They make your teeth grate and the hairs stand up on the back of your neck but they may fulfil a vital role. Scientists have identified the acoustic world’s most unpleasant sounds and how they could help us to survive – by alerting us to danger.
Fingernails dragged across a blackboard and a fork scratching a glass were identified as among the nastiest noises in a study in which volunteers were asked to compare 74 sounds which included tyres screeching on a road, the wind whistling in the trees and a babbling brook.
When the volunteers were placed in an MRI scanner and told to rank the sounds in order of unpleasantness, the researchers found the worst noises provoked heightened activity in an area of the brain called the amygdala that controls emotion.
Sukhbinder Kumar of Newcastle University, author of the study, said: “There appears to be something very primitive kicking in. It is a possible distress signal from the amygdala to the auditory cortex.”
The most unpleasant sounds, as ranked by the 13 volunteers in the study, lay in the frequency range from 2000 to 5000 Hz which has been shown in previous studies to be the ear’s most sensitive area.
Dr Kumar said: “If you have a sound in this frequency band it produces a heightened response. The ear is very sensitive in this acoustic spectrum . 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 study was funded by the Wellcome Trust and the findings are 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.”
MOST UNPLEASANT SOUNDS
Rating 74 sounds, people found the most unpleasant noises to be:Reuse content