Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. For a short introduction to this book click on « intro.lecture » Contents : Introduction : The science of reading 1.How we read 2.The literal brain 3.The reading neurones 4.The invention of reading 5.Learning how to read 6.The dyslexic brain 7.Reading and symmetry 8.Towards cultivating neurones Conclusion : The future of reading And now, let’s take a quick look at the reading process from a neurophysiological point of view. Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. How do we read? Everything begins in the retina, where the photons which are reflected by the page are projected (p.36). The retina is the membrane which covers the back of the eyeball : it is made up of several layers of cells which have different functions. It receives the images which enter through the eye, transforms them into signals or electronic impuses and transmits them to the brain through the optic nerve. Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. The retina isn’t uniform, in the sense that only the central region of the retina, called the fovea, contains numerous high resolution photoreceptor cells, the cones. This region, which takes up only about 15 degrees of the visual field, is also the only area of the retina which is really useful for reading. It is the only area which can perceive letters with sufficient detail to allow them to be recognized (p.36). This can be illustrated as follows : The human eye and some of its components cristalline lens retina Message read «If the months and the days are eternal passengers, the years which follow on likewise travel. Whether one navigates on a skiff all one’s life or one pulls on the horse’s bit until the threshold of old age, every day is a voyage, and one makes one’s home of this voyage. I no longer know in which year a solitary cloud invited me into the wind, (...). cornea vitreous humour pupil (Bashô, 17th century Japanese poet.) iris fovea optic nerve Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. The fovea’s narrowness forces us to move our eyes constantly while we are reading. Moreover, we don’t read through a text in a single continuous process. Our eyes move in saccades (short rapid movements). This is due to the fact that in the centre of the fovea, visual information isn’t perceived with the same precision everywhere. (…) Precision is maximum in the center and diminishes towards the exterior. (p.37) Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. We identify 10 or 12 lettres per saccade : 3 or 4 to the left of the centre of fixation and 7 or 8 to the right. This is what is called the span of visual perception of letters. This asymmetry comes from the direction in which we read. A person who is reading Arabic or Hebrew, whose fixation goes from the right to the left, has an inverted span of visual perception (p.41). Our eye imposes enormous and irremovable constraints on reading. It has been proven that the ocular saccades are actually what limit our reading speed (p.42). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. When a word enters the retina, it breaks up into a thousand pieces : each part of the image on the page is recognized by a distinct photoreceptor. The difficulty resides in re-assembling the fragments in order to decode the letters which are involved, the order they are presented in, and the word which is in question. (p.35) Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Where does this take place ? In a certain part of the brain, there is the visual word recognition system : in each individual, in every culture in the world, the same cerebral region, give or take a few milimeters, intervenes to decode written words. Whether one reads in French or in Chinese, learning how to read always goes through an identical circuit (p. 27). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Our visual word recognition system perceives what doesn’t change despite the variety of forms which words can take (size, fonts, capital/small letters, bold type or not, underlined or not, …) : this is what is called unvariable word recognition. Examples : TWO, two, two, TWO, Two, … R, R, R, r, r, r Thus the system learns to ignore all variations which aren’t pertinent for reading and on the other hand, to locate and amplify pertinent differences, even tiny ones. Example : the difference between « live » et « love », between « seat » et « sate », … Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. How does this take place? Our visual system automatically breaks words down into their basic components. The nature of these components remains an ongoing subject of research (p.51). Example : unbuttonned It’s likely that multiple levels of analysis coexist (p. 51) : un button un Letters Graphemes Syllables Morphemes Words u n but b ut ned ton t ned on n ed Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Broken down in this way, these elements can then be used by the brain to give sound and sense. Two channels exist : - the phonological channel or the sound channel (= oralisation or silent reading : this doesn’t involve either articulating or moving one’s lips, but rather transforming the letters into sounds to reach the pronunciation of words). Also called grapheme-phoneme conversion. - the lexical channel or the direct channel which gives immediate access to meaning. Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. This is a very controversial subject, as scientists have differing opinions : - for some, it is impossible to reach meaning without first going through the phonological channel - for others, going through the phonological channel is a characteristic of a beginning reader and not of a good reader. The author’s position: Today a consensus is beginning to appear : for the adult, both channels of reading exist and are active simultaneously. (…) They therefore function on a parallel basis, one supporting the other (p.53). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. The phonological channel : the only possible way to read new or rare words with regular spelling, neologisms, … Decoding letters, then searching for possible pronunciation, then meaning. The lexical channel : used for common words and indispensable first for irregular words (numerous in French and even more so in English) Decoding letters, then searching for meaning, then pronunciation. Languages which are very rich in phonemes ! ≠ for Italian where there are almost no irregular words – each letter corresponds to a sound children’s reading scores are significantly better than for French children and there is almost no dyslexia! Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Neither of these channels, of itself, is sufficient for reading all words (p.70). When we read aloud, the two channels conspire together, as it were and collaborate with each other (p.70). Thus, most contemporary psychological models agree with the idea that expert and fluent reading is the result of close coordination between the two channels of reading (p. 71). Please note : it would be more correct to speak of the multiple channels of reading. Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Please note with respect to the lexical channel : It is based on the storage of tens of thousands of words in a « mental glossary » or rather in several glossaries : orthographic, phonological, grammatical, semantic. And all of these glossaries act in parallel and not at all sequentailly great efficiency and rapidity ! (see pages 74 and following for the pandemonium metaphor). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Without the action of our mental glossary, the written word would remain « a dead letter ». The identification of letters and words is an active decoding process during which the brain adds information to the visual signal (p.80). In order for a word to be recognized, the multiple cerebral systems have to agree on an unequivocal interpretation of the visual input. The time that it takes us to read a word, therefore, depends less on its intrinsic characteristics than on the conflicts or coalitions that it induces within our cerebral architecture (p. 82). Our glossary is like an arena where there is strong competition and where the advantage goes to the « regulars », that is to say, the words used most frequently (p. 82). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. In short, in the brain : Each lobe specializes in one or several sensorial functions. VISION TASTE OLFACTION HEARING Left hemisphere : external view Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. The information (words, faces, objects, …) perceived by the eyes, activates the visual areas of the occipital lobe in each hemisphere. L R L R These regions make a primary analysis of the image, probably in order to extract the elementary forms (lines, curves, surfaces, …) . At this stage of information processing, the brain doesn’t yet know what kind of stimulus it is dealing with (p. 115). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Then (50 milliseconds later), the information begins to be sorted and the words give rise to the activation of the word recognition area which we have just spoken about (especially in the left hemisphere, in the ventral occipitotemporal region). All of this happens automatically, in less than fifth of a second ! a And after visual recognition, what path does reading take ? How do we have access to the sense and the sound of words ? Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. The occipito-temporal region which we have just spoken about then distributes information to numerous cortical regions. In two principal circuits : one which converts the information into sounds, the other which gives it meaning. These regions are not specifically for reading. And these two channels for reading (which give access to the meaning and the sound of words) activate distinct cerebral areas. Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Conversion of letters into sounds : The left temporal lobe is largely implicated, notably an upper region of the lobe which is called the temporal plane. Because it allows visual and auditive information to meet, the temporal plane very likely plays a role of essential junction in the process of learning how to read (p. 152). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Means of access to meaning : Several regions are activated, none of which is specific for written words. The complexity of these mechanisms is such that it is impossible to summarize in just a few lines ! We are just at the beginning of the neurology of meaning. (…) In the area of meaning, humility is necessary, because no one, for the moment, can claim to have a precise neurological model of this mysterious flash of understanding which means that the activity of a network of neurones, all of a sudden, « makes sense » (p.155). