Tuesday, December 8, 2009

Your Brain on Books

Your Brain on Books: Neuroscientist Stanislas Dehaene explains his quest to
understand how the mind makes sense of written language

By Stanislas Dehaene, Scientific American, November 17, 2009

Stanislas Dehaene holds the chair of Experimental Cognitive Psychology at
the Collège de France, and he is also the director of the INSERM-CEA
Cognitive Neuroimaging Unit (http://www.unicog.org) at NeuroSpin, France's
most advanced neuroimaging research center. He is best known for his
research into the brain basis of numbers, popularized in his book, "The
Number Sense." In his new book, "Reading in the Brain," he describes his
quest to understand an astounding feat that most of us take for granted:
translating marks on a page (or a screen) into language. He answered
questions recently from Mind Matters editor Gareth Cook.

COOK: How did you become interested in the neuroscience of reading?

DEHAENE: One of my long-time interests concerns how the human brain is
changed by education and culture. Learning to read seems to be one of the
more important changes that we impose to our children's brain. The impact
that it has on us is tantalizing. It raises very fundamental issues of how
the brain and culture interact.

As I started to do experimental research in this domain, using the different
tools at my disposal (from behavior to patients, fMRI, event-related
potentials, and even intracranial electrodes), I was struck that we always
found the same areas involved in the reading process. I began to wonder how
it was even possible that our brain could adapt to reading, given it
obviously never evolved for that purpose. The search for an answer resulted
in this book. And, in the end, reading forces us to propose a very different
view of the relationship between culture and the brain.

COOK: What is this "new relationship"?

DEHAENE: A classical, although often implicit, view in social science is
that the human brain, unlike that of other animals, is a learning machine
which can adapt to essentially any novel cultural task, however complex. We
humans would be liberated from our past instincts and free to invent
entirely new cultural forms.

What I am proposing is that the human brain is a much more constrained organ
than we think, and that it places strong limits on the range of possible
cultural forms. Essentially, the brain did not evolve for culture, but
culture evolved to be learnable by the brain. Through its cultural
inventions, humanity constantly searched for specific niches in the brain,
wherever there is a space of plasticity that can be exploited to "recycle" a
brain area and put it to a novel use. Reading, mathematics, tool use, music,
religious systems -- all might be viewed as instances of cortical recycling.

Of course, this view of culture as a constrained "lego" game isn't that
novel. It is deeply related to the structuralist view of anthropology, as
exemplified by Claude Levi-Strauss and Dan Sperber. What I am proposing is
that the universal structures that recur across cultures are, in fact,
ultimately traceable to specific brain systems.

In the case of reading, the shapes of our writing systems have evolved
towards a progressive simplification while remaining compatible with the
visual coding scheme that is present in all primate brains. A fascinating
discovery, made by the American researcher Marc Changizi, is that all of the
world's writing systems use the same set of basic shapes, and that these
shapes are already a part of the visual system in all primates, because they
are also useful for coding natural visual scenes. The monkey brain already
contains neurons that preferentially respond to an "alphabet" of shapes
including T, L, Y. We merely "recycle" these shapes (and the corresponding
part of cortex) and turn them into a cultural code for language.

COOK: In the book, you describe a part of the brain as the "letterbox." Can
you please explain what you mean by that?

DEHAENE: This is the name I have given to a brain region that systematically
responds whenever we read words. It is in the left hemisphere, on the
inferior face, and belongs to the visual region that helps us recognize our
environment. This particular region specializes in written characters and
words. What is fascinating is that it is at the same location in all of us -
whether we read Chinese, Hebrew or English, whether we've learned with
whole-language or phonics methods, a single brain region seems to take on
the function of recognizing the visual word.

COOK: But reading is a relatively recent invention, so what was the
"letterbox" doing before we had written language?

DEHAENE: An excellent question - we don't really know. The whole region in
which this area is inserted is involved in invariant visual recognition - it
helps us recognize objects, faces and scenes, regardless of the particular
viewpoint, lighting, and other superficial variations.

We are starting to do brain-imaging experiments in illiterates, and we find
that this region, before it responds to words, has a preference for pictures
of objects and faces. We are also finding that this region is especially
attuned to small features present in the contours of natural shapes, such as
the "Y" shape in the branches of trees. My hypothesis is our letters emerged
from a recycling of those shapes at the cultural level.

The brain didn't have enough time to evolve "for" reading - so writing
systems evolved "for" the brain!

COOK: How might our brains abilities, and limits, shape other human
activities, like, say mathematics?

