The 10 most annoying sounds - and why they bother us so much

Fingernails on a chalkboard, electric drills, wailing babies -- in a new study, scientists identified these as among the ten most annoying sounds to the human ear, as well as finding clues as to why they send shivers down our spine.

When people hear an annoying noise, a part of the brain that regulates emotions, called the amygdala, seems to take over the hearing part of the brain, researchers say.

"It appears there is something very primitive kicking in," says researcher Sukhbinder Kumar of the Institute of Neuroscience at Newcastle University in Newcastle upon Tyne, UK. "It's a possible distress signal from the amygdala to the auditory cortex."

The results of the study suggests that a heightened emotional response in the brain to certain noises can alter our perception of them.

In the study, 13 volunteers responded to a range of sounds while their brains were scanned using functional magnetic resonance imaging (fMRI). Analysis of the acoustic features of the sounds revealed that noises in the frequency range of around 2,000 to 5,000 Hz were found to be unpleasant.

"This is the frequency range where our ears are most sensitive," said Kumar. "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."

Researchers identified these as the most unpleasant sounds:

1. Knife on a bottle
2. Fork on a glass
3. Chalk on a blackboard
4. Ruler on a bottle
5. Nails on a chalkboard
6. Female scream
7. Angle grinder
8. Brakes on a cycle squealing
9. Baby crying
10. Electric drill

The study also identified some of the least unpleasant sounds:

1. Applause
2. Baby laughing
3. Thunder
4. Water flowing

The study was published last week in the Journal of Neuroscience.