Scientists draw up league of world’s worst noises

Scratching blackboards, scraping plates and the screech of tyres: according to a new study, these are the world’s nastiest noises. Why do we find them so excruciating?

One knife, one fork and an empty glass – a freshly laid table, or the ingredients for a session of aural agony?

Researchers who measured and ranked the mental effects of 74 everyday noises have found that the most horrible of them all is produced by cutlery scratched across glass. The noise of nails or chalk being scraped across a blackboard follows close behind.

Unsurprising, perhaps. But this was not just an exercise in gathering trivia. It was a serious scientific study whose aim, using MRI scans, was to uncover the effects of sound on the human brain.

The results are clear: sounds are tightly linked to emotions. The auditory cortex, the part of the brain responsible for processing sound, is physically connected to another region that triggers negative feelings. When a nasty noise makes you wince or ‘sets your teeth on edge’, primitive biological processes are at work.

Why these specific sounds cause such an intense reaction is not certain, but one probable factor is their frequency: all of the five worst sounds have a similarly screechy pitch. Why are humans so distressed by high noises?

It may be partly a matter of health. Sounds that resonate at certain high frequencies are amplified by the shape of our ear canal so that they become loud enough to cause us pain, and potentially damage. Our cringing reaction to fingers on a blackboard may simply be a warning from the brain to get away from the harmful noise.

But there may also be evolutionary reasons. The frequencies of these sounds are similar to those of a human scream – and also very close to the alarm calls of certain higher apes with whom we share a common ancestor. It is possible that certain noises awake in us a useful instinct of fear and discomfort that predates modern humans.

It is not just bad noises that illicit such deep-seated reactions. Scientists have also found that revolting tastes, dirt and even perceived injustice can awake similar instinctive reactions. Primitive feelings of disgust may hold sway not only over our feelings and preferences, but even over our moral judgements.

Inner ear

Rationalists are disturbed by this suggestion. If human reactions are based on primitive senses rather than logic and reason, they say, we are no better than apes. If we hope to master ourselves or achieve anything worthwhile, we must free our intellect from these unthinking, animal instincts.

But others believe that these leftovers from our distant past are a valuable inheritance. A gut reaction can help us to make decisions that are much harder to arrive at through rational thought, they say. Instead of suppressing our instincts, we should nurture and respect them.

You Decide

  1. What is the worst sound in the world? What is it that makes it so horrible?
  2. Should we listen to our instincts or ignore them?

Activities

  1. Design an experiment to find out the world’s most pleasant sound. Write a hypothesis, then explain the methods you would use and how you would ensure your results were fair and accurate.
  2. Draw a diagram to show how the sound of someone scraping their fingers on a blackboard travels through the human ear.

Some People Say...

“The best noise in the world is the sound of silence.”

What do you think?

Q & A

Screechy sounds are unpleasant – I already knew that. So what’s the point of this big, complicated experiment?
Scientists often ask questions that we think we know the answer to. But that doesn’t make them a waste of time. For a start, the results often defy conventional knowledge. In this study, for instance, participants were played sounds without knowing their source. If they had had no objection to a scratching sound unless they knew it was produced by nails on a blackboard, that would have shown our reactions are shaped by culture.
But it didn’t.
That is valuable information in itself. But the study also achieved other things: it tracked the way in which we process horrible sounds, and gathered them together so that they can be analysed for shared characteristics. This could tell us much about our senses and brains.

Word Watch

Aural
Literally ‘of the ear’ – usually to do with sound or hearing. Not to be confused with ‘oral’, which means ‘of the mouth’ and relates to speaking.
MRI scans
Magnetic Resonance Imaging is a way of detecting and visualising internal processes in the body by creating a magnetic field around certain particles. It is particularly useful in analysing brain activity, muscles and cancers.
Frequency
Sound is created when particles vibrate in the air, passing on energy from one particle to the next. These vibrations can be mapped as waves. A sound’s ‘frequency’ is controlled by how long each wave is (its ‘wavelength’). This is the most important factor in determining whether the sound is high or low. All animals can hear sounds only when they fall within a particular wavelength, including humans.
Amplified
The middle ear (the first section of your ear beyond the visible part) contains three bones that help to amplify sounds that enter it – that is, to make them louder. These are scientifically known as the malleus, the incus and the stapes, but often called hammer, anvil and stirrup. However, if they are amplified too much, noises can cause damage to the sensitive inner ear.
Alarm calls
Many animals emit specific noises to warn other members of their species of threats, such as predators. In apes, these can be complex and minutely adapted.

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