A recent study shows that the mind’s eye can learn to see, even in those who were born blind
By Melissa Healy, Los Angeles Times
People blind from birth can be taught to "see" images that are conveyed as sounds, says a new study that calls into question a longstanding belief about the limits of the human brain.
Devices that scan visual images and reinterpret regularities as sounds were used to retrain the brains of congenitally blind people in a study published this week in the journal Neuron. The authors -- at the Safra Center for Brain Science at Hebrew University in Israel -- put people who had been blind since birth through 70 hours of training with a visual-to-auditory sensory substitution device.
Initially, the subjects were able to distinguish among faces, houses, everyday objects, body shapes and textures. Eventually, they were able to read letters and words, identify facial expressions and locate people's positions. In one video, a blind person is shown a picture of a woman with a ponytail and identified the hairstyle.
Seeing through touch
Blind people have long used the capability to use another sensory perception to compensate for blindness: Braille and blind walking canes allow people without sight to read and navigate. But when the authors of the current study put subjects in a brain scanner, they gained insight into the process by which training with a sensory substitution device allowed the mind's eye to "see."
The human brain is a remarkably efficient and adaptable organ: when an
appendage such as a hand is amputated, or a sensory perception such as
sight is lost, the specialized regions of the brain in which input from
the hand or the eyes is processed are reassigned to other duties.
The amazing brain
But scientists have long believed that the brain's adaptability is
limited by early conditions: when a person is born blind, the capacity
of the brain's visual cortex to process sight never develops, scientists
have believed. With that lost opportunity, a window is closed, and even
if eyesight were to be restored, the visual cortex, they believed,
would forever remain "blind" to images.
Not so, the current study finds. When blind subjects listened to the
"soundscapes" that conveyed information about a visual image, they
showed activation in their visual cortex. In fact, when sounds conveyed
the shape of letters, subjects who had never "seen" a letter showed
activation in a patch of the left ventral visual cortex that uniquely
comes alive when people with normal vision read letters and words.
With the right training approaches and technologies, the brains of
people who have been blind for a long time -- even since birth -- might
be "reawakened" to the task of processing visual information, he said.
For some, he added, such training might even restore some lost vision.
Sight restored
In fact, a 2008 study
first offered tantalizing evidence that scientists were wrong in their
long-held belief that a congenitally blind person could never have
normal vision even if eyesight were restored. A young Indian woman
identified only as SRD was born blind of dense congenital cataracts, but
her vision was restored when she was 12 at the Iladevi Eye Clinic in
Ahmedabad, India. Twenty years after she regained her eyesight, a team
from the Massachusetts Institute of Technology discovered this rare
instance of a congenitally blind person whose vision was restored, and
tested her extensively to see how she saw.
SRD's sight was virtually normal, though the MIT team found that she did
not use certain cognitive tricks that most sighted people use to make
sense of conflicting visual cues.
Vocabulary Focus
call into question (phr v) to cause doubts about something
long-standing adj. having existed for a long time
auditory adj. of or involving hearing
sensory adj. of or related to the physical senses of touch, smell, taste, sight and hearing
appendage n. a smaller or less important part hat is attached to something
activation n. a moment when something starts working
extensively adv. widely, broadly, with great detail
congenital adj. 天生的, 先天的
describes a disease or condition that exists at or from birth
Braille n. 盲人點字法
a system of printing for blind people in which each letter is represented as a raised pattern that can be ready by touching it with the fingers
visual cortex n. 視覺皮質
the part of the brain that helps deal with what the eyes see
cataract n. 白內障
an area of the eye that changes to become unclear, causing a person not to see well, or this condition of the eye
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