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发帖数: 351 | 1 Formerly Blind Children Shed Light on a Centuries-Old Puzzle
In 1688, an Irish polymath named William Molyneux wrote the English
philosopher John Locke a letter in which he posed a vexing question: Could a
blind person, upon suddenly gaining the ability to see, recognize an object
by sight that he'd previously known by feel? The answer has potentially
important implications for philosophers and neuroscientists alike. Now,
researchers working with a medical charity that provides surgery to restore
vision in blind children say they've found the answer to Molyneux's question
. It's "no" but with a twist.
Molyneux posed his question in the midst of a philosophical debate about how
we comprehend the world around us. An affirmative answer to the question
would support the argument that we possess innate (and presumably God-given)
concepts that are independent of the senses—for example, that we possess a
concept of a sphere, regardless of whether we have only seen one, only felt
one, or both. A negative answer to Molyneux's question would support the
alternative argument that any concept of a sphere or other object must be
tied to sensory experience. In that view, a blind person would have only a
tactile concept of a sphere that would be of no use in recognizing the shape
by sight.
For modern neuroscientists, Molyneux's question raises issues about how the
brain integrates information from the different senses, says Richard Held, a
professor emeritus of brain and cognitive sciences at the Massachusetts
Institute of Technology (MIT) in Cambridge. In search of the elusive answer,
Held teamed up with MIT colleague Pawan Sinha, who founded an organization
in 2003 to help blind children in India. Called Project Prakash, after the
Sanskrit word for "light," the group collaborates with Indian surgeons who
operate to restore sight in children who've been blind from cataracts or
other curable causes.
Held, Sinha, and colleagues recruited five children, ages 8 to 17, from
Project Prakash to tackle Molyneux's question. The researchers built 20
pairs of simple shapes from toy blocks and tested the children within 48
hours of the surgery to restore their sight. The children had not
encountered these unusual shapes before. In one experiment, the researchers
gave the children a shape to feel (without looking), then asked them to feel
two more shapes and indicate which was the same as the first one they'd
felt. All five children chose the right shape more than 90% of the time. In
a second experiment, the children could look but not touch. Again they
nailed it. But on the third and most crucial experiment, their performance
plummeted. After feeling a shape, the children did only slightly better than
chance at identifying it by sight alone, the team reports online today in
Nature Neuroscience.
That result suggests a negative answer to Molyneux's question. Because many
children travel long distances for the operations, most go home with their
families before the researchers can do follow-up experiments, Sinha says.
However, when the researchers retested two of the boys with a new set of
shapes a few days later, their accuracy on the touch-to-vision experiment
jumped to above 80%. That suggests a more nuanced answer of "initially no
but subsequently yes," Sinha says.
"It's a great story," says Alvaro Pascual-Leone, a neurologist and
neuroscientist at Harvard Medical School in Boston. The change in the
children's ability to integrate touch and vision happens too fast to be
explained by major rewiring in the brain, Pascual-Leone says. Even though
they grew up recognizing objects by touch, they needed only a little bit of
visual experience to learn to translate between the two senses. "They're not
starting from zero," he says.
http://dx.doi.org/10.1038/nn.2795 | s*********y
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