It’s a sound that makes us sit bolt upright and look around with alarm: the sound of a human scream. But why do we react in such a way? A new study attempts to get the bottom of that.

Apparently, it’s because screams use a sonic quality that is referred to as “roughness,” and that activates a neural response that is related to fear, according to a Christian Science Monitor report. The study was published in the journal Current Biology.

The researchers behind the study, David Poeppel and Luc Arnal, both neuroscientists, determined that screams were in a sort of “acoustic niche” in the human brain that isn’t shared by any other human vocalizations.

It doesn’t seem terribly surprising that screams would alarm us, as one human indicating danger should cause other humans to take notice on an evolutionary basis. But scientists wanted to really dig in deep and understand the biology behind it, and they found that although screams seem like a simple loud and high-pitched noise, what was surprising was the nuances behind it.

The researchers conducted what they termed an “unconventional” acoustic study, in that they had a group listen to a bunch of different human and non-human sounds, rating them based on the alarmingness of it.

They found that it’s not the volume or pitch that is important in a scream, but its “roughness.” When the frequency modulates more quickly than our ears differentiate, this is known as “rough” and it sounds unpleasant to us. This roughness correlates closely with feelings of fear in the brain.

Screams and artificial alarm sounds fall within this domain of “roughness,” the study found.