Why some people hear the sound of fingernails scraping on a blackboard manic?(1)

  In life, there are all kinds of weird sounds make us feel crazy, like fingernails across a blackboard, chalk across the blackboard of the moment, the sound of drill, bicycle brakes, knife across the cup……Why some people hear the sound of fingernails scraping on a blackboard manic?  These sounds make us feel uncomfortable, anxious and want to avoid them……So the question is, why do some voice makes us very uncomfortable, very crazy, very upset it?  We usually hear the sound vibrations are generated by, just like a wave, spread through the air and other media。
Here we must explain how these sounds make us uncomfortable key – Hertz, which is the number of times within one second body vibration, such as 1000 Hz, is a second shock of 1000 that humans can hear the sound range is 20?20000 Hz, not within the scope of sound waves are not receiving our ears, but the nature of some animals but they can, for example, rely on ultrasound to locate the bats and dolphins。  Then we heard those bicycle brakes, etc. These sounds uncomfortable because of the frequency of these sounds are too high yet?Well, not exactly。
As early as 2011, the German university professor 麦科米迪亚 MichaelOehler, who had done special tests, We are only between 2000 Hz to 4000 Hz frequency range unbearable sound。
After they recorded the sound of fingernails scraping a blackboard, repeated testing, but no matter remove high frequency or low frequency part of the sound is still cacophonous, only after the partial removal of the middle, it sounds comfortable。
  In 2012, researchers at Newcastle University SukhbinderKumar, who not only re-test the scope of these sounds, but also tested when we hear these sounds, our brain activity。
The results showed that, when we hear these sounds, the brain cortex and amygdala Contact About hearing significantly enhanced。
Here that the amygdala is not the kind we eat, but the emotional response centers of the brain, if we amygdala activity too active, then people are likely unable to control their emotions, so it was a baffling to hear this voice gas is not one to play。  And some people would feel after hearing the whole body tingling, chills backbone of the reasons is because of this unbearable sound after wear as our ears can cause us significant physiological stress response, there is a cold body hair Ma symptoms。  In fact, we usually should have heard some say: because these sounds like our original ancestors of the warning sound, through genetic memory passed down from generation to generation, so that we will have a clear response to this sound。
In fact, most scientists think so, warning sound gorilla, and we scream and these sounds are similar, but when the animal or human to survive, just need companions to hear their own voice, so now there are many scientists agree that this terrible noise and survival are closely related。  In general, the moment when the nail across the blackboard, an acoustic wave generated at each frequency, but mainly in the 2000Hz?Between 5000Hz, which sound waves are passed through the air to our eardrum, the eardrum produces vibrations corresponding to this step up is the problem of physics。
  And when these sound frequencies of the auditory nerve to the brain, we feel uncomfortable it is a matter of biology, now scientists have explained that these sounds are closely related to human survival, and we are very sensitive to this human in order to survive over the long-term evolution of the results。

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