Laurent Cohen & Stanislas Dehaene Publications on reading, pure alexia & VWFA

Laurent Cohen

Department of Neurology, 
Hopital de la Salpetriere,


Stanislas Dehaene

Universite Paris 11, Orsay, France









Selected references on reading, pure alexia, and the Visual Word Form Area  

 Dehaene, S. & Cohen, L. (2011). The unique role of the visual word form area in reading. Trends in Cognitive Sciences, 15, 254-262.
Notes: Reading systematically activates the left lateral occipitotemporal sulcus, at a site known as the visual word form area (VWFA). This site is reproducible across individuals/scripts, attuned to reading-specific processes, and partially selective for written strings relative to other categories such as line drawings. Lesions affecting the VWFA cause pure alexia, a selective deficit in word recognition. These findings must be reconciled with the fact that human genome evolution cannot have been influenced by such a recent and culturally variable activity as reading. Capitalizing on recent functional magnetic resonance imaging experiments, we provide strong corroborating evidence for the hypothesis that reading acquisition partially recycles a cortical territory evolved for object and face recognition, the prior properties of which influenced the form of writing systems
Institut National de la Sante et de la Recherche Medicale, Cognitive Neuroimaging Unit, Gif sur Yvette, 91191 France; Commissariat a l'Energie Atomique, Division of Life Sciences, Institute of Bioimaging, Neurospin, Gif sur Yvette, 91191 France; Universite Paris 11, Orsay, France; College de France, 11 Place Marcelin Berthelot, 75005 Paris, France

Pegado, F., Nakamura, K., Cohen, L., & Dehaene, S. (2011). Breaking the symmetry: mirror discrimination for single letters but not for pictures in the Visual Word Form Area. NeuroImage, 55, 742-749.
Notes: Humans and primates can quickly recognize mirror images of previously exposed pictures. This spontaneous mirror invariance, though advantageous for visual recognition, makes it difficult to distinguish the orientation of letters (e.g. to differentiate a "b" from a "d"), and may result in classical mirror reading and writing errors in preschoolers. Mirror invariance must therefore be overcome during reading acquisition. The Visual Word Form Area (VWFA), a region in the ventral stream that develops with reading expertise, was previously shown to discriminate words from their mirror images in literate adults. Here we investigate whether this region underlies mirror-image discrimination at the most elementary level of the orthographic code, the single-letter level. Using an fMRI priming paradigm, we demonstrate that the VWFA distinguishes the left-right orientation of single letters in skilled readers, and yet exhibits mirror invariance for simple pictures of matched complexity. These results clarify how letter shapes, after reading acquisition, escape the process of mirror invariance which is a basic property of the ventral visual shape recognition pathway
INSERM, U992, Cognitive Neuroimaging Unit, Gif/Yvette, France.

Szwed, M., Dehaene, S., Kleinschmidt, A., Eger, E., Valabregue, R., Amadon, A. et al. (2011). Specialization for written words over objects in the visual cortex. NeuroImage, 56, 330-344.
Notes: The Visual Word Form Area (VWFA) is part of the left ventral visual stream that underlies the invariant identification of visual words. It remains debated whether this region is truly selective for words relative to common objects; why this particular part of the visual system is reproducibly engaged in reading; and whether reading expertise also relies on perceptual learning within earlier visual areas. In this fMRI study we matched written words and line-drawings of objects in luminance, contour length and number of features. We then compared them to control images made by scrambling procedures that kept local features intact. Greater responses to written words than to objects were found not only in the VWFA, but also in areas V1/V2 and V3v/V4. Furthermore, by contrasting stimuli reduced either to line junctions (vertices) or to line midsegments, we showed that the VWFA partially overlaps with regions of ventral visual cortex particularly sensitive to the presence of line junctions that are useful for object recognition. Our results indicate that preferential processing of written words can be observed at multiple levels of the visual system. It is possible that responses in early visual areas might be due to some remaining differences between words and controls not eliminated in the present stimuli. However, our results concur with recent comparisons of literates and illiterates and suggest that these early visual activations reflect the effects of perceptual learning under pressure for fast, parallel processing that is more prominent in reading than other visual cognitive processes
INSERM U992, Cognitive Neuroimaging Unit, Gif sur Yvette, France.

