About 5,000 years ago, societies in ancient
Sumeria, China and South America invented
writing, and in the millennia since, the ability
to read has propelled human intellectual and
cultural development, vastly expanding our
capacity to learn, create, explore and record
what we think, feel and know. Reading supplies
our brains with an external hard drive and gives
us access to our speciesʼs past: In the words of
Francisco de Quevedo, it enables us “to listen to
the dead with our eyes.”
But how, in such a short time, did the human
species evolve this unique skill, one that
requires the brain to decode written words visually
and process their sounds and sense rapidly?
In this fascinating and scholarly book, French
neuroscientist Stanislas Dehaene explains what
scientists now know about how the human brain
performs the feat of reading, and what made
this astonishing cultural invention biologically
possible.
Presented with a wordʼs image on the retina,
average readers of English can, within a few
10ths of a second, match it with one of 50,000
or more words stored in their mental dictionaries,
comprehend its meaning in context, and proceed
seamlessly to the next word. Amazingly,
most children become proficient readers during
elementary school (although learning to read
Italian is easier, and learning to read Chinese
harder, than learning to read English). In recent
years, new imaging techniques have allowed
researchers to watch normal brains in the act
of reading, and studies have shed light on why
the brains of dyslexic children, as well as those
of certain stroke victims, fail to process written
words successfully.
“Only a stroke of good fortune allowed us to
read,” Dehaene writes near the end of his tour
of the reading brain. It was Homo sapiensʼs
luck that in our primate ancestors, a region of
the brainʼs paired temporal lobes evolved over
a period of 10 million years to specialize in the
visual identification of objects. Experiments in
monkeys show that, within this area, individual
nerve cells are dedicated to respond to a specific
visual stimulus: a face, a chair, a vertical line.
Research suggests that, in humans, a corresponding
area evolved to become what Dehaene
calls the “letterbox,” responsible for processing
incoming written words. Located in the brainʼs
left hemisphere near the junction of the temporal
and occipital lobes, the letterbox performs identical
tasks in readers of all languages and scripts.
Like a switchboard, it transmits signals to multiple
regions concerned with wordsʼ sound and
meaning — for example, to areas that respond to
noun categories (people, animals, vegetables),
to parts of the motor cortex that respond to action
verbs (“kiss,” “kick”), even to cells in the
brainʼs associative cortex that home in on very
specific stimuli. (In one epileptic patient, for
example, a nerve cell was found that fired only
in response to images or the written name of
actress Jennifer Aniston!)
Children learn reading in a stepwise process:
first, awareness that words are made up of
phonemes or speech sounds (ba, da); then the
discovery that thereʼs a correspondence between
these speech sounds and pairs or groups
of letters. Later the child begins to recognize
entire words, and after a few years, reading
speed becomes independent of word length.
Dehaene deplores the whole-language approach
to teaching reading in which beginning readers
are presented with entire words or phrases
in the hope of fostering earlier comprehension
of text. He cites research showing that children
who first learn which sounds are represented by
which letters, and how pairs or groups of letters
correspond to speech sounds, make steadier
progress and achieve better reading scores than
those taught using the whole-language method.
He also notes the success of teaching methods
that incorporate multiple senses and motor gestures,
such as those used in Montessori schools.
For example, in preparation for learning to read,
young Montessori students are often asked to
trace with their fingers the shapes of large letters
cut out of sandpaper. The exercise makes use of
vision, touch and spatial orientation, as well as
mimicking the gestures used to print each letter.
Between 5 percent and 17 percent of U.S.
children suffer from dyslexia, or severe difficulty
in reading. The disorder runs in families and
probably has no single cause. Several susceptibility
genes have been identified, most of them
influencing the migration of nerve cells within
the developing brain of the fetus. Research
suggests that, even as infants, many dyslexic
children have trouble hearing the difference
between similar-sounding consonants such as
b and d; but about one in four dyslexics has
primarily visual difficulties with word-processing.
Although there is no prospect of a cure for
dyslexia, Dehaene points to promising results
with various intervention strategies aimed at
strengthening awareness of speech sounds and
letter differences. After dozens of hours of training
using such programs, Dehaene writes, the
majority of dyslexic children “end up reading
adequately, even if performance continues to lag
behind that of their peers.”
Reading, Dehaene writes, is “by far the finest
gem” in humanityʼs cultural storehouse, and
judging by the ubiquity of electronic messages
and Web surfing, itʼs a skill no less essential
in the digital age than it was during the age of
print.
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The Washington Post.