Summary: Positive human voices, such as laughter, coming from the listener’s left side elicit stronger activity in the auditory cortex of the brain.
The researchers used functional magnetic resonance imaging (fMRI) to observe the brain’s response to different types of sounds from different directions in right-handed participants. They observed the highest activation in the primary auditory cortex when participants listened to positive vocalizations coming from the left, compared to the front or right.
This finding may imply that the nature, emotional valence, and spatial origin of a sound are initially processed in the primary auditory cortex.
Key facts:
- Positive human sounds, such as laughter, coming from the left side lead to stronger activity in the brain’s auditory cortex.
- This strong activation due to sounds with positive emotional valence occurs in the primary auditory cortex of each cerebral hemisphere.
- The brain’s apparent preference for left-sided positive vocalizations has yet to be explained in terms of its evolutionary significance or emergence during human development.
The sounds we hear around us are physically determined by their frequency and amplitude. But for us, sounds have meaning beyond these parameters: we can perceive them as pleasant or unpleasant, ominous or soothing, interesting and informative, 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 approaching sounds moving toward them as more unpleasant, powerful, arousing, and intense than receding sounds, and especially if they come from behind rather than from the front.
This bias may have a plausible evolutionary advantage: for our ancestors on the African savannah, a sound approaching from behind their vulnerable backs may have signaled a stalking predator.
Now neuroscientists from Switzerland have shown another effect of direction on emotional valence: we respond more strongly to positive human sounds, such as laughter or pleasant vocalizations, when they come from the left.
“Here we show that human vocalizations that evoke positive emotional experiences elicit strong activity in the auditory cortex when coming from the listener’s left side. This does not happen when the positive voices come from the front or the right,” said first author Dr. Sandra da Costa, research fellow at EPFL in Lausanne, Switzerland.
“We also show that vocalizations with neutral or negative emotional valence, such as nonsense vowels or frightened screams, and sounds other than human vocalizations do not have this association with the left side.”
From erotic vocalizations to a ticking bomb
Da Costa and his colleagues used functional magnetic resonance imaging (fMRI) to compare how strongly the brains of 13 volunteers responded to sounds coming from the left, front, or right.
They were women and men in their mid-twenties, all right-handed and none trained in music.
The researchers compared the brain’s response between six categories of sounds: in addition to positive human vocalizations such as erotic sounds, they reproduced neutral and negative vocalizations, such as nonsense vowels and frightened screams; and positive, neutral, and negative nonvocalizations, such as clap, wind, and ticking bomb.
From the shore et al. focused on brain areas known to be important for the early stages of sound processing, primary auditory areas A1 and R, surrounding other early auditory areas and the ‘vocal area’ (VA). Each of these areas is located in the left and right hemispheres of the brain.
The results showed that A1 and R in both hemispheres became maximally active when listening to positive vocalizations coming from the left, and much less when listening to positive vocalizations coming from the front or right, to neutral or negative vocalizations or non-vocalizations.
Auditory cortex discriminates in favor of positive vocalizations on the left
“Strong activation by vocalizations with positive emotional valence coming from the left takes place in the primary auditory cortex of each hemisphere: the first areas in the cerebral cortex to receive auditory information.
“Our findings suggest that the nature of the sound, its emotional valence and its spatial origin are first identified and processed there,” said co-author Dr. Tiffany Grizendi.
In addition, area L3 in the right hemisphere, but not its twin in the left hemisphere, also responded more strongly to positive vocalizations coming from the left or right compared to those coming from the front. In contrast, the spatial origin of the sound did not affect the non-vocalization response.
The evolutionary significance of our brain’s bias in favor of positive vocalizations coming from the left is still unclear.
Senior author Prof. Stephanie Clark, from the Neuropsychology and Neurorehabilitation Clinic at the University Hospital of Lausanne, said: “It is currently unknown when the preference of the primary auditory cortex for left-sided positive human vocalizations emerges during human development and whether this is a uniquely human characteristic.
“Once we understand that, we can speculate whether it’s related to hand preference or the asymmetric placement of internal organs.”
About this auditory neuroscience research news
Author: Misha Dijkstra
source: Borders
Contact: Misha Dijkstra – Borders
Image: Image credited to Neuroscience News
Original Research: Free access.
“Emotional sounds in space: asymmetric representation in early auditory areas” by Sandra da Costa et al. Frontiers in Neuroscience
Summary
Emotional sounds in space: asymmetric representation in early auditory areas
Evidence from behavioral studies suggests that the spatial origin of sounds can influence the perception of emotional valence.
Using 7T fMRI, we investigated the influence of sound categories (vocalization; non-vocalization), emotional valence (positive, neutral, negative), and spatial origin (left, center, right) on encoding in early auditory areas and in the voice region.
The combination of these different features resulted in a total of 18 conditions (2 categories x 3 valences x 3 lateralizations), which were presented in a pseudorandomized order in blocks of 11 different sounds (from the same condition) in 12 different 6-min runs. In addition , two localizers, i.e. tonotopic mapping; human vocalizations, were used to define regions of interest.
A three-way repeated-measures ANOVA of BOLD responses revealed two-way significant effects and interactions in primary auditory cortex, early lateral auditory areas, and vocal tract.
Positive vocalizations presented on the left side elicited greater activity in ipsilateral and contralateral primary auditory cortex than neutral or negative vocalizations or any other stimuli at any of the three positions.
Right but not left L3 area responded more strongly to (i) positive vocalizations presented ipsi- or contralaterally than to neutral or negative vocalizations presented at the same positions; and (ii) to neutral by positive or negative nonvocalizations presented contralaterally.
Moreover, comparison with a previous study shows that spatial cues can make emotional valence more salient in early auditory areas.
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