DEHAENE: I dedicated a whole book, "The Number Sense," to our native
intuitions of numbers and how they shape our mathematics. Basically, we
inherit from our evolution only a rudimentary sense of number. We share it
with other animals, and even infants possess it already in the first few
months of life. However, it is only approximate and non-symbolic - it does
not allow us to precisely distinguish 13 from 14 objects.

Nevertheless, it gave humanity the concept of number, and we then learned to
extend it with cultural symbols such as digits and count words, thus
achieving a more precise way of doing arithmetic.

We can still find traces of this evolutionarily old system whenever we
approximate, sometimes quite irrationally - for instance when we let go of
one thousand dollars on an apartment sale (because it seems a small
percentage of the total) while bargaining hard to obtain a carpet at 40
instead of 50 dollars!

Higher mathematics must be constrained in a similar manner by our
evolutionary toolkit. Complex numbers, for instance, were deemed "imaginary"
and impossible to understand until a mathematician found that they could be
described intuitively as a plane - an easy-to-grasp concept for the brain.

COOK: What does this research tell us about how reading should be taught?
And does it tell us anything, more generally, about how best to educate?

DEHAENE: Both of my books, "The Number Sense" and "Reading in the Brain,"
point to the fact that young children are more competent than we think.
Learning is not "the furnishing of the mind's white paper," as John Locke
said. Even for an activity as novel as reading, we do not learn from
scratch, but by minimally changing our existing brain circuits, capitalizing
on their pre-existing structure. Thus, teachers and teaching methods should
pay more attention to the existing structure of the child's mind and brain.

In the case of reading, very concretely, as I explain in the book, we now
have plenty of evidence that the whole-language approach has nothing to do
with how our visual system recognizes written words - our brain never relies
on the overall contours of words, rather it decomposes all of its letters
and graphemes in parallel, subliminally and at a high speed, thus giving us
an illusion of whole-word reading. Experiments even suggest that the
whole-language method may orient learning towards the wrong brain region,
symmetrical to the visual word form area in the right hemisphere! We need to
inform our teaching with the best brain science - and we also need to
develop evidence-based education research, using classroom experiments to
verify that our deductions about teaching methods actually work in practice.

Theory, experiments on brain circuitry for reading, and education research
all currently point to the superiority of grapheme-phoneme teaching methods.

COOK: What is happening in the brain of a dyslexic? Are they reading
differently, or just more slowly?

DEHAENE: The dyslexic brain shows disorganized circuitry in the left
temporal lobe. In the majority of dyslexic children, the phonological
circuitry of the left hemisphere seems subtly disorganized, and this seems
to cause a failure to learn to properly interconnect visual letter
recognition with speech sounds. As a result, their visual word-form area
does not develop fully, or not at the normal speed, and they continue to
read serially, letter by letter or chunk by chunk, at an age where parallel
reading is well established in normal readers.

We should never forget, however, that there is a great heterogeneity in
dyslexia - so some children probably suffer from other difficulties, for
instance related to the spatial organization of the word. Some children
appear to mix left and right, or to be unable to focus on the letters
sequentially from left to right without error, and this might be an
additional cause of dyslexia, though somewhat less frequent that the
phonological problem.

COOK: And if the brain of a dyslexic is organized differently, does that
suggest that it might have other abilities -- or is dyslexia purely an

DEHAENE: This isn't fully known, but I was intrigued by recent research
which indicates that dyslexic children and adults can be better on tasks of
symmetry detection - they have a greater ability to notice the presence of
symmetrical patterns, and the evidence even suggests that this was helpful
in a group of astrophysicists to detect the symmetrical spectrum of black

My theory is that mirror recognition is one of the functions that we have
to partially "un-learn" when we learn to read - it is a universal feature of
the primate brain that is, unfortunately, inappropriate in our alphabet
where letters p, q, d and b abound. By somehow managing to maintain this
ability, dyslexics might be at some advantage in visual, spatial or even
mathematical tasks.

More generally, we are touching here on the very interesting issue of
whether cultural recycling makes us lose some abilities that were once
useful in our evolution. The brain is a finite system, so although there are
overwhelming benefits of education, there might also be some losses. We are
currently doing experiments with Amazon Indians, in part to test what are
their native abilities and whether, in some domains such as geometry and
spatial navigation, they might not be better than us.

COOK: Having done all this research, to you find yourself reading
differently now, or experiencing it differently?

DEHAENE: Not really - reading has become so automatic as to be
inconspicuous: as an expert reader, you concentrate on the message and no
longer realize the miracles that are worked out by your brain! I am always
in awe, however, when I watch young children decipher their first words -
the pride on their face is a living testimony to the wonders of reading.


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