New research overturns old ideas about how hearing works

The way humans experience music and language is different
from what was previously thought.
This is the finding
of a study conducted by researchers at Oregon Health and Science University in Sweden and the United States.
The findings, recently published in the journal Science Advances, could improve cochlear implant design
.

We are social animals
.
We value listening to other people's voices, and we use our hearing to recognize and experience human language and sounds
.
Sound entering the outer ear travels through the eardrum to the spiral inner ear, also known as the cochlea
.
The cochlea is home to outer and inner hair cells, which are sensory cells
for hearing.
The "hair" of the internal hair cells is bent by sound waves, and signals are transmitted through nerves to the brain, which interprets the sounds
we hear.

For the past 100 years, we have believed that each sensory cell has its own "optimal frequency" (a measure of the number of sound waves per second).

This frequency causes the strongest response
from hair cells.
This means that sensory cells with an optimal frequency of 1000 Hz respond significantly less
to sounds with slightly lower or higher frequencies.
It is also thought that the various parts of the cochlea function similarly
.
However, a team of researchers found that this was not the
case for sensory cells that processed low-frequency sounds with frequencies below 1,000 hertz.
Vowels in human language fall into this category
.

"Our study shows that many cells in the inner ear respond
simultaneously to low-frequency sounds.
Anders Fridberger, a professor in the Department of Biomedical and Clinical Sciences, said: "We think this makes it easier for people to experience low-frequency sounds because the brain receives information
from many sensory cells at the same time.
"

Scientists believe that this structure of our hearing system makes it
stronger.
If some sensory cells are damaged, many of the remaining cells can send nerve impulses
to the brain.

It's not just vowels in human language that are located in the low-frequency region: many of the sounds that make up music are also located in this region
.
For example, the frequency of alto C on a piano is 262 Hz
.

These results may eventually be important
for people with severe hearing impairment.
The most successful treatment in this situation is cochlear implantation, in which electrodes are implanted into the cochlea
.

"The current design of cochlear implants is based on the assumption that each electrode can only stimulate nerves at specific frequencies, in a way
that tries to replicate the function of our hearing system.
We recommend changing the stimulation method at low frequencies to bring it closer to natural stimulation, and the user's hearing experience should be improved in this way," Fridberger said
.

The researchers now plan to study how to apply their new knowledge into practice
.
One project they are working on involves a new way
to stimulate the low-frequency part of the cochlea.

The results come from experiments with guinea pig cochlea, which hear similarly
to humans in low-frequency regions.

References:

Best frequencies and temporal delays are similar across the low-frequency regions of the guinea pig cochlea” by George Burwood, Pierre Hakizimana, Alfred L Nuttall and Anders Fridberger, 23 September 2022, Science Advances.