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Halloween – why are some sounds scary?

Halloween is almost here and it’s a time when many of us enjoy scaring ourselves (and each other) with freaky carved pumpkins and creepy costumes. But why is it that we find certain sounds frightening?

It seems that science has the answer. Our brains have evolved over time to fear ‘non-linear’ sounds, which are sound waves with a high amplitude and a high volume. These types of sounds include frequency jumps, unusual harmonies or noise – which seem scary to us because they have a different pitch, frequency and volume when compared to our own vocal range. Because our brains have naturally evolved to understand that these sounds are abnormal, we react to them as potentially dangerous – essentially, our hearing acts as a survival mechanism.

Although certain sounds may frighten us, they are just vibrations – it is our brain’s reaction which causes our fears and triggers our own emotional response. As our brain processes sound a lot faster than visual information, we can assume that our sense of hearing evolved to become our first line of defence. Sounds that make us ‘jump’ are triggering our startle reflex to prepare us for a potential threat – even while we’re asleep.

Horror movies often include ‘non-linear’ sounds in order to scare the audience – such as sudden volume changes, clashing harmonies or screams. We feel scared due to our biology because we have evolved to understand that these sounds are potentially threatening. In fact, our sense of hearing travels through just five nerves before we react – and it occurs much faster than our brains can understand it! When we watch a scary movie, the music or soundtrack can make some of the visual scenes more terrifying – just by using shifting frequencies or abrupt volume changes.

Daniel Blumstein, Professor of Ecology and Evolutionary Biology at UCLA, studied the distress calls of marmots and discovered that they were characterised by ‘non-linear’ noise patterns. Interestingly, he also found this same pattern in the soundtracks of scary movies. According to Blumstein, noises and screams in these movies have the same effect on us as animal distress calls, in that they evoke strong feelings and emotions.

The use of minor chords and dissonant sounds in music can conjure a spooky atmosphere too. In the Middle Ages, a musical tritone became known as the “Devil’s interval”. For musicians, it refers to the augmented 4th – the interval between A and E flat or between D flat and G. The two notes that make up the “Devil’s interval” have incompatible wavelengths so instead of creating a regular pattern, they form a dissonant sound (you can find it in the opening violin chords of Saint Saens’ Danse Macabre.)

So if you watch a scary movie this Halloween, take note of the soundtrack or background noises. Does it make what you can see on-screen more emotive? Do the high-pitched screams, sudden noise and “Devil’s intervals” make you jump out of your seat? If you find the whole horror movie experience a bit overwhelming, simply turn off the sound – you’ll probably find that the film will appear much less terrifying…