Dehaene, S., Nakamura, K., Jobert, A., Kuroki, C., Ogawa, S., & Cohen, L. (2010). Why do children make mirror errors in reading? Neural correlates of mirror invariance in the visual word form area. NeuroImage, 49, 1837-1848.
Notes: Young children often make mirror errors when learning to read and write, for instance writing their first name from right to left in English. This competence vanishes in most adult readers, who typically cannot read mirror words but retain a strong competence for mirror recognition of images. We used fast behavioral and fMRI repetition priming to probe the brain mechanisms underlying mirror generalization and its absence for words in adult readers. In two groups of French and Japanese readers, we show that the left fusiform visual word form area, a major site of learning during reading acquisition, simultaneously shows a maximal effect of mirror priming for pictures and an absence of mirror priming for words. Thus, learning to read recruits an area which possesses a property of mirror invariance, seemingly present in all primates, which is deleterious for letter recognition and may explain children's transient mirror errors
INSERM, Cognitive Neuroimaging Unit, Gif sur Yvette 91191, France.

Qiao, E., Vinckier, F., Szwed, M., Naccache, L., Valabregue, R., Dehaene, S. et al. (2010). Unconsciously deciphering handwriting: subliminal invariance for handwritten words in the visual word form area. NeuroImage, 49, 1786-1799.
Notes: Expert readers exhibit a remarkable ability to recognize handwriting, in spite of enormous variability in character shape-a competence whose cerebral underpinnings are unknown. Subliminal priming, combined with neuroimaging, can reveal which brain areas automatically compute an invariant representation of visual stimuli. Here, we used behavioral and fMRI priming to study the areas involved in invariant handwritten word recognition. Compared to printed words, easily readable handwritten words caused additional activity in ventral occipitotemporal cortex, particularly in the right hemisphere, while difficult handwriting also mobilized an attentional parietofrontal network. Remarkably, however, subliminal repetition effects were observed across printed and handwritten styles, whether easy or difficult to read, both behaviorally and in the activation of the left visual word form area (VWFA). These results indicate that the left inferotemporal VWFA possesses an unsuspected degree of fast and automatic visual invariance for handwritten words, although surprisingly this invariance can be reflected both as repetition suppression and as repetition enhancement
INSERM, Cognitive Neuro-imaging Unit, IFR 49, Gif sur Yvette, France

Cohen, L., Dehaene, S., Vinckier, F., Jobert, A., & Montavont, A. (2008). Reading normal and degraded words: contribution of the dorsal and ventral visual pathways. NeuroImage, 40, 353-366.
Notes: Department of Neurology I, AP-HP, Hopital de la Salpetriere, 47/83 Boulevard de l'Hopital, Paris CEDEX 13, France.
Fast, parallel word recognition, in expert readers, relies on sectors of the left ventral occipito-temporal pathway collectively known as the visual word form area. This expertise is thought to arise from perceptual learning mechanisms that extract informative features from the input strings. The perceptual expertise hypothesis leads to two predictions: (1) parallel word recognition, based on the ventral visual system, should be limited to words displayed in a familiar format (foveal horizontal words with normally spaced letters); (2) words displayed in formats outside this field of expertise should be read serially, under supervision of dorsal parietal attention systems. We presented adult readers with words that were progressively degraded in three different ways (word rotation, letter spacing, and displacement to the visual periphery). Behaviorally, we identified degradation thresholds above which reading difficulty increased non-linearly, with the concomitant emergence of a word length effect on reading latencies reflecting serial reading strategies. fMRI activations were correlated with reading difficulty in bilateral occipito-temporal and parietal regions, reflecting the strategies required to identify degraded words. A core region of the intraparietal cortex was engaged in all modes of degradation. Furthermore, in the ventral pathway, word degradation led to an amplification of activation in the posterior visual word form area, at a level thought to encode single letters. We also found an effect of word length restricted to highly degraded words in bilateral occipitoparietal regions. Those results clarify when and how the ventral parallel visual word form system needs to be supplemented by the deployment of dorsal serial reading strategies

