noise
WHAT is the most unpleasant, revolting or even horrific sound in the world?
Scientists from Newcastle University in the UK used 13 volunteers to test their reaction to 74 different noises to find out what sound humans find most unpleasant and pleasant.
Fingernails on a chalkboard, screeching tires and the sound of an animal dying were among the favourites.
But the tests discovered that a sharp knife scraped against a glass bottle was the most unpleasant, The Guardian in the UK reported.
Following up that unpleasant screech - think of the sound of a knife trying to get the last drop of jam from a jar - is a fork on glass. Then the almost redundant practice of chalk on a blackboard, a ruler on a bottle and fingernails on a blackboard (also no longer commonplace in our society).
The tests were designed to see the reactions both in outward response and more closely via small changes in the brain.
The worst noises have one thing in common: the sounds falls within the frequency range of 2,000 to 5,000 Hz, the same range that includes human screams, which our brains clearly dislike.
'If you have a sound in this frequency band it produces a heightened response. The ear is very sensitive in this acoustic spectrum,' said the paper's author Dr Sukhbinder Kumar. 'Although there is still much debate about why this should be, it does include animal warning calls and screams which we find intrinsically unpleasant.'
The most pleasant of the 74 sounds were applause (the least unpleasant), a baby laughing, thunder and water flowing.
The study was funded by the Wellcome Trust, with the findings published in the Journal of Neuroscience.
Dr Kumar said sounds could be unpleasant in two ways - because of their intrinsic nastiness or because of their associations, even though the sound itself might not be intrinsically unpleasant. An alarm clock may come to be hated not for its insistent ring but because it disturbs sleep.
The reason a scream makes us shiver is that the sound triggers an emotional reaction through the linkage between the auditory cortex and the amygdala. The emotional part of the brain takes charge of the auditory part so that our perception of a highly unpleasant sound, such as a knife scraped on a bottle, is heightened compared to a soothing sound such as babbling water.
Dr Kumar said a better understanding of the brain’s reaction to noise could help in the treatment of people with a decreased tolerance of sound such as hyperacusis, misophonia (hatred of sound) and autism when there is sensitivity to noise.
Professor Tim Griffiths of Newcastle University, who led the study, said: 'This work sheds new light on the interaction of the amygdala and the auditory cortex . This might be a new inroad into emotional disorders and conditions like tinnitus and migraine in which there seems to be heightened perception of the unpleasant aspects of sounds.'
Hear the worst sounds:
Originally published as Listen: The most unpleasant sounds
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