Researchers 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 to the most pleasing. Scientists were then able to study the brain response to each type of sound and they believe they have found 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. 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.
"It appears there is something very primitive kicking in," says Dr. Sukhbinder Kumar of Newcastle University. "It's a possible distress signal from the amygdala to the auditory cortex."
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. 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.
So what did they rate as the worst sounds? Oddly, it was not those fingernails on blackboards, but we have linked to the worst 5 so you can enjoy as well:
MOST UNPLEASANT SOUNDS
Rating 74 sounds, they determined the most unpleasant sounds were:
6. Female scream
8. Brakes on a bicycle squealing
9. Baby crying
10. Electric drill
LEAST UNPLEASANT SOUNDS
2. Baby laughing
4. Water flowing
So glass showed up three times and chalkboards only twice. Here's betting if the test subjects had to use their own fingernails on that chalkboard it would have shot to a unanimous number one.
No surprise applause showed up as number one. You should give yourself a round if you listened to all five of those unpleasant noises. Does it make a difference if you are creating the noises?