The science of screams deciphered

Ever wondered why human screams can pierce through even a noisy environment and alert people? The answer lies in the unique acoustic property of a scream that triggers the brain’s fear circuitry into action.  The same principle is used in burglar alarms that catch our attention no matter the din around.

 A study, published on Thursday in the journal  Current Biology , by Luc H. Arnal, from the University of Geneva, Switzerland, found that screams occupy a unique auditory spectrum — 30-150 Hz. This space is well distinguished from normal speech (4 and 5 Hz) across languages, thereby making it particularly difficult to ignore or confuse with other communication signals.

The team found that the 30-150 Hz spectrum is reserved for communicating danger by activating the fear response in the human amygdala and not the auditory cortex.

 The researchers found that it was a property called roughness (which refers to how fast a sound changes in loudness) that helped communicate the danger signal of a scream by specifically targeting the neural circuits involved in processing fear/danger.

 Interestingly, when volunteers screamed with different frequencies, the rougher screams were perceived as more alarming, possibly by targeting the sub-cortical neural circuits, and also enabled faster appraisal of danger.

Spatial location

The speed and accuracy in identifying the precise location of screams by the volunteers was far greater compared with regular vocalisation.

When roughness was added to non-screams, the human response was the same as to that of screams.

This fact could be used to increase the roughness of alarms to make them even more discernible and produce immediate response with better spatial location, scientists said.

Published in The Hindu on July 17, 2015