Left brain works the crowd at a noisy party

William Atkins
Friday, 16 November 2007 03:18

Science - Biology

Have you ever wondered how you are able to pick out an individual conversation in a room filled with noisy people? Researchers from Germany, Japan, and Canada have found out that the brain’s left hemisphere does more work than the right side in distinguishing  sounds from background noises.     

Basically, the left hemisphere of the brain processes information by using an acoustical technique called “simultaneous masking,” which causes the brain to pick out one sound even though it is surrounded by competing sounds and noises.

Sometimes also called frequency masking, it often occurs when two or more sounds share a frequency band—they are clearly heard when separate, but cannot be heard when together.

The researchers used a neuroimaging technique called magnetoencephalography (MEG) to study the mechanisms of the nerves going on in the brain and, specifically, the differences between this neural activity in the right and left hemispheres of the brain.

The MEG imaging technique measures magnetic fields produced by electrical activity in the brain using highly sensitive devices.

Hidehiko Okamoto, from the Institute for Biomagnetism and Biosignal Analysis (University of Muenster, Germany), and colleagues from Japan and Canada had volunteers listen to different combinations of a primary sound and background noise. The primary sound was played into either the left ear or the right ear, while the background sounds were either introduced into the same ear as was the primary sound or introduced into the other ear.

In all cases, the Okamoto team found that the left hemisphere contained the most neural activity during these times. Thus, it worked harder at picking up sounds even though they were contained in a room filled with loud and competing sounds and noises.

Their research has lead to a better understanding of the neural interactions that are at play in distinguishing various sounds.

The results of their study was presented online November 15, 2007, in the journal BMC Biology. The title of the article is “Left hemispheric dominance during auditory processing in noisy environment.” The other collaborators participating in the study with Okamoto are Henning Stracke, Bernhard Ross, Ryusuke Kakigi and Christo Pantev.