Why do human screams have such an amazing ability to grab our attention?
A team of international scientists have found a unique acoustic property in screams that activates the brain's fear circuitry.
Luc Arnald from the University of Geneva told Radio New Zealand that what sets screams apart from other human sounds is roughness.
"Roughness is an acoustic feature that you only find in alarm signals. It basically refers to how fast the sound changes in loudness. Normal speech patterns only have slow differences in loudness."
In normal speech, volume fluctuates around four to five times per second, jumping rapidly to between 30-150Hz in screams, giving them that familiar shrill quality.
The team, at New York University, tested a variety of noises from human speech to musical instruments, and found that the only other sounds with that rough property were artificial alarms.
"It shows that acoustical engineers and sound designers have been tapping into the property of roughness just by trial and error."
Dr Arnald began using recordings from YouTube video and horror films to test the screams but eventually had to recruit 'volunteer screamers' into the lab to get more precise data.
"I asked my colleagues to come in the lab room and asked them to scream as loud as possible into the microphone, which we recorded to analyse what was different between the speech acoustic and the scream acoustic.
"The more roughness there was in the scream, the more frightening the scream was."
Culturally, screaming is unique: it is found across the world irrespective of place, culture or language, and is one of the earliest sounds that people learn to make - the report describes it as 'innate' and 'virtually universal.'
Read the full report, published in Current Biology, here.