Found the Reason Why Congenitally Visually Impaired Have Exceptional Auditory Abilities

Nowon Eulji University Hospital Professor Shim Hyun-jun's Team
Comparative Analysis of Central Auditory Processing Ability
Confirmed Improvement in 'Right Cerebral Hemisphere' Function Responsible for Sound Pattern and Timbre Recognition
"Important Role in Rehabilitation of Hearing Loss in Visually Impaired"

Professor Shim Hyun-jun, Department of Otorhinolaryngology, Nowon Eulji University Hospital.

[Asia Economy Reporter Lee Gwan-joo] The reason why congenitally visually impaired individuals have superior auditory abilities compared to those without visual impairments has been identified for the first time by domestic researchers.

Professor Shim Hyun-jun's team from the Department of Otorhinolaryngology at Nowon Eulji University Hospital announced on the 29th that, based on a comparative analysis of central auditory processing abilities between congenitally visually impaired and non-visually impaired individuals, they confirmed enhanced function of the right cerebral hemisphere, which recognizes sound patterns and timbre, in visually impaired individuals.

The human brain is divided into left and right hemispheres based on a central long groove. All nerve bundles in the body pass through the pons and head toward the opposite hemisphere. Therefore, sounds entering the left and right ears are transmitted to the opposite side of the brain.

Professor Shim's team found that in congenitally visually impaired individuals, the function of the right cerebral hemisphere, which recognizes sound patterns and timbre, is more enhanced than that of the left cerebral hemisphere, which is responsible for understanding language. This is because the brain becomes sensitively responsive to auditory stimuli and develops compensatorily due to long-term deprivation of visual information.

Specifically, Professor Shim's team conducted comparative analyses of central auditory processing abilities through dichotic listening tests, frequency pattern tests, and speech recognition tests in noisy environments on 23 congenitally visually impaired individuals and 22 non-visually impaired individuals.

The 'dichotic listening test,' which assesses recognition ability when different sounds enter both ears, involves simultaneously presenting three different numbers and identifying which sounds were heard. In this test, non-visually impaired individuals showed right ear dominance with scores of 15 for the right ear and 12 for the left ear, indicating better recognition of sounds heard through the right ear. In contrast, visually impaired individuals scored 15 for the right ear and 16 for the left ear, showing significantly better performance in the left ear compared to non-visually impaired individuals. This suggests that the function of the right cerebral hemisphere connected to the left ear is more developed in visually impaired individuals.

The 'frequency pattern test' involves randomly combining five sounds of high and low frequencies to match the sound pattern. This test measures the function of the right cerebral hemisphere, which recognizes sound patterns and timbre, through responses that follow the pitch. Visually impaired individuals scored 15 for both ears, while non-visually impaired individuals scored 13 and 14 for the left and right ears, respectively. The superior performance of visually impaired individuals in both ears confirms the relative development of the right cerebral hemisphere.

Additionally, in the 'speech recognition in noise' test, which was conducted by dividing noise levels into five stages, visually impaired individuals showed superior performance only at the highest noise level of -8 dB compared to non-visually impaired individuals. In EEG tests, visually impaired individuals exhibited stronger brainwave responses than non-visually impaired individuals at noise levels of -8 dB and -4 dB. The lack of difference in speech recognition between visually impaired and non-visually impaired individuals under low noise conditions is interpreted as the left cerebral hemisphere, responsible for language and text comprehension, showing no significant difference between the two groups.

Professor Shim explained, "This study revealed a new fact that long-term visual loss develops the function of the right brain hemisphere," adding, "It will play an important role in providing differentiated auditory rehabilitation when hearing loss occurs in visually impaired individuals in the future."

This study was published in the May issue of 'Frontiers in Psychology,' a SCIE-level neuroscience journal.