The Part of the Brain that Processes Visual Text May Not Require Vision After All
by Maureen Duffy
I first published this story last year, but believe it's equally relevant today. I think you'll agree.
Congenital Blindness, the Visual Cortex, and Language Processing
Two intriguing research reports are shedding new light on the way the brain's visual processing center functions in people who are blind.
The first report, published in the Proceedings of the National Academy of Sciences, entitled Language processing in the occipital cortex of congenitally blind adults, examines how "…brain regions that are thought to have evolved for vision can take on language processing as a result of early experience," according to lead author Marina Bedny, Ph.D., from the Massachusetts Institute of Technology (MIT) and Harvard Medical School:
Humans are thought to have evolved brain regions in the left frontal and temporal cortex that are uniquely capable of language processing. However, congenitally blind individuals also activate the visual cortex in some verbal tasks. We provide evidence that this visual cortex activity in fact reflects language processing. We find that in congenitally blind individuals, the left visual cortex behaves similarly to classic language regions.
According to the authors, studies in the past have shown that people who have been blind since birth also use the visual cortex during verbal tasks such as reading braille, and have good verbal long-term memory. It was unclear, however, if the visual cortex processed complex language, such as sentences, in the same way as in the classic language regions in the brain.
The researchers found that the left visual cortex of the blind study participants (22 people who were blind from birth and 39 sighted people) was active during sentence comprehension. This could indicate that "... experience can have a really a big impact on the function of a piece of brain tissue," said Dr. Bedny. "It suggests that a part of the brain can participate in language processing without having evolved to do so."
Braille Reading and the Brain's Visual Word Form Area
The second study, published in Current Biology, entitled A Ventral Visual Stream Reading Center Independent of Visual Experience, examines the brain's visual word form area (VWFA), a section of the brain that develops expertise for visual reading:
The visual word form area (VWFA) ... is activated across writing systems and scripts and encodes strings of letters irrespective of case, font, or location in the visual field. In the blind, comparable reading expertise can be achieved using braille. This study investigated which area plays the role of the VWFA in the blind.
Using functional magnetic resonance imaging (MRI), we show that activation during braille reading in [eight congenitally] blind individuals peaks in the VWFA, with striking ... consistency within and between blind and sighted subjects.
Thus, we propose that the VWFA is a [multisensory] reading area that develops specialization for reading regardless of visual experience.
In an interview with the New York Times, Amir Amedi, Ph.D., a neuroscientist from the Hebrew University of Jerusalem and one of the study authors, summarized the implications of their research:
'It doesn't matter if people are reading with their eyes or by their hands,' said Dr. Amedi. 'They are processing words. What we suggest is that what this area is doing is building the shape of the words, even though we call it the visual word form area.'
He and his colleagues belong to a small community of neuroscientists who are trying to demonstrate that the brain's regions are multisensory. Although the theory has not become mainstream, it has been gaining acceptance in the past decade.
'We hope that this paper will be another break in convincing people,' Dr. Amedi said. 'But one or two or 10 papers is not enough to change the textbook. It might take another decade, so we can prove that we haven't missed something.'
Exciting research, wouldn't you say? VisionAware will provide updates of relevant brain research as they become available.
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