Reading in the Brain, book review of a new book by
By STANISLAS DEHAENE
Reviewed by Jonah Lehrer, jacket blurb by Dr Maryanne Wolf, Tufts University
Right now, your mind is performing an astonishing feat. Photons are
bouncing off these black squiggles and lines -- the letters in this
sentence -- and colliding with a thin wall of flesh at the back of
your eyeball. The photons contain just enough energy to activate
sensory neurons, each of which is responsible for a particular plot of
visual space on the page. The end result is that, as you stare at the
letters, they become more than mere marks on a page. You've begun to
read.
Seeing the letters, of course, is just the start of the reading
process. As the neuroscientist Stanislas Dehaene reveals in his
fascinating new book, Reading in the Brain, the real wonder is what
happens next. Although our eyes are focused on the letters, we quickly
learn to ignore them. Instead, we perceive whole words, chunks of
meaning. (The irregularities of English require such flexibility. As
George Bernard Shaw once pointed out, the word "fish" could also be
spelled ghoti, assuming that we used the gh from "enough," the o from
"women," and the ti from "lotion.") In fact, once we become proficient
at reading, the precise shape of the letters -- not to mention the
arbitrariness of the spelling -- doesn't even matter, which is why we
read word, WORD, and WoRd the same way.
In this clearly written summary of the field, Dehaene is primarily
interested in two separate mysteries. The first mystery is how the
individual human brain learns to read. What changes take place inside
our head between kindergarten and second grade, when most of us start
to take literacy for granted? How do we go from sounding out
syllables, carefully parsing the phonetics of each word, to becoming
fluent readers? And how does this incredibly complicated act become
automatic, so that evn ths sntnce cn b quikly undrstd?
Dehaene begins by introducing the reader to the "letterbox area," a
small bit of brain just behind the left ear. The crucial role of this
cortical part was first revealed by Mr. C, a 19th-century neurological
patient who, after a mild stroke, lost the ability to read. What made
Mr. C's case so peculiar is that his vision was perfectly fine; he
could make sense of objects and faces and even numbers. However, when
he opened up a book or glanced at a newspaper, the letters on the page
were utterly inscrutable, a mess of inchoate lines and curves. "He
[Mr.C] thinks that he has lost his mind," his doctor dryly noted.
Subsequent studies of patients with pure alexia -- they can see
everything but written language -- have located the specific contours
of the letterbox area. Not surprisingly, it takes up a significant
chunk of our visual cortex, as the invention of the alphabet seems to
have usurped brain cells previously devoted to object recognition.
(Dehaene refers to this process as "neuronal recycling.") He also
speculates that, while "learning to read induces massive cognitive
gains," it also comes with a hidden mental cost: because so much of
our visual cortex is now devoted to literacy, we're less able to
"read" the details of natural world.
But reading isn't just about seeing -- we still have to imbue those
syllabic sounds with meaning. This is why, once the letterbox area
deciphers the word -- this takes less than 150 milliseconds -- the
information is immediately sent to other brain areas, which help us
interpret the semantic content. Such a complex act requires a variety
of brain areas scattered across both hemispheres, all of which must
work together to make sense of a sentence. If any of these particular
areas are damaged, people tend to lose specific elements of language,
such as the ability to conjugate verbs or decipher metaphors.
One of the most intriguing findings of this new science of reading is
that the literate brain actually has two distinct pathways for
reading. One pathway is direct and efficient, and accounts for the
vast majority of reading comprehension -- we see a group of letters,
convert those letters into a word, and then directly grasp the word's
meaning. However, there's also a second pathway, which we use whenever
we encounter a rare and obscure word that isn't in our mental
dictionary. As a result, we're forced to decipher the sound of the
word before we can make a guess about its definition, which requires a
second or two of conscious effort.
The second major mystery explored by Dehaene is how reading came to
exist. It's a mystery that's only deepened by the recency of literacy:
the first alphabets were invented less than 4,000 years ago, appearing
near the Sinai Peninsula. (Egyptian hieroglyphic characters were used
to represent a Semitic language.) This means that our brain wasn't
"designed" for reading; we haven't had time to evolve a purpose-built
set of circuits for letters and words. As Deheane eloquently notes,
"Our cortex did not specifically evolve for writing. Rather, writing
evolved to fit the cortex."
Deheane goes on to provide a wealth of evidence showing this cultural
evolution in action, as written language tweaked itself until it
became ubiquitous. In fact, even the shape of letters -- their odd
graphic design -- has been molded by the habits and constraints of our
perceptual system. For instance, the neuroscientists Marc Changizi and
Shinsuke Shimojo have demonstrated that the vast majority of
characters in 115 different writing systems are composed of three
distinct strokes, which likely reflect the sensory limitations of
cells in the retina. (As Dehaene observes, "The world over, characters
appear to have evolved an almost optimal combination that can easily
be grasped by a single neuron.") The moral is that our cultural forms
reflect the biological form of the brain; the details of language are
largely a biological accident.
Deheane ends the book with a discussion of education -- he's a
supporter of phonics and ridicules the whole-language method, "which
does not fit with the architecture of our visual brain." It's an
interesting chapter, and it's always nice to see scientists grapple
with the practical implications of their work, but the most compelling
themes of the book remain rooted in basic science. As Deheane and
others have demonstrated, the brain is much more than the seat of the
soul -- it's also the fleshy source of our culture.
By studying the
wet stuff inside our head, we can begin to understand why this
sentence has this structure, and why this letter, this one right here,
has its shape.ED NOTE: Yes, Jonah, and why reading on paper surfaces is so different both mentally and emotionally from reading on screens, and this will be studied soon with MRI scans. Then we will know more about all this.
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