Pointed ear on cosplayer at the Amphi festival 2017

Sound direction influences our response

The sounds we hear are defined by their frequency and amplitude. However, we interpret sounds in a way that goes beyond these physical characteristics. We may find them pleasant or unpleasant, reassuring or ominous, interesting and informative, or just noise.

The source of a sound affects how we perceive its emotional ‘valence’, or whether we perceive it as positive, neutral, or negative. Generally, people tend to rate sounds that approach them, or ‘looming’ sounds, as more unpleasant, potent, arousing, and intense than sounds that move away from them, or ‘receding’ sounds. This is especially true if the sound comes from behind, as opposed to the front. This bias might have provided an evolutionary advantage to our ancestors on the African savannah, as a sound approaching from behind could signal a predator stalking them.

Stronger response to positive sounds coming from the left

Neuroscientists from Switzerland found that the direction of human sounds affects our emotional response. Positive sounds, such as laughter or pleasant vocalizations, elicit a stronger response when coming from the left.

Dr Sandra da Costa, a research staff scientist at the EPFL in Lausanne, Switzerland, said,

“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.”

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

How the research was conducted

Da Costa and colleagues used functional magnetic resonance imaging (fMRI) to study how the brain responds to sounds coming from different directions. They compared the brain’s response between six categories of sounds, including positive human vocalizations like erotic sounds, negative vocalizations like a frightened scream, and non-vocalizations like applause, wind, and a ticking bomb. The study included 13 volunteers in their mid-twenties who were all right-handed and had no music training.

Da Costa and colleagues examined brain regions that are crucial for the initial stages of sound processing, including the primary auditory areas A1 and R, the surrounding early-stage auditory areas, and the voice area (VA). These regions are present in both the left and right hemispheres of the brain.

The study found that when participants listened to positive vocalizations from the left, their A1 and R brain regions in both hemispheres were most active. However, when listening to positive vocalizations from the front or right, neutral or negative vocalizations, or non-vocalizations, their A1 and R regions were much less active.

“The strong activation by vocalizations with positive emotional valence coming from the left takes place in the primary auditory cortex of either hemisphere: the first areas in the brain cortex to receive auditory information. Our findings suggest that the nature of a sound, its emotional valence, and its spatial origin are first identified and processed there.”

Furthermore, area L3 in the right hemisphere, but not its counterpart in the left hemisphere, exhibited a greater response to positive vocalizations from the left or right as opposed to those from the front. Conversely, the spatial source of the sound did not affect the response to non-vocalizations.

The evolutionary significance of the brain’s preference for positive vocalizations in the left hemisphere remains unclear.

Senior author Prof Stephanie Clarke, at the Neuropsychology and Neurorehabilitation Clinic at the Lausanne University Hospital said:

Our Sponsors

“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.”