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hubie [soylentnews.org] writes:

This bias can be explained by the way our brain is organized, but its evolutionary significance is not yet known [frontiersin.org]:

Sounds that we hear around us are defined physically by their frequency and amplitude. But for us, sounds have a meaning beyond those parameters: we may perceive them as pleasant or unpleasant, ominous or reassuring, and interesting and rich in information, or just noise.

One aspect that affects the emotional 'valence' of sounds – that is, whether we perceive them as positive, neutral, or negative – is where they come from. Most people rate looming sounds, which move towards us, as more unpleasant, potent, arousing, and intense than receding sounds, and especially if they come from behind rather than from the front. This bias might give a plausible evolutionary advantage: to our ancestors on the African savannah, a sound approaching from behind their vulnerable back might have signaled a predator stalking them.

Now, neuroscientists from Switzerland have shown another effect of direction on emotional valence: we respond more strongly to positive human sounds, like laughter or pleasant vocalizations, when these come from the left. The results are published in Frontiers in Neuroscience [frontiersin.org].

"Here we show that human vocalizations that elicit positive emotional experiences, yield strong activity in the brain's auditory cortex when they come from the listener's left side. This does not occur when positive vocalizations come from the front or right," said first author Dr Sandra da Costa, a research staff scientist at the EPFL in Lausanne, Switzerland.

"We also show that vocalizations with neutral or negative emotional valence, for example meaningles vowels or frightened screams, and sounds other than human vocalizations do not have this association with the left side."

[...] The evolutionary significance of our brain's bias in favor of positive vocalizations coming from the left is still unclear.

Senior author Prof Stephanie Clarke, at the Neuropsychology and Neurorehabilitation Clinic at the Lausanne University Hospital said: "It is currently unknown when the preference of the primary auditory cortex for positive human vocalizations from the left appears during human development, and whether this is a uniquely human characteristic. Once we understand this, we may speculate whether it is linked to hand preference or the asymmetric arrangements of the internal organs."

Journal Reference:
Tiffany Grisendi, Stephanie Clarke and Sandra Da Costa, Emotional sounds in space: asymmetrical representation within early-stage auditory areas [open], Front. Neurosci., 19 May 2023, Volume 17 - 2023 | https://doi.org/10.3389/fnins.2023.1164334 [doi.org]

Original Submission