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. We know at least one thing, that it would be naive to think that meaning is limited to a small number of cerebral regions. On the contrary, semantics calls on very vast populations of neurones distributed in all of the regions of the cortex (p.156). And in chapter 5, entitled « Learning how to read » the author shows the ways in which learning how to read modifies a child’s brain; he describes the phases of this learning process and suggests directions to follow to optimize the teaching of reading. Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Notably, he demonstrates the inefficiency of the global method : To sum up, today there can no longer be any doubt : the global outline of words plays practically no role in reading. Visual recognition of words is not based on a global perception of its outline, but on breaking it down into simple elements, letters and graphemes. The cortical region of the visual form of words handles all of the letters of the word in parallel, which is responsible, historically, for the impression of global reading. But the immediacy of reading is merely an illusion, caused by the extreme automatization of the different steps, which takes place outside of our awareness (p. 297). Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. To conclude this overview, we would like to highlight in chapter 6 where the author speaks about dyslexia : In the majority of cases, dyslexia can be linked to a faulty mental manipulation of phonemes. Dyslexic children’s brains present several characteristic anomalies : (…). Do these anomalies imply that dyslexia is incurable ? Not at all. (…) (p.309) Paper and Microsoft Power Point Presentation 2003 by Hélène Delvaux for the IF Belgiim Images : clipart at http://office.microsoft.com For the European project Signesetsens 2009 Stanislas DEHAENE, Les neurones de la lecture, Odile Jacob, 2007. Some introductory words : P. 1/4 Behind each reader there is hidden a neuronal mechanism which is admirable for its precision and efficiency, the organisation of which we are beginning to understand. During the last twenty years an authentic science of reading has been born (p.21). In this fascinating and remarkably clear book, the author tries to share this science of reading, as well as the experimental progress which supports it. He hopes to see the appearance of a true educational neuroscience which would allow for the optimization of teaching strategies ( by permanently setting aside certain methods used to teach reading, such as, for example, the method which is known as the global method, which he has shown to be inefficient because it isn’t adapted to a child’s cerebral organisation). There are two opposing models used to « explain » the brain : the old model, that of generalized plasticity and cultural relativity, and the new one, which the author defends, that of neuronal recycling. P. 2/4 The old model develops the following ideas : • The brain is a completely flexible and malleable organ ; therefore it poses no constraints on the full range of human activities (p.26). • The human brain is a sort of clean slate on which natural and cultural data from the environment are imprinted. There is thus no biological human nature, but a progressive construction of human nature through immersion in a given culture. • It is only the capacity to learn which is characteristic of our human nature (p.26-27) This model has been challenged by recent data from cerebral imagery and from neuropsychology. We shall see to what extent the image of an infinitely malleable brain, like a clean slate, and which would limit itself to absorbing information from its cultural environment, is false (p.27). P. 3/4 The author develops another model, that of neuronal recycling. Of course our brain is capable of learning and shows plasticity and the ability to adapt to the environment, he says, but its architecture is strictly managed by strong genetic constraints. (p.27) This learning is therefore limited. For example, in each individual, in every culture in the world, the same cerebral region, give or take a few milimeters, intervenes to decode written words. Whether one reads in French or in Chinese, learning how to read always goes through an identical circuit (p. 27). This model is largely based on the idea that our cortical circuits, inherited from our evolving past, adapt as best they can to reading : learning how to read imposes profound modifications on brain circuits (pp. 22-23). The brain is a highly structured organ which makes new things out of old. To learn new competencies, we recycle our old cerebral circuits of primates – to the extent that these tolerate a minimum of change (p.28). P. 4/4 The paradox of reading underlines the indubitable fact that our genes haven’t evolved so as to allow us to learn how to read. I only see one solution. If the brain hasn’t had the time to evolve under the pressure of the constraints imposed by what is written, then it is what is written which has evolved to take into account the constraints of our brains (p.29). And a bit further along, the author finds the traces of an unceasing, evolving construction which relentlessly adapts the written objects to our brains’ constraints. Please note : reading in this book is only directed towards reading words and not images.