Fingernails on a chalkboard: If you shudder, here’s why…

In the classroom

Ms Fransisca wanted to teach her pupils some words to describe sounds. So she scratched her long fingernails on the chalkboard to elicit some answers.

Ms Fransisca: “I want all of you to think of a word as I scratch my nails on the board”.

Peter: “Ms Fransisca! I can only think of 3 words, MAKE IT STOP!”

Ms Fransisca : “Oops..that is not the expected answer! Peter are you alright?”

Peter: ” No definitely not. I just hate that sound!”

Peter runs around the classroom with his ears covered, together with some of his classmates, creating chaos.

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If you’re like Peter, you probably can’t stand the sound of fingernails scraping across a blackboard. Just the thought of it may even make you wince. This ear-piercing noise is so universally disliked, that it’s no surprise that many scientists have researched why it evokes such an instinctive reaction. There are many reasons to why one dislikes such noise.

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Shape of ear canals and own perceptions

Brain scans reveal that if we hear a sound that causes us to strongly suspect that another sound is on the way, the brain acts as if we’re already hearing the second sound. Similarly, if we see a certain collection of letters or words, our brains jump to conclusions about what comes next. Thus, the brain is able to preconceive the information. In this case, we use context to help us perceive.

For emaxlpe, it deson’t mttaer in waht oredr the ltteers in a wrod aepapr, the olny iprmoatnt tihng is taht the frist and lsat ltteer are in the rghit pcale. The rset can be a toatl mses and you can sitll raed it wouthit pobelrm.

In the paragraph above,  you probably didn’t get every single word right just from knowing what came before it. You may have thought that you were reading the passage perfectly, because you had naturally and subconsciously gone back and filled in any gaps in your knowledge based on subsequent context; the words that came later. Additionally, in this  example, where the words have jumbled middle letters, the brain is able to process all the letters of a word at once, rather than one at a time. Thus, the letters serve as contexts for each other.

Similarly, people are mainly affected by shrill noises because they already have a preconceived idea that they are annoying and bothersome. To some people, the thought alone of the sound that bothers them could also cause them to cringe.

The shape of the human ear canal may have evolved to amplify frequencies that are important for communication and survival. Thus, a painfully amplified chalkboard screech is just an unfortunate side effect of this mostly beneficial development.
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Unpleasant frequency range

From the research conducted, two sounds that were rated as the most unpleasant, among participants were,fingernails scratching on a chalkboard and a piece of chalk running against slate. The researchers then created variations of these two sounds by modifying certain frequency ranges. Half of the listeners were told the true source of the sounds while the other half were told that the sounds came from pieces of contemporary music. Then the new sounds were played for the participants, while  certain indicators of stress, such as heart rate, blood pressure and the electrical conductivity of skin were monitored.

It was found that the offensive sounds changed the listeners’ skin conductivity significantly.The most painful frequencies were not the highest or lowest, but instead those that were between 2,000 and 4,000 Hertz. The human ear is most sensitive to sounds that fall in this frequency range.

 

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Brain pickings

So what happens in the brain when one hears screechy sounds? Studies reveal that the fingernail-chalkboard sound triggers a rise communication between two regions of the brain, namely, the regions of the brain involved in hearing and emotions. The participants in this study were exposed to 74 different kinds of sounds, including nails scratching on a chalkboard. Functional magnetic resonance imaging(fMRI) was used to study the participants’ brain response to the sounds.

When the participants heard an unpleasant sound, there was an interaction between the auditory cortex, which processes sound, and the amygdala, which processes negative emotions. In addition to that, the more nasty the sound, the greater the activity between these two brain regions. Some of the most unpleasant sounds, based on the participants’ ratings, included a knife on a bottle, a fork on a glass and chalk on a blackboard. The nice and friendly sounds included flowing water, thunder and a laughing baby.

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Consolidation

Sounds that fall within the frequency range of 2000 to 4000 Hz are considered to be unpleasant. When these sounds are heard, there is a communication between the auditory cortex and amygdala. This communication, together with preconceived ideas about sounds and the evolution of the ear canal causes one to react with emotions such as a shudder upon hearing these sounds. Here are the top 10 annoying sounds for your enlightenment.

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References:

  1. http://www.personal.psu.edu/afr3/blogs/siowfa13/2013/10/the-sounds-that-make-you-cringe.html
  2. http://www.livescience.com/18392-reading-jumbled-words.html
  3. http://www.livescience.com/57106-why-fingernails-on-chalkboard-hurts.html

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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According to research, the most painful frequencies lie between 2,000 and 4,000 Hertz. The human ear is most sensitive to sounds that fall in this frequency range.

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4 thoughts on “Fingernails on a chalkboard: If you shudder, here’s why…

    1. 2000-4000Hz is the bandwidth for irritating sounds because our ears are most sensitive to sounds in that frequency range. This is due to the ‘roughness’ of frequency created by fluctuation of frequency that arises from sounds like nail scratching on board rather than sharpness of sounds due to high frequencies.

      Noise at high or low frequencies are thus not as annoying as it would be as when the energy is concentrated in the middle frequency of 2000-4000Hz.

      Like

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