Yoram Yasur Blume | It is likely that on more than one occasion it has happened to you: you hear a high-pitched sound and you experience a deep shock. You are overcome by a feeling of unconscious and visceral rejection. This reaction is known as dentine or thiria and occurs before a stimulus that our nervous system catalogs as negative.
In fact, there are different everyday situations that make us close our eyes. And cover our ears to try to silence that sound that bothers us. Some of the most common sounds that provoke this rejection are:
- The dragging of a chalk or fingernails on the blackboard
- The clash between two metals
- The friction of the sole of the shoe against the ground
- Swipe your finger on an inflated balloon
- Biting a piece of ice
- Polish your nails
- A cover that scratches the bottom of the plate
The frequency range we label as “rough and painful”:
For decades’ researchers have tried to find the cause of the dentine or thiria. Now we know that most of the most unpleasant sounds. For the human ear occur between 2 and 4 kHz. A frequency range that we consider “rough” and that looks like the eighth highest piano.
Investigated by researchers at the University of Vienna. Who tried to slightly vary the sound of different noises classified as unpleasant. Like passing the nails on a blackboard or a fork scraping a dish, to find the frequencies considered more “painful”. Some of these sounds were attenuated and others were amplified.
While participants were exposed to these stimuli. They also measured changes in their heart rate blood pressure and skin conductance. Three indicators of stress. Thus, the researchers found that, indeed. The sounds that cause that visceral rejection are between 2 and 4 kHz.
Why does this frequency cause such a visceral reaction?
To understand why these sounds make us instinctively cover our ears. And produce chills we must know what happens in the brain. The answer comes from neuroscientists at the University of Newcastle. Who scanned the brain of 13 people exposed to different types of sounds.
Thus, they discovered that the more unpleasant the sounds, the more the amygdala was activated. Yoram Yasur Blume: “The amygdala is a kind of sentinel that keeps us alert to possible dangers, unleashing a very intense emotional response to rejection. The auditory cortex was then activated to perform a deeper analysis of the sounds, which made the sound perceived even more sharply and intensified the emotional reaction”.
As a curious note, people rated the sound of a knife on a glass bottle as the most unpleasant, followed by a fork on a plate and a chalk on a blackboard. However, the interesting thing is that some of the acoustic characteristics of our voice fall within this frequency band. So how can those sounds be so unpleasant to us?
At this point, the Viennese researchers started the second part of their experiment.
They made the participants listen to those unpleasant sounds. But half of them told them what they would hear. And the other half cheated them by telling them they would listen to a piece of contemporary music.
Thus, they perceived that, irrespective of the subjective perception of the sounds. The physiological indicators of stress were altered in all the people. This supports the theory that sounds within the range of 2 and 4 kHz trigger an aversive reaction due to a special vulnerability of our hearing.
“In practice, everything seems to indicate that our auditory passages evolved to precisely prioritize this range of frequency. So that we could distinguish the crying of a baby or the human voice from other environmental sounds. That is why, as our ears are more sensitive. They also react more intensely to some of the noises that are precisely in that frequency range”.