Researchers turn current sound-localization theories 'on their ear'

December 3, 2013
ear

The ability to localize the source of sound is important for navigating the world and for listening in noisy environments like restaurants, an action that is particularly difficult for elderly or hearing impaired people. Having two ears allows animals to localize the source of a sound. For example, barn owls can snatch their prey in complete darkness by relying on sound alone. It has been known for a long time that this ability depends on tiny differences in the sounds that arrive at each ear, including differences in the time of arrival: in humans, for example, sound will arrive at the ear closer to the source up to half a millisecond earlier than it arrives at the other ear. These differences are called interaural time differences. However, the way that the brain processes this information to figure out where the sound came from has been the source of much debate.

A recent paper by Mass. Eye and Ear/Harvard Medical School researchers in collaboration with researchers at the Ecole Normale Superieure, France, challenge the two dominant theories of how people localize sounds, explain why neuronal responses to sounds are so diverse and show how sound can be localized, even with the absence of one half of the . Their research is described on line in the journal eLife.

"Progress has been made in laboratory settings to understand how sound localization works, but in the real world people hear a wide range of sounds with background noise and reflections," said Dan F. M. Goodman, lead author and post-doctoral fellow in the Eaton-Peabody Laboratories at Mass. Eye and Ear, Harvard Medical School. "Theories based on more realistic environments are important. The theme of the paper is that previous theories about this have been too idealized, and if you use more realistic data, you come to an entirely different conclusion."

"Two theories have come to dominate our understanding of how the brain localizes sounds: the peak coding theory (which says that only the most strongly responding brain cells are needed), and the hemispheric coding theory (which says that only the average response of the cells in the two hemispheres of the brain are needed)," Goodman said. "What we've shown in this study is that neither of these theories can be right, and that the evidence they presented only works because their experiments used unnatural/idealized sounds. If you use more realistic, natural sounds, then they both do very badly at explaining the data."

Researchers showed that to do well with realistic sounds, one needs to use the whole pattern of neural responses, not just the most strongly responding or average response. They showed two other key things: first, it has long been known that the responses of different auditory neurons are very diverse, but this diversity was not used in the hemispheric coding theory.

"We showed that the diversity is essential to the brain's ability to localize sounds; if you make all the responses similar then there isn't enough information, something that was not appreciated before because if one has unnatural/idealized sounds you don't see the difference" Goodman said.

Second, previous theories are inconsistent with the well-known fact that people are still able to localize sounds if they lose one half of our brain, but only sounds on the other side (i.e. if one loses the left half of the brain, he or she can still localize sounds coming from the right), he added.

"We can explain why this is the case with our new theory," Goodman said.

Explore further: Decoding sound's source: Researchers unravel part of the mystery

Related Stories

Decoding sound's source: Researchers unravel part of the mystery

October 1, 2013
As Baby Boomers age, many experience difficulty in hearing and understanding conversations in noisy environments such as restaurants. People who are hearing-impaired and who wear hearing aids or cochlear implants are even ...

Brain picks out salient sounds from background noise by tracking frequency and time

July 23, 2013
New research reveals how our brains are able to pick out important sounds from the noisy world around us. The findings, published online today in the journal 'eLife', could lead to new diagnostic tests for hearing disorders.

Insights into how brain compensates for recurring hearing loss point to new glue ear therapies

June 27, 2013
Important new insights into how the brain compensates for temporary hearing loss during infancy, such as that commonly experienced by children with glue ear, are revealed in a research study in ferrets. The Wellcome Trust-funded ...

Why we look at the puppet, not the ventriloquist

August 30, 2013
(Medical Xpress)—As ventriloquists have long known, your eyes can sometimes tell your brain where a sound is coming from more convincingly than your ears can.

Feedback loops and localization errors

October 24, 2013
Neurobiologists at Ludwig Maximilian University of Munich describe a feedback loop that modulates the processing of auditory signals in the brainstem in a frequency-dependent manner, and can lead to systematic errors in the ...

Study finds potential key to learning a new language

November 20, 2013
A new study by University of Houston (UH) researchers may lead to dramatic changes in the way language is taught and learned – especially a second language. These findings are important because statistics show 60 percent ...

Recommended for you

Hibernating ground squirrels provide clues to new stroke treatments

November 17, 2017
In the fight against brain damage caused by stroke, researchers have turned to an unlikely source of inspiration: hibernating ground squirrels.

Age and gut bacteria contribute to multiple sclerosis disease progression

November 17, 2017
Researchers at Rutgers Robert Wood Johnson Medical School published a study suggesting that gut bacteria at young age can contribute to multiple sclerosis (MS) disease onset and progression.

Molecular guardian defends cells, organs against excess cholesterol

November 16, 2017
A team of researchers at the Harvard T. H. Chan School of Public Health has illuminated a critical player in cholesterol metabolism that acts as a molecular guardian in cells to help maintain cholesterol levels within a safe, ...

Prototype ear plug sensor could improve monitoring of vital signs

November 16, 2017
Scientists have developed a sensor that fits in the ear, with the aim of monitoring the heart, brain and lungs functions for health and fitness.

Ancient enzyme could boost power of liquid biopsies to detect and profile cancers

November 16, 2017
Scientists are developing a set of medical tests called liquid biopsies that can rapidly detect the presence of cancers, infectious diseases and other conditions from only a small blood sample. Researchers at The University ...

FDA to crack down on risky stem cell offerings

November 16, 2017
U.S. health authorities announced plans Thursday to crack down on doctors pushing stem cell procedures that pose the gravest risks to patients amid an effort to police a burgeoning medical field that previously has received ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.