Nasty noises and neuroscience

Chalk on a blackboard? A knife on glass? Even the thought of some of these sounds makes people squirm. In our office the topic sparked an instant discussion, everyone has an opinion as to what sounds really bother them. Unsurprisingly, fingernails on a blackboard were mentioned first, but so were nails on garage doors and teaspoons against the inside of mugs. But why do we get that spine tingling feeling with certain nasty noises for no obvious reason?

A new study reveals what we think of as the most unpleasant noises and what happens in our brains when we hear them. Researchers at the Wellcome Trust Centre for Neuroimaging at UCL and Newcastle University, had 13 volunteers listen to 78 unpleasant sounds while in an fMRI machine. They ranked the five nastiest noises as: 

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.

The fMRI scans showed a link between the area of the brain that processes emotions, the amygdala, and the auditory area, the auditory cortex. The researchers theorise that when we hear an unpleasant noise the amygdala regulates the response of the auditory cortex, in turn heightening its activity and provoking a negative reaction. In effect, the emotional part of the brain takes charge and decides upon the activity of the auditory part of our brain, increasing our perception of an unpleasant sound.

Our ears are most sensitive to sounds between 2000 and 5000 Hz and it was within this range that the unpleasant sounds fell. To put this in perspective, the highest note on a piano is 4096 Hz and the average human voice is around 200 Hz. A scream, which is intrinsically unpleasant, would fall in the range of 2000 to 5000 Hz.

Professor Tim Griffiths from Newcastle University, who led the study, says, “this might be a new inroad into emotional disorders like tinnitus and migraine in which there seems to be heightened perception of the unpleasant aspects of sounds”. As well as this, a better understanding of the brain’s reaction to noise could help our understanding of medical conditions where people have a decreased sound tolerance. For example, hyperacusis misophonia (literally a “hatred of sound”), and autism where a higher sensitivity to sound is often a symptom.

Although the study participants voted the five sounds above as their most unpleasant, a different group may have listed others. Having volunteered to listen to all of them for the sake of this post nails on a blackboard certainly does it for me. But, personally, the sounds themselves don’t bother me as much as the act of doing them. Scraping my own fingernails down a blackboard really would send a shiver down my spine.

Reference

• Sukhbinder, K., von Kriegstein, K., Friston, K., & Griffiths, T (2012). Features versus Feelings: Dissociable Representations of the Acoustic Features and Valence of Aversive Sounds. The Journal of Neuroscience32(41):14184 –14192, 32 (41), 14184-14192 DOI: 10.1523/JNEUROSCI.1759-12.2012

Image Credit: Flickr. Nails on a Chalk Board

http://www.flickr.com/photos/dolmansaxlil/5187733253/