Differences in brain usage among Braille readers
shed new light on the relationship between thought and
language
By David F. Salisbury
November 30, 2001
Individuals who have been blind from birth use different parts of their brain when reading
Braille than those who lost their sight early in life … a difference that sheds new light on the
relationship between thought and language.
That is the conclusion of a study performed by Vanderbilt researchers and reported in the
November issue of the scientific journal Human Brain Mapping. The research is one of the latest
efforts to understand the structure of the human brain and how it responds to injury.
Twenty years ago most neuroscientists thought that the adult human brain had a very
limited ability to reorganize itself following major injuries to the brain itself or to the peripheral
nervous system that provides it with sensory information. In recent years, however, researchers
have discovered that mature brains, as well as developing brains, display more flexibility than
they had thought.
One way to study the phenomena associated with brain plasticity is to examine
differences in brain organization in people who have lost their sight at an early age. In sighted
individuals, nearly one third of the brain is devoted to processing visual information. Cutting off all
sensory input to such a large region of the cortex creates a situation where recruitment of some
of the unused areas by the other senses seems likely. So scientists have looked for, and found,
evidence that some of the areas of the idle visual cortex can be recruited to process other types
of sensory information.
In 1996 a Japanese scientist, N. Sadato, working at the National Institutes of Health,
reported that positron emission tomography (PET) scans averaged from the brains of several
blind subjects displayed activity in parts of the visual cortex while reading Braille. It was unclear,
however, to what extend this activity might represent activation of visual memories that
individuals had acquired before they were blind and how much represented an actual repurposing
of visual areas of the brain to handle touch information.
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Differences in brain usage among Braille readers shed new light on the
relationship between thought and language
To help answer this question, Psychology Professor Ford F. Ebner and Research
Assistant Professor of Psychology Peter Melzer – with technical assistance from members of
Vanderbilt’s radiology department – turned to functional Magnetic Resonance Imaging (fMRI), a
technique can detect active areas of brain activity by measuring activity-induced changes in blood
flow.
In order to distinguish between activation of visual memories and processing of touch
information, the investigators recruited a group of five men and five women, half of whom had
been blind since birth and half of whom lost their sight early in life. The researchers reasoned that
those who had been blind since birth would not have had an opportunity to store up visual
memories, so all the brain activity that they exhibited in areas associated with the visual system
would be areas that had been recruited to process sensory touch information.
The subjects were asked to read a series of single words in Braille. Ten percent of the
words were nouns that referred to abstract concepts while 90 percent were nouns that referred to
objects associated with visual images.
FMRI takes snapshots of brain activity much more quickly than PET scans, which must
average brain activity over several minutes and pool the data from several individuals. By asking
their subjects to alternate reading and resting, the researchers were not only able to measure
which areas become active but also when the activation occurred relative to the initial stimuli.
This allowed them to differentiate between areas involved in the response to the touch
information and those that were not activated by act of reading but by some type of higher-level
processing.
Surprisingly, the researchers did not find major differences in the magnitude and expanse
of activation in the visual cortex between the two groups. But they did find striking differences in
the activation behavior, the relationship between the timing of the activation of specific visual
areas and the task. In the blind-from-birth group, activation of a region in the posterior temporal
lobe that is involved in phonological word processing – keeping track of the sound patterns and
rules of pronunciation in speech – was more strongly correlated with reading than it was in the
group with some visual experience. Conversely, an adjacent region associated with semantic
word processing – determining the meaning of similarly sounding words like flour and flower –
had the stronger correlation with the task in the group with some visual experience than it did in
the group that was blind from birth.
The researchers hypothesize that even a short period of early visual experience may
make it harder to recruit certain areas in the visual cortex than is the case for those who are blind
for birth. They propose that this may be one reason why those who are blind from birth tend to be
much better Braille readers than those who loose their sight later in life, they say.
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Differences in brain usage among Braille readers shed new light on the
relationship between thought and language
The study also provides new support for the proposition that a kind of mental imagery
exists which is independent of the five senses. The subjects who were blind from birth reported
having non-visual associations with some of the words. The areas of the brain that are involved in
high-level processing of the words in the study strongly suggest that this non-visual imagery is
closely related to language. So there is a good chance that further studies may shed new light on
an outstanding issue in philosophy and psychology: the relationship between language and
thought.
Also contributing to the study were Assistant Professor Victoria L. Morgan, Associate
Professor David R. Pickens and Professor Ronald R. Price from the department of radiology and
radiological services, and Robert S. Wall, assistant professor of hearing and speech at
Vanderbilt’s Bill Wilkerson Center.
Funding was provided by the National Institute of Neurological Disorders and Stroke, the
John F. Kennedy Center for Research in Human Development at Vanderbilt University, the
Vanderbilt Vision Research Center, the Hobbs Foundation and Dr. and Mrs. Irwin Eskind.
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