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Health 123

Health 123 - Why does the sound of blackboard scratching drives people crazy?

Do you have such an experience, when you hear a nice song, the friction of a feather, the crisp sound of chewing potato chips or the sound of paper rubbing when turning a book? The whole body will have a numb sensation, an electric shock-like stimulus will start from the scalp and pass through the back of the neck and spine. The whole body’s hairs are erected by this unique stimulus, and the brain will also relax, stimulating a pleasant and refreshing feeling. . .

In fact this is called the ASMR, a very popular trend in recent years!
ASMR stands for Autonomous Sensory Meridian Response. In the process of an ASMR, our sensory, with the auditory, visual and tactile stimuli, make us feel relaxed, pleasant, calm, cosy, and even sleepy…

What then are those agitating and disturbing sounds to us?
For example, the sound of fingernails scratching the blackboard, the sound of styrofoam rubbing, the fork scraping the plate, etc..
If you were to make a comparison with those good experiences you have with an ASMR, are these sound causing you goosebumps all over your body and you find them just unbearable? Especially the sound of blackboard scratching with your fingernails? What is the exact reason behind it?

Human’s ears can hear sounds with frequency ranges between 20-20,000 Hz. Any sound that is lower or higher than this range, will not be captured by our ears.

Did you know? The sound of scratching the blackboard with fingernails has mounted to the top ten most annoying sound globally. Is it because the sound of scratching the blackboard with fingernails has produced a high frequency that it drives people crazy? 

Not so! In 1986, a German professor discovered that the most torturing sound frequency to human are not the highest or the lowest one, but those sound frequencies ranging between 2,000 and 4,000 Hz. Our ears would be the most sensitive to these frequencies, and the sound of fingernails scratching the blackboard falls exactly in this range of frequency. 

Some scientists speculate that the reason why we get agitated upon hearing the sound of fingernails scratching the blackboard is due to its sound frequency being similar to the cries of babies or the screaming of adults. These sounds are like alarms with a certain level of connection with “survival”.

At the same time, the shape of our acoustic meatus will enlarge certain sound frequencies after its evolution, causing pain to the ears. That is why when we hear such screeches, our ears will be in extreme pain. 

Another study published in the 2012 edition of The Journal of Neuroscience discovered that, when we hear all these undesired noises, they will stimulate two parts of our brain that are very sensitive to sound, i.e., the auditory cortex and amygdala that controls our negative emotions. These two parts become very active upon stimulation, leading to strong interactions between them. When the auditory cortex is stimulated by undesired sounds, and after it has sent these sound signals to the amygdala, it will provoke these negative emotions.
In return, it will stimulate the auditory cortex again, making us very uncomfortable, and hard to control our emotions. So, if you feel uncomfortable when you hear these sounds, just cover your ears before you lose control!