14 DAY TRIAL // The left cortical hemisphere realizes this through an acoustical technique named "simultaneous masking", which enables the brain to distinguish one sound even when it comes together with competing sounds and noises. Also named frequency masking, the process often takes place when two or more sounds with a similar frequency, which are clearly heard in separate situations, cannot merge when emitted together, confusing the listener.
The team employed magnetoencephalography (MEG), a neuroimaging technology to investigate the differences between the brain's right and left hemisphere's activity by assessing magnetic fields triggered by the brain's electrical activity.
The team led by Hidehiko Okamoto, from the Institute for Biomagnetism and Biosignal Analysis (University of Muenster, Germany), required the subjects to listen to various combinations of a primary sound and background noise. The listeners heard the primary sound either into the left ear or the right ear, while the background sounds were heard either into the same ear as the primary sound or into the other ear.
The left hemisphere was the most active in all trials. It managed to distinguish between sounds even when the subjects were exposed to the environment of a party room filled with loud and competing sounds.
These results, even if a novelty, should not be a surprise, as the complex human speech has been linked to two brain nuclei controlling the language (articulating control, data storing and integration of the grammar rules) located in the left hemisphere of the cortex. What we want to say starts in an area of the left cortex called "Wernicke zone". This connects with "Broca zone", involved with grammatical rules. Impulses go from these areas to the muscles involved in speech. These areas are connected with the visual system (so we can read), auditory system (so we can hear what others say, understand and answer) and also have a memory bank for recalling valuable phrases.