By: Tharuneeka Jeevarajan
Two ears, but why not two sounds? “While this helps us determine which direction sounds are coming from, it also means that our brain has to combine the information from both ears. Otherwise, we would hear an echo,” stated Basil Preisig of the Department of Psychology at the University of Zurich.
Sound that is heard in the right ear reaches the left brain hemispheres first, on the contrary, sound that is heard in the left ear reaches the right brain hemisphere first. Correspondingly, each hemisphere has its own tasks when processing speech. The left hemisphere identifies the different phonemes and syllables. The right hemisphere identifies prosody and rhythm in speech. But, despite the differences, the brain translates what is heard into one sound that humans understand.
Ideally, to prove the process of processing sound was studied and further understood. Past studies outline that Basil Preisig identifies the role of gamma waves in processing sound. It was concluded that the syncing of the gamma waves is related to the process of unifying what we hear.
Neurolinguists, who study the brain when processing language related information in the physiological aspect, from UZH worked on a study to get a deeper understanding. The study at Donders Center for Cognitive Neuroimaging in Nijmegen, the Netherlands revolved around 28 subjects, who were instructed to complete the listening tasks. During the task, where the speech sound, ga and da, was played ambiguously in the right ear while fragments of the syllables ga or da were played unknowingly in the left ear, the subjects were expected to report what they hear, while the researchers monitored the brain hemispheres using functional magnetic resonance imaging (fMRI).
Magnetic resonance imaging (MRI), is a non-invasive test that uses magnetic fields and radio waves to produce a computerized image of the internal body. With this it is easy to examine and diagnose for medical professionals. fMRI uses the same imaging as MRI to measure the changes in blood flow in active parts of the brain.
During the study, when changing the natural activity of gamma waves by using electrodes that simulates both brain hemispheres, it resulted in the participants’ lack of ability to correctly identify the syllables. fMRI shows changes in the neural connections between both hemispheres. The connection strength changed based on the electrode influenced rhythm of the gamma waves synchronously or asynchronously. Concluding with the results of disruption in the unifying process of what one hears.
"Our results suggest that gamma wave-mediated synchronization between different brain areas is a fundamental mechanism for neural integration," says Preisig.
References:
University of Zurich. "Synchronization of brain hemispheres changes what we hear." ScienceDaily. ScienceDaily, 8 February 2021. <www.sciencedaily.com/releases/2021/02/210208173103.htm>.
(ACR), R., 2018. Magnetic Resonance, Functional (fMRI) - Brain. [online] Radiologyinfo.org. Available at: <https://www.radiologyinfo.org/en/info.cfm?pg=fmribrain#:~:text=Magnetic%20resonance%20imaging%20(MRI)%20is,radiation%20(x%2Drays).>.
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