2000 – 5000 Hz, the frequency range of sounds which humans find most unpleasant. At least according to new research from Newcastle University.
It’s worth noting that the participants in the study were asked to rate a series of sounds according to how ‘unpleasant’ they were. A subjective term that brings semantics into an otherwise rigid body of research.
After all, for some, the constipated strain of Adele grasping for ‘don’t forget me, I beg’ on ‘Someone Like You’ is pleasant enough to fuel last year’s £41.7m profit at XL Records (announced today). Mariah Carey’s ability to hit G#7 (3250 Hz) is, apparently, part of her appeal. For others, the effect ranks in unpleasantness alongside self-administered ritual circumcision.
The wording is significant, and the sound ranges are substantially higher in frequency than the usual benchmark of 500 Hertz (the standard pitch of a baby’s cry) that crops up most often in studies pertaining to human sound/response theories.
“It appears there is something very primitive kicking in,” says Dr Sukhbinder Kumar, the paper’s author from Newcastle University. “It’s a possible distress signal from the amygdala to the auditory cortex.”
But what exact danger the message conveys is open to speculation. Although the human voice can reach the ranges mentioned, the 2000-5000 Hz values correspond to the highest soprano notes. Towards the upper limit, the harmonics of a scream are the most likely reason for a voice to reach such a pitch.
Unpleasant, certainly. But hardly a response destined to mobilise the tribe for fight/flight reactions. Perhaps it was just a way to clear some space in the cave.
The worst noises in the world: Why we recoil at unpleasant sounds
In a study published in the Journal of Neuroscience and funded by the Wellcome Trust, Newcastle University scientists reveal the 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.
Brain imaging has shown that when we hear an unpleasant noise the amygdala modulates the response of the auditory cortex heightening activity and provoking our negative reaction.
[box] It appears there is something very primitive kicking in[/box]
“It appears there is something very primitive kicking in,” says Dr Sukhbinder Kumar, the paper’s author from Newcastle University. “It’s a possible distress signal from the amygdala to the auditory cortex.”
Researchers at the Wellcome Trust Centre for Neuroimaging at UCL and Newcastle University used functional magnetic resonance imaging (fMRI) to examine how the brains of 13 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.
Researchers found that 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.
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 explains: “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.”
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, says: “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.”
MOST UNPLEASANT SOUNDS
Rating 74 sounds, people found the most unpleasant noises to be:
1. Knife on a bottle
2. Fork on a glass
3. Chalk on a blackboard
4. Ruler on a bottle
5. Nails on a blackboard
6. Female scream
7. Anglegrinder
8. Brakes on a cycle squealing
9. Baby crying
10. Electric drill
LEAST UNPLEASANT SOUNDS
1. Applause
2. Baby laughing
3. Thunder
4. Water flowing
Source: Newcastle University
Image: Idea go/FreeDigitalPhotos.net
The aim of art is to represent not the outward appearance of things, but their inward significance. – Aristotle
