Science

Blind children's brains rewire themselves to track moving objects by boosting their sense of sound


Changes in the brain activity of a blind person from a young age could really give them superior powers to detect sound, scientists have found.

The latest finding could lend some scientific basis to the superhuman abilities of Marvel superhero Daredevil, who was blinded from childhood but fights crime using his other enhanced senses.

Experts found that differences in the part of the brain known as the auditory cortex let blind people register tonal frequencies more precisely than the average person. 

Activity in another section of the brain normally used to track movements visually was also boosted in response to the travel of sound.

That suggests that blind people are able to use sound to navigate the environment around them more effectively.

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Differences in two areas of the brain give a blind person superior ability to detect sound frequencies and track moving sound, a new study has found. This picture shows the Marvel superhero Daredevil, who is blind but has unusually heightened senses that let him 'see'

Differences in two areas of the brain give a blind person superior ability to detect sound frequencies and track moving sound, a new study has found. This picture shows the Marvel superhero Daredevil, who is blind but has unusually heightened senses that let him ‘see’

Two new studies from the University of Washington, one in conjunction with the University of Cambridge, has shown that the brains of blind people were more sensitive to different frequencies as well as their movement through space.  

Researchers looking at brain activity in responses to different sound frequencies showed that blind individuals more accurately identified frequencies, and had better spacial awareness of it.  

In the first study, they used MRI scanning machine to record brain activities of participants while they listened to a sequence of codes similar to the Morse code that has tones of different frequencies.  

Kelly Chang, a graduate student in the UW Department of Psychology and author on both papers in the Journal of Neuroscience paper said:  ‘Our study shows that the brains of blind individuals are better able to represent frequencies.’ 

The researchers called this a ‘more refined frequency tuning’ in the audio ability of blind participants.

The study was one of the first to investigate effects of early blindness on auditory cortex, and found the auditory cortex more accurately represented the frequency of each sound than in individuals with sight.       

This was true for individuals who became blind early in life or whose eyes failed to develop at all.  

Changes to the part of the brain known as the auditory cortex, responsible for picking up sound allowed blind individuals to register tonal frequencies more accurately than the average person gives some basis to the heightened senses of the blind Marvel superhero Daredevil

Changes to the part of the brain known as the auditory cortex, responsible for picking up sound allowed blind individuals to register tonal frequencies more accurately than the average person gives some basis to the heightened senses of the blind Marvel superhero Daredevil

Ms Chang said: ‘For a sighted person, having an accurate representation of sound isn’t as important because they have sight to help them recognise objects, while blind individuals only have auditory information.

‘This gives us an idea of what changes in the brain explain why blind people are better at picking out and identifying sounds in the environment.  

‘This is the first study to show that blindness results in plasticity in the auditory cortex. 

‘In blind individuals, more information needs to be extracted from sound — and this region seems to develop enhanced capacities as a result.’ 

In the second study, the participants once again listened to tones of different frequency, but the sounds seemed to be moving rather than static. 

The researchers found those who were ‘early blind’ individuals showed more activity in an area of the brain called the human motion complex or hMT+ which is normally responsible for tracking objects visually in sighted individuals.  

In blind subjects, the researchers found that it was still responsible for movement tracking, but through sound.  

Researchers measured responses to sound frequency in the auditory cortex - the brain areas in red (left) showed the greatest response to low-pitched tones while the blue showed response to high pitched tones. Blind subjects were better at identifying sounds by tonal frequencies

Researchers measured responses to sound frequency in the auditory cortex – the brain areas in red (left) showed the greatest response to low-pitched tones while the blue showed response to high pitched tones. Blind subjects were better at identifying sounds by tonal frequencies

The responses in the the auditory cortex showed differences in activity for sighted individuals (left) and those who were blinded from childhood (A-B) compared to those who had their sight restored as adults (C-D)

The responses in the the auditory cortex showed differences in activity for sighted individuals (left) and those who were blinded from childhood (A-B) compared to those who had their sight restored as adults (C-D)

Dr Ione Fine, from the University of Washington who was an author on both studies, said: ‘These results suggest that early blindness results in visual areas being recruited to solve auditory tasks in a relatively sophisticated way. 

It suggests that blind individuals uses or ‘recruits’ this area of the brain that is used for visual tracking in order to track objects by their sound frequency.

‘In blind individuals the neural responses in area hMT+ contained information about the direction of motion of the sounds, whereas in the sighted participants these sounds did not produce significant neural activity.’

In participants who had been blind from infancy until adulthood but then had sight restored via surgery as an adult, the hMT+ seemed to serve a dual purpose, capable of processing both auditory and visual motion. 

Further research in these individuals, including their vision as adults could reveal the mechanisms behind these changes, say researchers.



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