Epelbaum, S., Pinel, P., Gaillard, R., Delmaire, C., Perrin, M., Dupont, S. et al. (2008). Pure alexia as a disconnection syndrome: new diffusion imaging evidence for an old concept. Cortex, 44, 962-974.
Notes: Functional neuroimaging and studies of brain-damaged patients made it possible to delineate the main components of the cerebral system for word reading. However, the anatomical connections subtending the flow of information within this network are still poorly defined. Here we study the connectivity of the Visual Word Form Area (VWFA), a pivotal component of the reading network achieving the invariant identification of letter strings, and reproducibly located in the left lateral occipitotemporal sulcus. Diffusion images and functional imaging data were gathered in a patient who developed pure alexia following a small surgical lesion in the vicinity of his VWFA. We had a unique opportunity to compare images obtained before, early after, and late after surgery. Analysis of diffusion images with white matter tractography and voxel-based morphometry showed that the VWFA was mainly linked to the occipital cortex through the inferior longitudinal fasciculus (ILF), and to perisylvian language areas (supramarginal gyrus) through the arcuate fasciculus. After surgery, we observed the progressive and selective degeneration of the ILF, while the VWFA was anatomically intact. This allowed us to establish the critical causal role of this fiber tract in normal reading, and to show that its disruption is one pathophysiological mechanism of pure alexia, thus clarifying a long-standing debate on the role of disconnection in neurocognitive disorders
Hopital de la Salpetriere, Department of Neurology, Paris, France

Gaillard, R., Naccache, L., Pinel, P., Clemenceau, S., Volle, E., Hasboun, D. et al. (2006). Direct intracranial, FMRI, and lesion evidence for the causal role of left inferotemporal cortex in reading. Neuron, 50, 191-204.
Notes: Models of the "visual word form system" postulate that a left occipitotemporal region implements the automatic visual word recognition required for efficient reading. This theory was assessed in a patient in whom reading was explored with behavioral measures, fMRI, and intracranial local field potentials. Prior to surgery, when reading was normal, fMRI revealed a normal mosaic of ventral visual selectivity for words, faces, houses, and tools. Intracranial recordings demonstrated that the left occipitotemporal cortex responded with a short latency to conscious but also to subliminal words. Surgery removed a small portion of word-responsive occipitotemporal cortex overlapping with the word-specific fMRI activation. The patient developed a marked reading deficit, while recognition of other visual categories remained intact. Furthermore, in the post-surgery fMRI map of visual cortex, only word-specific activations disappeared. Altogether, these results provide direct evidence for the causal role of the left occipitotemporal cortex in the recognition of visual words
INSERM, U562, CEA/DSV, IFR 49, Orsay, France

Dehaene, S., Cohen, L., Sigman, M., & Vinckier, F. (2005). The neural code for written words: a proposal. Trends in Cognitive Sciences, 9, 335-341.
Notes: INSERM unit 562, Cognitive Neuroimaging, Service Hospitalier Frederic Joliot, CEA/DRM/DSV 4 Place du General Leclerc, 91401 Orsay cedex, France.
How is reading, a cultural invention, coded by neural populations in the human brain? The neural code for written words must be abstract, because we can recognize words regardless of their location, font and size. Yet it must also be exquisitely sensitive to letter identity and letter order. Most existing coding schemes are insufficiently invariant or incompatible with the constraints of the visual system. We propose a tentative neuronal model according to which part of the occipito-temporal 'what' pathway is tuned to writing and forms a hierarchy of local combination detectors sensitive to increasingly larger fragments of words. Our proposal can explain why the detection of 'open bigrams' (ordered pairs of letters) constitutes an important stage in visual word recognition.

Henry, C., Gaillard, R., Volle, E., Chiras, J., Ferrieux, S., Dehaene, S. et al. (2005). Brain activations during letter-by-letter reading: a follow-up study. Neuropsychologia, 43, 1983-1989.
Notes: Service de Neurologie 1, IFR 70, Hopital de la Salpetriere, AP-HP, 47/83 Bd de l'Hopital, 75651 Paris Cedex 13, France
Lesions affecting the ventral cortex of the left temporal lobe commonly yield a selective reading impairment known as pure alexia. It is thought to result from the disruption or deafferentation of the Visual Word Form Area (VWFA), a region in the left lateral occipitotemporal sulcus activated whenever normal subjects are viewing alphabetic strings. Most pure alexic patients retain the ability to identify single letters, and develop a strategy of letter-by-letter (LBL) reading. We recently studied fMRI activations in LBL readers and clarified the underlying mechanisms. However, LBL reading is a dynamic process which may improve over months or years of practice, although the cerebral bases of this continuing improvement are currently unknown. We had the opportunity to run the same behavioural testing and fMRI experiment a second time in an alexic patient, 8 months after collecting the data reported by Cohen et al. [Cohen, L., Henry, C., Dehaene, S., Molko, N., Lehericy, S., Martinaud, O., Lemer, C., and Ferrieux, S. (2004). The pathophysiology of letter-by-letter reading. Neuropsychologia, 42, 1768-1780]. We analyze the changes that occurred over this period in the pattern of reading-related activations, while the patient's LBL reading improved. The activation level decreased in most of the overall network between the two sessions. This general trend contrasted with a focal increase restricted to specific left frontal and parietal areas. When studying the contrast between words and consonant strings, which may be taken as a correlate of LBL reading, we also found a general decrease, except for similar left frontal and parietal regions, which showed a significant increase. We suggest that the pattern of evolution fits with the minimal hypothesis of normal strategic abilities and skill learning, associated with perceptual tuning in right-hemispheric structures able to substitute the disrupted VWFA

