Stanislas Dehaene holds the chair of experimental cognitive psychology at the Collège de France, and he is also director of the INSERM-CEA Cognitive Neuroimaging Unit at NeuroSpin, the most advanced neuroimaging research center in France. Dehaene is best known for his research into the cerebral basis of numbers, popularized in his book The Number Sense: How the Mind Creates Mathematics (Oxford University Press, 1999). In his new book, Reading in the Brain: The Science and Evolution of a Human Invention (Viking Adult, 2009), 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. Mind Matters editor Gareth Cook recently talked with Dehaene about how the art of reading reveals the fundamental relationship between our cultural inventions and our evolved brain.
SCIENTIFIC AMERICAN MIND: How did you become interested in the neuroscience of reading?
STANISLAS DEHAENE: One of my longtime 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 on our children’s brains. The impact that it has on us is tantalizing. Reading raises very fundamental issues of how the brain and culture interact.
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As I started to do experimental research in this domain, using the different tools at my disposal—from behavior of patients, functional magnetic resonance imaging [fMRI], changes in electrical activity measured by electroencephalography [EEG] and even intracranial electrodes embedded under the skull—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 that the brain obviously did not evolve for that purpose. The search for an answer resulted in this book. In the end, reading forces us to propose a very different relationship between culture and the brain.
MIND: How does this new relationship differ from more traditional views of culture and the brain?
DEHAENE: A classical, though often implicit, view in social science is that the human brain, unlike that of other animals, is a learning machine that can adapt to essentially any novel cultural task, however complex. If this idea is correct, 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” is not novel. It is deeply related to the structuralist view of anthropology, as exemplified by the late Claude Lévi-Strauss, which posits that any cultural phenomenon can be understood in terms of certain structures that are ubiquitous around the world. What I am proposing is that the universal structures that recur across cultures—mythology, marriage traditions, language—are, in fact, ultimately traceable to specific brain systems.
In the case of reading, the shapes of our writing systems have evolved toward a progressive simplification while remaining compatible with the visual-coding scheme that is present in all primate brains. A fascinating discovery, made by American neuroscientist Marc Changizi of the Rensselaer Polytechnic Institute, is that all the world’s writing systems use the same set of basic shapes. Recordings of neurons in macaques show that several of 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 these naturally occurring shapes, including T, L and Y. We merely “recycle” these shapes (and the corresponding part of the cortex) and turn them into a cultural code for language. [For more on Changizi’s work, see “Origins,” by Melinda Wenner; Reviews, Scientific American Mind, July/August 2009.]
MIND: In your new book, you describe a part of the brain as the “letterbox.” Can you please explain what you mean by that?
DEHAENE: The letterbox, also called the “visual word-form area” in the scientific literature, is the nickname 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 a broader set of visual areas that help 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.
MIND: 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 lighting or other superficial variations).
We are starting to do brain-imaging experiments in people who are illiterate, 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 that 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.
MIND: How might our brain’s abilities and limits shape other activities such as 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 already possess it in the first few months of life. But it is only approximate and nonsymbolic—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 counting 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 $1,000 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!
Higher mathematics must be constrained in a similar manner by our evolutionary tool kit. Complex numbers, for instance, were deemed “imaginary” and impossible to understand until a mathematician found that they could be described intuitively on a plane—an easy-to-grasp concept for the brain.
MIND: 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 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 preexisting 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—in which children are taught entire words rather than graphemes (letters) and phonemes (fundamental sounds such as “th”)—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 a word’s letters 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 toward the wrong brain region, one in the right hemisphere that is symmetrical to the left hemisphere visual word-form area—the letterbox.
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.
MIND: What is happening in the brain of dyslexics? Are they reading differently or simply more slowly?
DEHAENE: The dyslexic brain shows disorganized circuitry in the left temporal lobe. In most 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 it does not develop at the normal speed. 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 great variation 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 than the phonological problem.
MIND: And if the brain of a dyslexic is organized differently, does that suggest it might have other abilities—or is dyslexia purely an impairment?
DEHAENE: The answer is not fully known, but I was intrigued by recent research indicating that dyslexic children and adults can perform better on tasks of symmetry detection—they have a greater ability to notice the presence of symmetrical patterns. The evidence even suggests that this skill was helpful in a group of astrophysicists to detect the symmetrical spectrum of black holes!
My theory is that mirror recognition is one of the functions that we have to partially “unlearn” when we learn to read—it is a universal feature of the primate brain that is, unfortunately, inappropriate in our alphabet where letters such as 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 the cultural “recycling” of brain areas 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 their native abilities are and whether, in some domains such as geometry and spatial navigation, they might not be better than us.
MIND: Having done all this research, do 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.
