In Greek mythology, the Sirens were dangerous sea-nymphs living in cliffy and rocky islands. With their enchanting songs, these half-bird half-woman creatures lured ships to wreck on rocky shores and then killed the sailors. Even today, sirens lead to nothing but destruction. The wailing sound of air-raid sirens in Ukraine reminds us of the essential reality of Siren songs ‘warning for danger’. Even in peace, we hear public warning sirens if nothing but for testing, just like the ones echoing across the streets of the Netherlands on the first Monday of every month. But why are siren sounds so efficient to signal danger and what really happens in the brain when we hear an alarming sound?

Alarming sounds, whether coming from horror movies or natural sources, chill us to the bone. Screams, car horns, ambulance sirens, just to name a few. Why do they trigger emotions of urgency, anxiety or fear, and immediately catch our attention? Obviously, they are loud and high-pitched sounds. However, not every loud or high-pitched sound sends shivers down our spines as screams do for instance. Remember how you feel when you hear your favorite singer or the harmony of musical instruments at a concert. Quite a pleasant feeling, right! So what makes the alarming sounds unpleasantly unique and why can we not ignore them? 

The answer lies in an acoustic space that was previously thought to be irrelevant for communication. Neuroscientist Luc Arnal and his colleagues indicate that, unlike speech, screams have a sound quality called ‘roughness’. Roughness can be described as the rapid repetitive acoustic modulations of a sound. In everyday speech, this modulation is typically between 4 and 5 times per second. Screams, on the other hand, fluctuate at least 6 times more quickly than speech. These fast fluctuations create an unpleasant sensation. Imagine auditory roughness as a strobe light, flickering very fast, or maybe as an aversive buzzing sound.

With increasing roughness, sounds become more annoying and worrying. Take a baby’s cry for instance! It is so stressful that we immediately get into an alert state, being a parent or not. Interestingly, artificial alarm signals also contain a high degree of roughness. Car horns, alarm clocks, or civil defense sirens are among some examples. This acoustic niche clearly has a survival benefit: to warn us about danger. How about well-known measures of sound such as loudness or pitch? Can they not have the same function? Yes, but the problem is that they are not unique to alarming sounds. Pitch and loudness, which express danger, can also distinguish word meanings as in Dutch, e.g. VOORnaam ‘first name’ vs voorNAAM ‘respectable’. So pitch and loudness are not only crucial for paralanguage (‘non-verbal communication’)  but also for language (‘verbal communication’).

In our recent research, we investigated how the brain processes language and paralanguage in parallel. We asked ourselves whether the brain can distinguish, let’s say, VOORnaam from voorNAAM and differentiate an angry voice, as being of alarming nature, at the same time. And the answer was yes! Most importantly, the brain could extract emotional information even after the effect of loudness and pitch are minimized. This supports that the brain goes beyond conventional measures to segregate alarming sounds from other communicative sounds. Roughness, in that sense, provides a good example. Being unique to alarming sounds, it prevents false alarms in normal communication so that we do not end up panicking in vain. Normally, when we hear a sound, our brain tries to make sense of it. Roughness, on the other hand, hijacks the brain and puts us in survival mode. How come? Rough sounds are directly delivered to the amygdala: a brain region that is linked with fear and danger processing. When alarmed by these sounds, the brain activates a fight-or-flight response and speeds up our reaction to survive the threat. No wonder rough sounds are chosen to signal danger, naturally and artificially.

In Homer’s epic poem, Odysseus managed to pass the island of Sirens in safety, while still enjoying their enchanting songs, by binding himself to the ship and sealing his men’s ears with wax. How are we going to survive the sirens today? Nature equipped us with an excellent survival mechanism: an instinct to fight or flight when alarmed. But it also endowed us with the ability to thrive and make judicious choices. Our political decisions have the power to make a change. We are not fated to live with WARnings but instead can silence the sirens for good.

This blog post was written by Hatice Zora

Further reading

The Odyssey of Homer.

Arnal, L., Kleinschmidt, A., Spinelli, L., Giraud, A-L., & Mégevand, P. (2019). The rough sound of salience enhances aversion through neural synchronisation. Nature Communications, 10, 3671.

Arnal, L., Flinker, A., Kleinschmidt, A., Giraud, A-l., & Poeppel, D. (2015). Human Screams Occupy a Privileged Niche in the Communication Soundscape. Current Biology, 25, 2051–2056. 

Zora, H., & Csépe, V. (2021). Perception of prosodic modulations of linguistic and paralinguistic origin: Evidence from early auditory event-related potentials. Frontiers in Neuroscience, Auditory Cognitive Neuroscience, 15:797487.Zora, H., Rudner, M., and Magnusson, A. (2020). Concurrent affective and linguistic prosody with the same emotional valence elicits a late positive ERP response. European Journal of Neuroscience,51, 2236–2249.