Cohen, L., Henry, C., Dehaene, S., Martinaud, O., Lehericy, S., Lemer, C. et al. (2004). The pathophysiology of letter-by-letter reading. Neuropsychologia, 42, 1768-1780.
Notes: Institut de Neurologie, Hopital de la Salpetriere, 47/83 Bd de l'Hopital, 75651 Paris CEDEX 13, France.
Pure alexia is a frequent and incapacitating consequence of left occipitotemporal lesions. It is thought to result from the disruption or the disconnection of the visual word form area (VWFA), a region reproducibly located within the left occipito-temporal sulcus, and encoding the abstract identity of strings of visual letters. Alexic patients often retain effective single letter recognition abilities, and develop an effortful letter-by-letter reading strategy which is the basis of most rehabilitation techniques. We study a patient who developed letter-by-letter reading following the surgical removal of left occipito-temporal regions. Using anatomical and functional MRI in the patient and in normal controls, we show that alexia resulted from the deafferentation of left fusiform cortex, and we analyze the network of brain regions subtending letter-by-letter reading. We propose that during letter-by-letter reading (1) letters are identified in the intact right-hemispheric visual system, with a central role for the region symetrical to the VWFA; (2) letters are serially transferred to the left hemisphere through the intact segment of the corpus callosum; (3) word identity is eventually recovered in the left hemisphere through verbal working memory processes involving inferior frontal and supramarginal cortex.

Cohen, L., Lehericy, S., Henry, C., Bourgeois, M., Larroque, C., Sainte-Rose, C. et al. (2004). Learning to read without a left occipital lobe: right-hemispheric shift of visual word form area. Annals of Neurology, 56, 890-894.
Notes: Institut de Neurologie, Hopital de la Salpetriere, AP-HP, Paris, France.
Using anatomical and functional magnetic resonance imaging, we studied the pattern of brain lateralization during spoken and written language tasks, in an 11-year-old girl who underwent a left occipitotemporal resection for a Sturge-Weber angioma at the age of 4 years, that is, after the development of speech but before the acquisition of reading. We observed a selective and successful shift to the right hemisphere of the visual component of reading, particularly the Visual Word Form Area, whereas the verbal components remained strongly left-lateralized. This emphasizes the potential utility of a precise functional and developmental cartography of language for the surgical treatment of focal brain lesions in children

Cohen, L., Jobert, A., Le Bihan, D., & Dehaene, S. (2004). Distinct unimodal and multimodal regions for word processing in the left temporal cortex. NeuroImage, 23, 1256-1270.
Notes: Institut de Neurologie, Hopital de la Salpetriere, AP-HP, Paris, France.
How are word recognition circuits organized in the left temporal lobe? We used functional magnetic resonance imaging (fMRI) to dissect cortical word-processing circuits using three diagnostic criteria: the capacity of an area (1) to respond to words in a single modality (visual or auditory) or in both modalities, (2) to modulate its response in a top-down manner as a function of the graphemic or phonemic emphasis of the task, and (3) to show repetition suppression in response to the conscious repetition of the target word within the same sensory modality or across different modalities. The results clarify the organization of visual and auditory word-processing streams. In particular, the visual word form area (VWFA) in the left occipitotemporal sulcus appears strictly as a visual unimodal area. It is, however, bordered by a second lateral inferotemporal area which is multimodal [lateral inferotemporal multimodal area (LIMA)]. Both areas might have been confounded in past work. Our results also suggest a possible homolog of the VWFA in the auditory stream, the auditory word form area, located in the left anterior superior temporal sulcus

