The next time you whisper sweet nothings in someone’s ear, you might want to aim for their left side.
Neuroscientists from the Swiss Federal Institute of Technology Lausanne (EPFL), the University Hospital of Lausanne and the University of Lausanne in Switzerland have discovered a strange bias in our perception of pleasant voices.
According to the brain scans of 13 adults, positive human sounds, such as laughter, cause stronger neural activity in the brain’s auditory system when heard from the left side, suggesting that the human auditory cortex is specially tuned to the direction of sounds that make us happy.
Why there is a preference at all is not clear – this experiments focused only on changes in activity in the auditory cortex. How such a change translates into one’s perception of those sounds is unknown and should be tested in future research.
That being said, previous studies have shown that the left ear can more easily recognize the emotional tone in a person’s voice, suggesting an underlying specialization.
Since the left ear sends information to the right hemisphere of the auditory cortex first, it was believed that the right side of the brain must be better able to process emotions than the left.
But these recent results suggest that may not be the right answer.
When the study participants listened to happy human vocalizations from three different directions — left, center, or right — both sides of their auditory cortex were activated.
However, recordings heard only on the left side elicited a much stronger neurological response.
“This doesn’t happen when positive vocalizations come from the front or the right,” say neuroscientist Sandra da Costa of EPFL.
“We also show that vocalizations with neutral or negative emotional valence, for example meaningless vowels or fearful screams, and sounds other than human vocalizations, do not have this association with the left side.”
The direction of a sound can of course affect the quality of that sound – think of an ambulance siren driving towards you and then away. And it can also affect our perception.
Last studies have shown that looming sounds are often perceived as more ominous and exciting than receding sounds. And proof suggests a person becomes aroused more easily when a sound comes from behind.
Increased sensitivity to certain sounds coming from certain directions has broad evolutionary significance. The survival of a human being in past millennia would no doubt depend on additional distrust of sounds creeping up from behind.
But a left-handed preference for the emotion in human voices is not so easily explained.
Some brain functions are known to be more on the left side of the brain than the right side, and vice versa, but in this particular case that doesn’t seem to explain the results.
While the right hemisphere of the auditory cortex showed a stronger response to happy human voices in a region called L3, both hemispheres were activated by the sounds in experiments.
“It is currently unknown when the primary auditory cortex’s preference for positive human vocalizations from the left appears during human development, and whether this is a uniquely human trait,” say neuroscientist Stephanie Clarke.
“Once we understand this, we can speculate whether it is related to hand preference or the asymmetrical arrangement of the internal organs.”
The study is published in Frontiers in neuroscience.