A woman supporter of a Pakistani religious group 'Minhaj-ul-Quran' shouts anti Taliban slogans during a demonstration in favor of 14-year-old schoolgirl Malala Yousufzai, who was shot on Tuesday by the Taliban, Saturday, Oct. 13, 2012 in Islamabad, Pakistan. Pakistan police have arrest a number of suspects in the case of Yousufzai shot and wounded by Taliban for promoting education for girls and criticizing the fundamentalist Islamic movement, officials said.Photo/Anjum Naveed)
The first-of-its-kind study conducted by researchers at Newcastle University has ranked the sound of a knife on a bottle, fork on a glass and chalk on a blackboard as the top three unpleasant sounds in a list of 74.
A baby crying or an electrical drill also figures in this list of unpleasant sounds.
On the other hand, the crackling of thunder or the sound of flowing water are among the least unpleasant.
In a study published on Sunday in the Journal of Neuroscience, and funded by UK's Wellcome Trust, Newcastle University scientists said there was an interaction between the region of the brain that processes sound, the auditory cortex, and the amygdala, which is active in the processing of negative emotions when we hear unpleasant sounds.
This, they said, explained why humans shriek at unpleasant sounds.
Researchers said that brain imaging had shown that "when we hear an unpleasant noise, the amygdala modulates the response of the auditory cortex heightening activity and provoking our negative reaction."
Dr Sukhbinder Kumar, the paper's author from Newcastle University, said, "It appears there is something very primitive kicking in. It's a possible distress signal from the amygdala to the auditory cortex."
Researchers at the Wellcome Trust Centre for Neuroimaging and Newcastle University used functional magnetic resonance imaging (fMRI) to examine how the brains of volunteers responded to a range of sounds.
Listening to the noises inside the scanner, they rated them from the most unpleasant -- the sound of knife on a bottle - to pleasing, bubbling water. Researchers were then able to study the brain response to each type of sound.
"The activity of the amygdala and the auditory cortex varied in direct relation to the ratings of perceived unpleasantness given by the subjects. The emotional part of the brain, the amygdala, in effect takes charge and modulates the activity of the auditory part of the brain so that our perception of a highly unpleasant sound, such as a knife on a bottle, is heightened as compared to a soothing sound, such as bubbling water," the researchers said.
Analysis of the acoustic features of the sounds found that anything in the frequency range of around 2,000 to 5,000 Hz was found to be unpleasant.
Dr Kumar explained, "This is the frequency range where our ears are most sensitive. Although there's still much debate as to why our ears are most sensitive in this range, it does include sounds of screams which we find intrinsically unpleasant."
Experts say that scientifically, a better understanding of the brain's reaction to noise could help our understanding of medical conditions where people have a decreased sound tolerance such as hyperacusis, misophonia (literally a hatred of sound) and autism when there is sensitivity to noise.
Professor Tim Griffiths from 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 disorders like tinnitus and migraine in which there seems to be heightened perception of the unpleasant aspects of sounds."
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