associated with fear.
“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,” says David Poeppel, professor of psychology and neural science at NYU. “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.”
Using screams from YouTube videos, films and volunteer screamers, the researchers found that the volume of a scream fluctuates very rapidly in a particular range of the audible spectrum that wasn’t previously thought to be important for communication.
“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,” says Poeppel. “In a series of experiments, we saw [that] this observation remained true when we compared screaming to singing and speaking, even across different languages.”
Interestingly, alarm signals such as car and house alarms also contain the auditory region set aside for screams. What both noises have in common is a property called roughness, which refers to how quickly a sound changes in loudness. Speech tends to differ in loudness by only 1Hz, whereas screams and alarms can fluctuate rapidly (between 30 and 150Hz). When subjects were asked to judge how frightening various screams were, those with the highest roughness were rated as the most terrifying.
The researchers also monitored the brain activity of subjects listening to screams, using a technique called functional magnetic resonance imaging (fMRI). The participants were found to display increased brain activity in the amygdala, the region of the brain involved with emotion and processing fear.
So that’s something to bear in mind the next time you’re cowering behind a cushion in front of a horror film…