Human screams have unique auditory qualities

Science : Human screams of terror are extremely effective at conveying distress and alarm, but exactly why has not been known. Now David Poeppel of New York University and his colleagues have looked beyond the measurements of sound pressure and frequency, which merely indicate that screams are louder and higher pitched than normal speech, and focused on their modulation power spectrum—how quickly a sound’s volume changes. They found that while typical speech changes less than 5 Hz, screams fluctuate rapidly between 30 Hz and 150 Hz. Those fluctuations give the sound a certain “roughness” that is unique in human vocalizations. Based on the ranking of volunteers who listened to various terror screams, the researchers found that the more screams fluctuate in volume, the scarier they are perceived to be. That’s because screams activate both the auditory cortex and the amygdala, the part of the brain attuned to emotional reactions; regular speech triggers just the auditory cortex. The natural acoustic roughness of human terror screams has been effectively mimicked in artificial systems, such as house and car alarms, which is what makes them so “super annoying and hard to miss,” says Poeppel.