Being blind isn’t just a matter of living in total darkness. There are levels of blindness, from being legally blind, which is having vision that is 20/200 or less, to complete blindness whereby a person cannot make out shadows or light. Still, no matter what level of blindness a person has, it’s not like he or she is just sitting around and listening to the radio or audiobooks. Their brains are adapting so that they can function. Recent research at the University of Washington and Johns Hopkins University has shown that the brain of a blind person is working hard so that they can adapt and function in everyday life.
Work done at the University of Washington demonstrated two differences in the brain of a blind person that may be responsible for their increased ability to make use of auditory information. While it has been known that persons who are born blind have a heighten sense of hearing, it had not been known how this develops in their brains.
Scientists used functional MRI tests to explore what happens in the brains of a blind person as they are listening to sounds. They just weren’t looking at which parts of the brains were active. They also wanted to learn about how the brain processes differences in the frequency of sound.
“We weren’t measuring how rapidly neurons fire, but rather how accurately populations of neurons represent information about sound,” said Kelly Chang, a graduate student in the University of Washington Department of Psychology.
Scientists found that the part of the brain responsible for processing hearing, the auditory cortex, showed narrower neural tuning when it came to distinguishing subtle differences in sound frequency. This showed that blindness leads to increased flexibility in the auditory cortex proving the brain develops an enhanced ability to detect sounds for a blind person over a sighted person.
Another study, this one at Johns Hopkins University, wanted to see how blind persons perceive color. The 17th century English philosopher John Locke stated that people who are born blind cannot truly understand color. They would know intellectually that bananas are yellow, but not know what the color yellow is. Scientists wanted to learn how true this is.
A two-phase experiment was done with blind and sighted adults. They were asked about the color of objects, why they were that color and the likelihood two of those items chosen at random would be the same color. The items were a combination of natural things, such as fruits or plants, and manufactured items, such as a pen or a stop sign.
While the blind test subjects didn’t always agree with sighted test subjects about arbitrary color facts, such as bananas being yellow, the blind subjects’ judgement about how likely two bananas will be the same color was the same as sighted subjects. This result was the same for different types of objects, such as stop signs. Subjects also displayed the same depth of understanding in explaining why objects had certain colors. Although their determination of what color an item is often differed. For example, sighted subjects said that polar bears are white to blend in with the surroundings, whereas many blind subjects said that polar bears are black to absorb heat and stay warm.
Researchers then asked subjects to make predictions about the colors of objects they had never seen in an “explorer on an island” scenario. They told the subjects about items on a remote island that included a “green gem that is spiky and the size of a hand” and a triangular yellow object that is the size of a thumb. Both blind and sighted subjects made the same judgments about these objects, showing that the knowledge of color relates to new examples and doesn’t depend on memorization.