Tis the season for pumpkin spice and horror. Screams are often part of that horror, and screams and our reactions to them are rather interesting scientifically.

Scientists curious about the biology and psychology of screams had volunteers listen to screams and measured their responses. What they found was intriguing. Normally, a part of the brain called the auditory cortex processes sounds. If you hear someone speaking, your auditory cortex might help identify information like the gender of the speaker, or their tone of voice. Screams are processed somewhere else, the amygdala.

The amygdala, among other things, is one of the major centers of emotional processing of the brain. One of these emotions is fear. Upon hearing a scream, the amygdala can immediately put the body’s “fight or flight” circuits into action, preparing you to defend yourself or dash away from danger. If you hear a piercing shriek in a movie and your heart starts pounding, that’s your amygdala in action!

So what about screams makes them so scary? It isn’t their volume or high pitch, but their “roughness” that inspires terror. Roughness is a measure of how quickly a sound changes in volume. Screams that had little volume change weren’t rated as very scary while screams that had big changes in roughness were the most spine-tingling for volunteer listeners.

Though it was only recently that scientists have delved into the science of screams, it seems that we’ve had an instinctive sense of what makes a sound frightening for a long time. An artificial alarm with a lot of auditory roughness creates a similar response in volunteers as a scream would. Smoke alarms, burglar alarms, and even firetruck sirens have similar characteristic roughness as screams.

Screams, though frightening, are certainly a useful evolutionary adaptation. They not only alert us to danger, but cause our body to prepare for it. People can even judge the direction of screams better than normal sounds, allowing them to better pinpoint the source of the hazard.

Want to test your own reactions to screams? Which do you find most scary?

Kate Dzikiewicz, Paul Griswold Howes Fellow

(For more spooky science, see the Science of Horror Movies, Herbivores that Crave Meat, How Corn Created Dracula)