Researchers have long wondered why blind people seem to have a sharpened sense of hearing. Now a Seattle team has pinpointed specific brain adaptations that occur in people without sight.
"There's this idea that blind people are good at auditory tasks, because they have to make their way in the world without visual information. We wanted to explore how this happens in the brain," said Ione Fine, a psychology professor at the University of Washington (UW).
More information about sound
Fine is the senior author of a pair of studies in which researchers used functional MRI to detect two specific hearing-related changes in blind people's brains.
Rather than identifying which parts of the brain are most active while listening, the researchers examined the sensitivity of the brain to slight differences in auditory frequency.
One study was published this week in the Journal of Neuroscience and the other in the Proceedings of the National Academy of Sciences.
According to Kelly Chang, the lead author of the Journal of Neuroscience study, the researchers "weren't measuring how rapidly neurons fire, but rather how accurately populations of neurons represent information about sound." Chang is a graduate student in the UW psychology department.
The investigators found that compared to a sighted person, a blind person's auditory cortex was better able to detect small differences in sound frequency.
Using sound to track moving objects
Fine said, "This is the first study to show that blindness results in plasticity in the auditory cortex. This is important because this is an area of the brain that receives very similar auditory information in blind and sighted individuals. But in blind individuals, more information needs to be extracted from sound – and this region seems to develop enhanced capacities as a result."
The other study examined how the brains of people who are born blind or go blind early in life use sound to track moving objects.
The researchers came to focus on an area of the brain called the hMT+, which in sighted people is responsible for tracking moving objects they see. In sightless people, it tracks the sounds of moving objects, such as cars or footsteps, the study authors said.
"These results suggest that early blindness results in visual areas being recruited to solve auditory tasks in a relatively sophisticated way," Fine said in a university news release.
According to Chang, the research showed "that the brains of blind individuals are better able to represent frequencies".
In addition, the findings provide "an idea of what changes in the brain explain why blind people are better at picking out and identifying sounds in the environment".
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