Cohen, L. & Dehaene, S. (2004). Specialization within the ventral stream: the case for the visual word form area. NeuroImage, 22, 466-476.
Notes: Is there specialization for visual word recognition within the visual ventral stream of literate human adults? We review the evidence for a specialized "visual word form area" and critically examine some of the arguments recently placed against this hypothesis. Three distinct forms of specialization must be distinguished: functional specialization, reproducible localization, and regional selectivity. Examination of the literature with this theoretical division in mind indicates that reading activates a precise subpart of the left ventral occipitotemporal sulcus, and that patients with pure alexia consistently exhibit lesions of this region (reproducible localization). Second, this region implements processes adequate for reading in a specific script, such as invariance across upper- and lower-case letters, and its lesion results in the selective loss of reading-specific processes (functional specialization). Third, the issue of regional selectivity, namely, the existence of putative cortical patches dedicated to letter and word recognition, cannot be resolved by positron emission tomography or lesion data, but requires high-resolution neuroimaging techniques. The available evidence from single-subject fMRI and intracranial recordings suggests that some cortical sites respond preferentially to letter strings than to other categories of visual stimuli such as faces or objects, though the preference is often relative rather than absolute. We conclude that learning to read results in the progressive development of an inferotemporal region increasingly responsive to visual words, which is aptly named the visual word form area (VWFA)

Cohen, L., Martinaud, O., Lemer, C., Lehericy, S., Samson, Y., Obadia, M. et al. (2003). Visual word recognition in the left and right hemispheres: anatomical and functional correlates of peripheral alexias. Cerebral Cortex, 13, 1313-1333.
Notes: Institut de Neurologie, Hopital de la Salpetriere, AP-HP, Paris, France.
According to a simple anatomical and functional model of word reading, letters displayed in one hemifield are first analysed through a cascade of contralateral retinotopic areas, which compute increasingly abstract representations. Eventually, an invariant representation of letter identities is created in the visual word form area (VWFA), reproducibly located within the left occipito-temporal sulcus. The VWFA then projects to structures involved in phonological or lexico-semantic processing. This model yields detailed predictions on the reading impairments that may follow left occipitotemporal lesions. Those predictions were confronted to behavioural, anatomical and functional MRI data gathered in normals and in patients suffering from left posterior cerebral artery infarcts. In normal subjects, alphabetic stimuli activated both the VWFA and the right-hemispheric symmetrical region (R-VWFA) relative to fixation, but only the VWFA showed a preference for alphabetic strings over simple chequerboards. The comparison of normalized brain lesions with reading-induced activations showed that the critical lesion site for the classical syndrome of pure alexia can be tightly localized to the VWFA. Reading impairments resulting from deafferentation of an intact VWFA from right- or left-hemispheric input were dissected using the same methods, shedding light on the connectivity of the VWFA. Finally, the putative role of right-hemispheric processing in the letter-by-letter reading strategy was clarified. In a letter-by-letter reader, the R-VWFA assumed some of the functional properties normally specific to the VWFA. These data corroborate our initial model of normal word perception and underline that an alternative right-hemispheric pathway can underlie functional recovery from alexia

McCandliss, B. D., Cohen, L., & Dehaene, S. (2003). The visual word form area: Expertise for reading in the fusiform gyrus. Trends in Cognitive Sciences, 7, 293-299.
Notes: B.D. McCandliss, Sackler Inst. Devmtl. Psychobiology, Weill Med. Coll. of Cornell Univ., Box 140, 1300 York Avenue, New York, NY 10021
Brain imaging studies reliably localize a region of visual cortex that is especially responsive to visual words. This brain specialization is essential to rapid reading ability because it enhances perception of words by becoming specifically tuned to recurring properties of a writing system. The origin of this specialization poses a challenge for evolutionary accounts involving innate mechanisms for functional brain organization. We propose an alternative account, based on studies of other forms of visual expertise (i.e. bird and car experts) that lead to functional reorganization. We argue that the interplay between the unique demands of word reading and the structural constraints of the visual system lead to the emergence of the Visual Word Form Area

