What makes a truly good scream so bad to listen to

Many sounds can be loud, obnoxious, or irritating in some way or another. Repeated whining from kids in the back seat of the car about arriving at the beach comes to mind. But even the most grating yelling, singing, etc. doesn’t have that special je ne sais quoi of a true scream. Either from an adult or a child, a real scream grabs our attention in a way different from all other human vocalizations. We can’t ignore it. And now thanks to Professor David Poeppel, we can understand why.

The special sauce of a true scream comes from how much the amplitude or volume level modulates per second. Casual speech may vary in volume four or five times per second, but a scream is jumping up and down a 100 times per second. That doesn’t leave much time to perceive each shift in volume in order to cram in that many changes in a single second, but the overall effect is described as a “rougher” sound. Rough sounds generally feel abrasive and unpleasant, and in a scream they reach activate a specific part of our brain as you hear it.

What your brain thinks of a scream

Test subjects in an fMRI listened to a variety of sounds to see what part of their brains reacted to what qualities. Screams, as defined above, were unique in triggering activity in the amygdala, where our fear responses originate. Since babies are inherently excellent screamers, it’s thought that they helped shape the evolution of this extreme response to these sounds. A baby and parent reacting quickly to danger or other needs probably increased the odds of the infant’s survival.

This possibly primal origin doesn’t mean that qualities of a scream have not been co-opted by other parts of our society though. Many people have similar reactions to alarms, including many alarm clocks. These mundane devices may be jarring and unpleasant, but thanks to the amygdala, are hard to ignore.

Source: Screaming For Science: The Secrets Of Crying Babies And Car Alarms by Jon Hamilton, Shots