Screaming works

Particularly harsh modulations cause the alarm effect of screaming

Screams are alarming and hard to ignore - but what makes them acoustically so unique? © FreeImages.com / ralaenin
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Whoever cries, stands out: the loud call of a man can still be heard even in the case of great noise. Why this is so, researchers have now found out. Accordingly, screams differ from other sounds due to their special acoustic properties. Their unique "roughness" ensures their alarming effect in stressful and dangerous situations. In the journal "Current Biology", the researchers also describe how screams act on the anxiety center in the brain.

We've all heard screams and even shouted, "Everyone has a rough idea of ​​what makes screams, " says David Poeppel of the Max Planck Institute for Empirical Aesthetics in Frankfurt. However, to describe what makes a loud exclamation only the unmistakable cry, is already more difficult. Above all, they are loud, high and shrill. "But that alone is not enough, " says Poeppel. "Like other sounds, they can be high and loud, but they also have unique modulation that other sounds do not have."

Everyone screams

Screaming, however, is an important means of communication: "It is one of the earliest sounds anyone produces - across all cultures and ages, " Poeppel explains. The crying of an infant is virtually impossible to ignore. In addition, many species of animals also scream. However, what sets us apart is the ability to distinguish screams from understandable speech patterns. Poeppel and his colleagues wanted to find out what makes the screams so unique and why we react so specifically to them.

The neuroscientists initially created a database of different sounds. This included human sounds such as spoken sentences and screams, but also artificial sounds such as the ringing of an alarm clock. In addition, they added simple sound intervals to the collection, including "pure" and "dirty", that is, dissonant tone combinations. In addition, the researchers collected screams from movies and YouTube videos and also had some volunteers record different screams and phrases.

Roughness makes screams uncomfortable

A comparison of the acoustic properties of all these sounds showed that the cries are characterized by a characteristic called "roughness". Roughness occurs when the volume or frequency of a sound changes sharply and rapidly. "When these changes happen very quickly, hearing is no longer able to 'resolve' these temporal changes, " Poeppel explains. "One perceives such a sound then as rough and thus as unpleasant." Display

Modulations in a certain frequency range provide for the particularly penetrating "roughness" of the cries. Arn Luc Arnal

In normal human speech, this modulation frequency is four to five hertz, so it is not particularly rough. Screams and dissonant intervals, such as a dirty fifth, on the other hand fall in the range of 30 to 150 hertz: they change in time so much faster and are thus rough and penetrating.

Alarm clocks are modeled on screams

Interestingly, alarm signals such as the ringing of an alarm clock or an alarm on the car have such roughness. The manufacturers of such devices have evidently modeled on the modulation of human screams through trial and development the alarm is thus more penetrating and effective.

How effectively these harsh sounds actually affect people, the scientists examined in a follow-up experiment. Subjects listened to the recordings from the database and were asked to rate how scary or "alarming" they sound. It was confirmed: screams and screaming phrases seem all the more frightening, the higher they are on the "roughness scale".

Anxiety Region responds to cries

In the end, the researchers looked for the area in the brain that processes such sounds. Using functional magnetic resonance imaging, they recorded the subjects' brain activity while they heard the screams. Both cries and alarms triggered an increased activity in the amygdala. This brain region is responsible, among other things, for processing and remembering anxiety.

"Screaming really works, " says Poeppel. "Overall, our results show that screams prove a preferred acoustic niche. This ensures their biological and, ultimately, their social impact - we only scream if we have to. "Researchers also want to continue to focus on human cries, especially exploring the pervasive babble of babies and toddlers. They also want to investigate how human and animal cries differ, and how this trait is conserved between different species. (Current Biology, 2015; doi: 10.1016 / j.cub.2015.06.043)

(Max Planck Society / New York University / Cell Press, 17.07.2015 - AKR)