Cohen, L., Lehericy, S., Chochon, F., Lemer, C., Rivaud, S., & Dehaene, S. (2002). Language-specific tuning of visual cortex? Functional properties of the Visual Word Form Area. Brain, 125, 1054-1069.
Notes: Institut de Neurologie, Hopital de la Salpetriere, AP-HP, Paris, France.
The first steps in the process of reading a printed word belong to the domain of visual object perception. They culminate in a representation of letter strings as an ordered set of abstract letter identities, a representation known as the Visual Word Form (VWF). Brain lesions in patients with pure alexia and functional imaging data suggest that the VWF is subtended by a restricted patch of left-hemispheric fusiform cortex, which is reproducibly activated during reading. In order to determine whether the operation of this Visual Word Form Area (VWFA) depends exclusively on the visual features of stimuli, or is influenced by language-dependent parameters, brain activations induced by words, consonant strings and chequerboards were compared in normal subjects using functional MRI (fMRI). Stimuli were presented in the left or right visual hemifield. The VWFA was identified in both a blocked-design experiment and an event-related experiment as a left-hemispheric inferotemporal area showing a stronger activation to alphabetic strings than to chequerboards, and invariant for the spatial location of stimuli. In both experiments, stronger activations of the VWFA to words than to strings of consonants were observed. Considering that the VWFA is equally activated by real words and by readable pseudowords, this result demonstrates that the VWFA is initially plastic and becomes attuned to the orthographic regularities that constrain letter combination during the acquisition of literacy. Additionally, the use of split-field stimulation shed some light on the cerebral bases of the classical right visual field (RVF) advantage in reading. A left occipital extrastriate area was found to be activated by RVF letter strings more than by chequerboards, while no symmetrical region was observed in the right hemisphere. Moreover, activations in the precuneus and the left thalamus were observed when subjects were reading RVF versus left visual field (LVF) words, and are likely to reflect the attentional component of the RVF advantage

Dehaene, S., Le Clec'H, G., Poline, J. B., Le Bihan, D., & Cohen, L. (2002). The visual word form area: a prelexical representation of visual words in the fusiform gyrus. Neuroreport, 13, 321-325.
Notes: Unite INSERM 334, France
Event-related fMRI was used to test the hypothesis that the visual word form area in the left fusiform gyrus holds a modality-specific and prelexical representation of visual words. Subjects were engaged in a repetition-detection task on pairs of words or pronounceable pseudo-words that could be written or spoken. The visual word form area responded only to written stimuli, not to spoken stimuli, independently of their semantic content. We propose that the occasional activation of the fusiform gyrus when listening to spoken words is due to the topdown recruitment of visual orthographic or object representations

Molko, N., Cohen, L., Mangin, J. F., Chochon, F., Lehericy, S., Le Bihan, D. et al. (2002). Visualizing the neural bases of a disconnection syndrome with diffusion tensor imaging. Journal of Cognitive Neuroscience, 14, 629-636.
Notes: INSERM, Service Hospitalier Frederic Joliot, Orsay cedex, France
Disconnection syndromes are often conceptualized exclusively within cognitive box-and-arrow diagrams unrelated to brain anatomy. In a patient with alexia in his left visual field resulting from a posterior callosal lesion, we illustrate how diffusion tensor imaging can reveal the anatomical bases of a disconnection syndrome by tracking the degeneration of neural pathways and relating it to impaired fMRI activations and behavior. Compared to controls, an abnormal pattern of brain activity was observed in the patient during word reading, with a lack of activation of the left visual word form area (VWFA) by left hemifield words. Statistical analyses of diffusion images revealed a damaged fiber tract linking the left ventral occipito-temporal region to its right homolog across the lesioned area of corpus callosum and stopping close to the areas found active in fMRI. The behavioral disconnection syndrome could, thus, be related functionally to abnormal fMRI activations and anatomically to the absence of a connection between those activations. The present approach, based on the "negative tracking" of degenerated bundles, provides new perspectives on the understanding of human brain connections and disconnections

