(Newswire.net — February 13, 2017) —
Like most people, you probably cannot stand the screeching sound that fingernails make when scraped on a blackboard. This particular ear piercing noise is universally disliked and reason why numerous scientists have been researching on it for decades now.
So why is this particular sound so hateful and evokes such a visceral reaction?
Overall, research indicated that the ear splitting blackboard scraping noise had the same frequency of that of a human or a baby’s scream and are linked to survival. The first research conducted at Northwestern University in 1986 tested the sound frequencies of blackboard scraping by first removing some of the higher frequencies from the recordings and then the middle and the lower ones respectively. The scientists then asked the subjects to rate a series of various sounds such as Styrofoam squeaking and fork scraping on a plate along with blackboard scraping based on the unpleasantness they exuded. It was observed that the rate of unpleasantness was decreased when the middle or lower frequencies were removed as against the higher ones.
The psychoacoustics researchers further created variations in the sounds by modifying the frequencies and primarily removing the harmonic and concordant tones. The sources of these sounds were divulged to half of the subjects while the other half were informed that the sounds were extracted from various pieces of contemporary music. The new sounds were finally played to both the parties while the scientists monitored certain stress indicators such as blood pressure, heart rate and the skin’s electrical conductivity.
It was observed that the offensive frequencies were not the highest or the lowest ones, but the ones which were between 2000 and 4000 hertz and typically caused pain in the human ear. Researchers pointed out that the human ear is the most sensitive to the sounds which fall within this range of frequency. It might just happen that the shape of the human ear canal has evolved over a time in such a way that it amplifies frequency which is beneficial for survival and communication. Therefore, a painful screeching of blackboard scraping is only an unfortunate side of this evolution.
In this research the subjects who were informed that the sounds were specifically collected from musical instruments rated the frequencies as more pleasant than the subjects who were informed that the sound was collected from random sources. However the skin conductivity of the subjects in both the groups expressed identical conductivity. Hence it can be deduced that blackboard screeching may not irk people so much as much if they did not already know the source.
In 2012, another study revealed that the series of changes which occur in the human brain when they are exposed to unpleasant sounds. This research, published in the Journal of Neuroscience pointed out that the sound of fingernails scraping on a blackboard triggers a distressed signal between the region of hearing in the brain i.e. the auditory cortex and the region which processes negative emotions i.e. amygdala.
Although there is still much debate over the reason for the unpleasant sensitivity that blackboard scraping creates, it is imperative that,
- This irksome sound frequency intrinsically evokes the negative emotions in our brain.
- More than the generation of negative emotions, it is the thought (or the knowledge) of the fingernails scraping on the blackboard which makes the experience all the more unpleasant.
With the fast replacement of blackboards with whiteboards in schools and various academic institutions, let us hope that we will be able to put this universal unpleasantness at the back of our mind soon.