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Screaming is exhibited by many animals, but no species uses this extreme vocalization in as many different contexts as humans. Though we're pretty good at recognizing a scream when we hear one, the wide variety of screams makes it difficult to pin down what defines them. To study screams is to probe the fuzzy boundary that separates humans from the rest of the animal kingdom. It is a way to explore our pre-linguistic past. Although we are fully symbolic creatures today, on occasion a trace of our primal selves bubbles to the surface in the form of a scream. Understanding its characteristics could improve the treatment of nonverbal patients, help fight crime, or simply make movies more frightening. But first scientists need to explain what makes a scream a scream. 

To that end, researchers at Emory University’s Bioacoustics Laboratory recruited 181 volunteers to listen to short recordings of 75 nonverbal human vocalizations, such as screams, laughter, and crying. For each of the 75 sounds, the volunteers were asked to indicate whether they thought it was a scream. The researchers then analyzed 28 acoustic signatures of the sounds, such as pitch, frequency, and timbre, to determine which parameters influence the perception of a sound as a scream. 

Most people would say that the defining characteristic of a scream is that it is a focused loud and high-pitched, but previous scream research suggests otherwise. In 2015, David Poeppel, a neuroscientist at New York University and the Max Planck Institute, led a study to determine the acoustic qualities that differentiate fearful screams from other nonverbal vocalizations. To do this, Poeppel and his colleagues compiled a corpus of screams lifted from YouTube videos and ones recorded in their lab, then asked volunteers to rank them according to how alarming the sound was. Poeppel also imaged the brains of his volunteers as they listened to screams to see how these sounds affected neural activity.