A team of New York University neuroscientists has identified the "acoustic signature" of screams, a study that points to the unique attributes of this form of expression and suggests we are able to generate sounds reserved exclusively for signaling distress.
"Everybody screams and everybody has an intuition about what constitutes screams--that they are loud and high-pitched," says David Poeppel, the paper's senior author and a professor in NYU's Department of Psychology and Center for Neural Science. "But neither turns out to be quite correct. In fact, screams have their own acoustic niche separate from other sounds. While, like some sounds, they may be high-pitched and loud, screams are modulated in a particular way that sets them apart from the rest."
The other co-authors of the paper, which appears in the journal Current Biology, include: Luc Arnal, a former NYU post-doctoral fellow and now a researcher at the University of Geneva; Adeen Flinker, an NYU postdoctoral researcher; Andreas Kleinschmidt, a professor of neurology at the University of Geneva; and Anne-Lise Giraud, director of the University of Geneva's Auditory Language Group.
In their study, the researchers identified the nature of a particular acoustic characteristic that is specific to screams.
"Screams have trait called 'roughness,' which refers to how fast a sound changes in loudness," explains Poeppel, also director of the Max Planck Institute for Empirical Aesthetics in Frankfurt.
He adds that a standard measure of sound amplitude modulation--how loudness changes in speech--is Hertz (Hz), or cycles per second. Normal speech rates are typically between four and five Hz, but for roughness, the rate is between 30 and 150 Hz--a remarkably higher rate.
To reach its conclusions, the research team conducted both experiments and analyses that measured sound modulation and identified which parts of the brain were active while listening to screams and other sounds.
In one experiment, they created a bank of sounds, downloaded from the Internet, containing several types of human vocalizations (screams and sentences), artificial sounds (alarm [e.g., a buzzer] and instrument sounds) and sound intervals (pure tone intervals such as "a perfect fifth"). Here, they found that the recorded screams and the artificial alarm sounds and dissonant intervals, such as a "mistuned fifth," fell into the roughness domain (30-150 Hz)--a finding that suggests alarm manufacturers have effectively captured the modulation of a human scream--while the other sounds did not.
The scientists supplemented these results with laboratory experiments in which one group of subjects, which included men and women, recorded a series of sounds: screams, screamed sentences ("It's right behind you!"), meaningless vocalizations ("aahhhhhh"), and normally spoken sentences. As with the earlier findings, both screams and screamed sentences occupied the "roughness domain" while the other sounds did not.
In an effort to further confirm the findings, the researchers had another group of subjects listen to these sounds, which included both screams and alarms as well as other sounds, and indicate which seemed "alarming." Their results showed that subjects rated the screams and alarm sounds as more disturbing than the others depending on roughness: the rougher the sound rating, the scarier it seems.
Finally, in order to see how these sounds are processed, the researchers monitored the brain activity--using functional magnetic resonance imaging (fMRI)--of the study's subjects while they listened to these sounds. For both the screams and the alarm sounds, the subjects showed increased activity in the amygdala, which is the region of the brain used for processing and remembering fear.
"As a whole, our findings show that screams occupy a privileged acoustic niche that, because they are separated from other communication signals, ensures their biological and ultimately social efficiency--we use them only when we need them," observes Poeppel.
The research was supported, in part, by a grant from the National Institutes of Health (2R01DC05660).