Dehaene, S., Naccache, L., Cohen, L., Bihan, D. L., Mangin, J. F., Poline, J. B. et al. (2001). Cerebral mechanisms of word masking and unconscious repetition priming. Nature Neuroscience, 4, 752-758.
Notes: Unite INSERM 334, IFR 49, Service Hospitalier Frederic Joliot, CEA/DSV, 4 Place du General Leclerc, 91401 Orsay cedex, France.
We used functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) to visualize the cerebral processing of unseen masked words. Within the areas associated with conscious reading, masked words activated left extrastriate, fusiform and precentral areas. Furthermore, masked words reduced the amount of activation evoked by a subsequent conscious presentation of the same word. In the left fusiform gyrus, this repetition suppression phenomenon was independent of whether the prime and target shared the same case, indicating that case-independent information about letter strings was extracted unconsciously. In comparison to an unmasked situation, however, the activation evoked by masked words was drastically reduced and was undetectable in prefrontal and parietal areas, correlating with participants' inability to report the masked words

Cohen, L. & Dehaene, S. (2000). Calculating without reading: Unsuspected residual abilities in pure alexia. Cognitive Neuropsychology, 17, 563-583.
Notes: L. Cohen, Service de Neurologie 1, Clinique Paul Castaigne, Hopital de la Salpetriere, 47/83 Bd de l'Hopital, 75651 Paris Cedex 13, France ; ABSTRACT: In pure alexic patients, clear-cut dissociations between impaired naming and preserved comprehension abilities can be found in the domain of number processing (Cohen and Dehaene, 1995). In the present study, we report a novel case of pure alexia with striking preservation of some calculation abilities. The patient was fully able to decide which of two numbers was the larger, or whether a number was odd or even, even with 2-digit numerals for which she made close to 90% reading errors. In arithmetic the patient, though unable to read aloud correctly the operands of visually presented problems, could still produce verbally the exact result of the very same problems. For instance, when presented visually with the subtraction problem 8 - 6, the patient read the problem aloud as 'five minus four', but nevertheless produced the correct result 'two.' Such capacities for 'calculating without reading' were observed in subtraction, addition, and division tasks, but not in multiplication tasks. We discuss how both the existence of residual abilities and the pattern of dissociations between operation types can be explained by current theories of the cerebral substrates of number processing (Dehaene and Cohen, 1995)

Cohen, L., Dehaene, S., Naccache, L., Lehericy, S., Dehaene Lambertz, G., Henaff, M. A. et al. (2000). The visual word form area: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients. Brain, 123, 291-307.
Notes: Service de Neurologie 1, INSERM U334, Service Hospitalier Frederic Joliot, CEA/DSV, Orsay, France. laurent.cohen@psl.ap-hop- ; ABSTRACT: A standard model of word reading postulates that visual information is initially processed by occipitotemporal areas contralateral to the stimulated hemifield, from whence it is subsequently transferred to the visual word form (VWF) system, a left inferior temporal region specifically devoted to the processing of letter strings. For stimuli displayed in the left visual field, this transfer proceeds from the right to the left hemisphere through the posterior portion of the corpus callosum. In order to characterize the spatial and temporal organization of these processes, reading tasks with split-field presentation were performed by five control subjects and by two patients suffering from left hemialexia following posterior callosal lesions. The subjects' responses were studied using behavioural measures and functional brain imaging techniques, providing both high spatial resolution (functional MRI, fMRI) and high temporal resolution (high-density event- related potentials, ERPs). Early visual processing was revealed as activations contralateral to stimulation, located by fMRI in the inferior occipitotemporal region and presumably coincident with area V4. A negative wave occurring 150-160 ms post-stimulus, also strictly contralateral to stimulation, was recorded over posterior electrodes. In contrast with these hemifield-dependent effects, the VWF system was revealed as a strictly left- hemispheric activation which, in control subjects, was identical for stimuli presented in the left or in the right hemifield and was located in the middle portion of the left fusiform gyrus. The electrical signature of the VWF system consisted of a unilateral sharp negativity, recorded 180- 200 ms post-stimulus over left inferior temporal electrodes. In callosal patients, due to the inability of visual information to pass across the posterior part of the corpus callosum, the VWF system was activated only by stimuli presented in the right visual field. Similarly, a significant influence of the word/non- word status on ERPs recorded over the left hemisphere was discernible for either hemifield in controls, while it affected only right-hemifield stimuli in callosal patients. These findings provide direct support for the main components of the classical model of reading and help specify their timing and cerebral substrates

Cohen, L. & Dehaene, S. (1995). Number processing in pure alexia: The effect of hemispheric asymmetries and task demands. Neurocase, 1, 121-137.

Anders Gade