Most of us experience negative physiological reactions to certain sounds that send chills down the spine, such as fingernails scraping a chalkboard, squeaking Styrofoam, or cutlery scraping a plate.
If you have ever wondered why that is, research into this phenomenon has provided us with the scientific explanation.
A study conducted by Christoph Reuter of the University of Vienna, Musicological Institute and Michael Oehler of MHMK – University of Applied Sciences for Media and Communication, aimed to identify specific features that unpleasant sounds had in common to explain why we react in such a way.
They wanted to find out if there was a correlation between perception and the physiological reaction and also if being aware of the origins of the sound affects the subjects reaction to it.
First they carried out a listening test to determine the two most unpleasant sounds out of a range of several sounds that are commonly considered to be unpleasant. The two that topped the list were fingernails scratching a chalkboard, and squeaking chalk on a slate.
Variations of both sounds were produced by attenuating specific frequency ranges or extracting scraping components and tonal components. They asked the subjects to rate the sounds in terms of pleasantness or unpleasantness, while physiological parameters such as heart rate, galvanic skin response, and blood pressure were measured.
They split the group in half, with one half being aware of the origins of the sounds, and the other half told that they were hearing sounds taken from classical music.
The results showed that the most unpleasant sounds were those within the frequency range of 2000 Hz – 4000 Hz. When the frequencies within this range were attenuated the sounds were perceived as more pleasant. What is interesting is that the human ear is most sensitive to sounds around this frequency range, and many acoustic features of speech sounds are also found in this range.
One explanation given for the high sensitivity in this range is “open ear gain” meaning that some frequencies are amplified because of the shape of the ear canal.
Another effect observed was how pitch would influence perceived pleasantness. Sounds with deleted pitch information were considered to be more pleasant, whereas sounds with delete noise parts did not influence the ratings.
It was found that unpleasant sounds caused a greater difference in galvanic skin response from before the sound being played compared with during it.
If the subjects were aware of the origin of the sound the ratings tended to be more negative and the correlation between perception and galvanic skin response was stronger. Those who believed the sounds were taken from classical music tended to rate the sounds as more pleasant.
So based on these findings it was concluded that the acoustic characteristics of unpleasant sounds are found in pitch information and within the frequency range of 2000 Hz – 4000 Hz. These sounds invoke a physical reaction which is stronger when the listener is aware of the origin of the sound.
Do you react negatively to these kind of sounds? In case you are someone who actually enjoys the sound of fingernails on a chalkboard, here is a video for you: