Many situations make people scream. But researchers wondered as what made a scream a scream and now, a team of researchers has found the reason. It is the ‘roughness’, an acoustic property, that makes screams different from other sounds and also adds terrifying power.

Prof. David Poeppel from New York University said that they have carried out a number of experiments to know why screams stun us. They carried screams from You Tube and 19 Volunteer screamers, who screamed in lab sound booth.

The researchers evaluated sound amplitude modulations in recordings of spoken and screamed sounds. Screamers' modulation rate was between 30 and 150 hertz, which as per the researchers was a ‘roughness’ range.

On the other hand, speakers were having slower modulations. When screams were compared with natural spoken speech and song, again more roughness level was found. When the researchers tested non-biological sounds then musical instruments were found to be having little roughness. And, alarm signals, buzzers and horns had high roughness levels.

The study researchers affirmed, “The fact that roughness appears to be used in the design of artificial alarm signals in human culture, perhaps unwittingly, underlines both the perceptual salience and the ecological relevance of rough sounds”.

The researchers also tested whether the roughness in sounds led to behavioral or neurological responses. To know the same, the researchers asked listeners to rate how scary they found noises. The noises that were found having more roughness had higher fear-inducing ratings. It is roughness that makes a scream terrifying.