Screams occupy a privileged acoustic niche to ensure their biological and social efficiency.
An international team of neuroscientists from the Max Planck Institute for Empirical Aesthetics, New York University and the University of Geneva has proved the uniqueness of screams for the first time. In a study, they discovered that screams possess very special acoustic properties: This makes them a specific type of vocal expression which is only used in stressful and dangerous situations.
“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.”
In several studies, which have now been published in the journal Current Biology and carried out by Poeppel together with Adeen Flinker, his colleague from New York, and Luc Arnal, Andreas Kleinschmidt and Anne-Lise Giruad from the University of Geneva, the researchers discovered a special acoustic trait only exhibited by screams. “Screams have a trait called ‘roughness’. Roughness occurs when screams obtain a temporal structure due to change of amplitude or frequency. If these changes happen very quickly, the ear is no longer able to ‘break down’ these temporal changes – such sounds are then perceived as rough and unpleasant. Normal speech has a modulation rate of around 4 to 5 Hz, but for roughness the rate is between 30 and 150 Hz – the temporal changes are therefore significantly faster.”
In one study, the researchers created a bank of sounds containing many different types of human vocalizations (screams and sentences) and artificial sounds (the sound of an alarm). Here they found that both the 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.
These results were supported by 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 (e.g. screams and alarms) and indicate which seemed “alarming.” Their results showed that subjects rated the screams and alarm sounds as more disturbing the higher the rating on the roughness scale.
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 ensures their biological and ultimately social efficiency – we use them only when we need them,” observed Poeppel.
Source: Max Planck Institute
Image Credit: The image is in the public domain
Original Research: Abstract for “Human Screams Occupy a Privileged Niche in the Communication Soundscape” by Luc H. Arnal, Adeen Flinker, Andreas Kleinschmidt, Anne-Lise Giraud, and David Poeppel in Current Biology. Published online July 16 2015 doi:10.1016/j.cub.2015.06.043
Human Screams Occupy a Privileged Niche in the Communication Soundscape
•We provide the first evidence of a special acoustic regime (“roughness”) for screams
•Roughness is used in both natural and artificial alarm signals
•Roughness confers a behavioral advantage to react rapidly and efficiently
•Acoustic roughness selectively activates amygdala, involved in danger processing
Screaming is arguably one of the most relevant communication signals for survival in humans. Despite their practical relevance and their theoretical significance as innate [ 1 ] and virtually universal [ 2, 3 ] vocalizations, what makes screams a unique signal and how they are processed is not known. Here, we use acoustic analyses, psychophysical experiments, and neuroimaging to isolate those features that confer to screams their alarming nature, and we track their processing in the human brain. Using the modulation power spectrum (MPS [ 4, 5 ]), a recently developed, neurally informed characterization of sounds, we demonstrate that human screams cluster within restricted portion of the acoustic space (between ∼30 and 150 Hz modulation rates) that corresponds to a well-known perceptual attribute, roughness. In contrast to the received view that roughness is irrelevant for communication [ 6 ], our data reveal that the acoustic space occupied by the rough vocal regime is segregated from other signals, including speech, a pre-requisite to avoid false alarms in normal vocal communication. We show that roughness is present in natural alarm signals as well as in artificial alarms and that the presence of roughness in sounds boosts their detection in various tasks. Using fMRI, we show that acoustic roughness engages subcortical structures critical to rapidly appraise danger. Altogether, these data demonstrate that screams occupy a privileged acoustic niche that, being separated from other communication signals, ensures their biological and ultimately social efficiency.
“Human Screams Occupy a Privileged Niche in the Communication Soundscape” by Luc H. Arnal, Adeen Flinker, Andreas Kleinschmidt, Anne-Lise Giraud, and David Poeppel in Current Biology. Published online July 16 2015 doi:10.1016/j.cub.2015.06.043