Neuroscientists at the Swiss Federal Institute of Technology in Lausanne (EPFL), the University Hospital of Lausanne and the University of Lausanne have discovered a strange bias in our perception of pleasant sounds.
According to brain scans of 13 adults, positive human sounds such as laughter lead to stronger neural activity in the brain’s auditory system when heard from the left side, indicating that the human auditory cortex is specifically tuned to direct the sounds that make us happy. And it is not clear why there was a preference at all – the experiments were focused only on changing the activity in the auditory cortex. How such a change affects someone’s perception of these sounds is unknown and will need to be tested in future studies.
However, previous research has shown that the left ear can more easily detect the emotional tone in someone’s voice, indicating some hidden specialization.
Since the left ear relays information to the right side of the auditory cortex first, he hypothesized that the right hemisphere of the brain is better at processing emotions than the left.
But these latest results show that this may not be the correct answer.
And when study participants listened to happy human sounds from three different directions—left, center, or right—both sides of the auditory cortex were activated.
However, the recordings listened to only on the left side elicited a much stronger nervous reaction.
Neuroscientist Sandra Da Costa of EPFL says: “This doesn’t happen when the positive sounds come from the front or the right. We also show that sounds with neutral or negative emotional valence, such as meaningless vowels or screams of terror, and sounds other than voices. Humanity is not tied to the left side.”
Obviously the direction of the noise can affect the quality of this sound – imagine an ambulance siren moving towards you and then moving away. It can also affect our perception.
Previous research has shown that approaching sounds are often perceived as more dangerous and disturbing than receding sounds. Evidence suggests that a person is more easily aroused when the sound comes from behind.
Heightened sensitivity to certain sounds coming from certain directions has a wide evolutionary significance. No doubt human survival in past millennia would have depended on greater suspicion of voices coming from behind.
But the Left’s propensity for emotion in the human voice is not so easy to explain.
It is known that some brain functions are more associated with the left hemisphere than with the right, and vice versa, but in this particular case, this does not seem to explain the results.
And although the right hemisphere of the auditory cortex showed a stronger response to joyful human sounds in one area called L3, in the experiments, the sounds activated both hemispheres of the brain.
Neuroscientist Stephanie Clark says: “It is currently unknown when the primary auditory cortex prefers positive human vocalizations to the left during human evolution, and whether this is a unique human trait. Once we understand this, we can speculate whether this is due to a preference for a manual or non-left position, which is equivalent to internal organs.
The study is published in the journal Frontiers. in Neurology.
Source: Science Alert
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