A Very PharPoint Halloween: The Science Behind Screams

Day Two of #SpookyScience: Why do we find screams so scary?

Welcome to Day Two of PharPoint’s #SpookyScience article series! Every day until Halloween, we’re going to be posting all about things that go bump in the night – and why we have certain experiences with fright. Yesterday, we explored the science behind goosebumps, which you can read here.

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Shrieks, Screams, and Shrills: A Reflex for a Reason

When something terrifying happens – when someone sneaks up on you, or you find a spider in your bed, or the killer bursts through the door in that horror flick – you scream. It’s reflexive and intuitive, and oftentimes, we realize there’s no real threat to our safety halfway through the screech. But while most screams are overreactions to brief moments of surprise, there’s actually a reason why we shriek – and why we find them so frightening.

We often take the act of screaming for granted, because it’s such a natural reaction to fear. What is less intuitive, however, is why we find the sound of screams scary. It’s why they’re abundant in horror movies (and sometimes overused – ever heard of the Wilhelm scream?), and why haunted houses include them in their soundtracks. A good shriek sets the mood for mischief and hijinks. But why?

 

First, let’s start by looking at why our natural reaction to fear is to scream. The answer is similar to the science behind goosebumps – it’s an evolutionary advantage that has prolonged our survival since our early ancestors. Screams have been used to alert fellow animals of nearby danger, because they’re an easy way to grab attention over distance. This is still the case throughout the animal kingdom; a notable example is the prairie dog, which will often yell an alarm call to nearby members of the community when a predator is present. This is probably why babies are still born screaming – it’s been a way to alert the parent that there’s now another life to look out for.

Not All Screams Are Created Equal

While this may seem fairly intuitive, it still doesn’t explain why shrieks send a chill up our spine, or why they’re most effective for communicating danger. It turns out that until recently, science hadn’t found an explanation either – until NYU psychology professor David Poeppel and his colleagues performed an experiment to figure out what makes screams so spooky.

To do this, Poepple began collecting screams from movies and from YouTube videos. Then, volunteers came into the lab and provided some bloodcurdling yells themselves. A database of screams was built, and then each yell was ranked on a scale according to how frightening study participants found them.

scream-graphic-1One of the key takeaways is this: not all screams are created equal. There are several factors that differentiate screams from normal speech, and from each other. First, while normal speech varies in loudness between 4 and 5 Hertz, a scream can range anywhere from 30 to 150 Hertz, a much wider range.

Another key characteristic is something that Poeppel defines as “roughness”. This defines the rate that the sound modulates in its volume, and isn’t something that plays a role in how we decipher regular speech (as the volume normally stays more constant). In other words, the quicker a scream elevates in loudness, the more terrifying we find it.

To pinpoint the physiological reason behind our fearful reaction to the stimulus, Poeppel’s team observed the brains of 16 participants via MRI as they listened to the recorded screams. Their results made a lot of sense – screams activate the brain’s amygdala, which is the region where we process fear (most other sounds are processed by the brain’s auditory context). And the “rougher” the scream, the more the amygdala is stimulated.

Screams Are On the “Danger Station” – and We’re Always Tuned In

This information shows that the brain is “uniquely tuned” to pay attention to screams, like a radio station. It’s why we’re far more likely to accurately detect the direction a scream came from, but may struggle to determine direction of normal speech. It’s also why we can detect the differences in a baby’s cries – the “hungry cry” versus the “sleepy cry” versus the “sick cry”. Now that we are beginning to examine screams scientifically, we may be able to learn more about how the earliest humans communicated – and will definitely continue to learn how we communicate today.

So the next time you hear a scream that makes your blood run cold, look around for any possible danger – and then tell your amygdala to calm down!

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