En cherchant des références sur l’aphasie optique , je suis tombé sur ce pdf qui fournit une bibliographie importante sur l’alexie pure (ou «alexie lettre par lettre», ou «alexie littérale»). Les références et abstracts que vous y trouverez ne dépassent pas l’année 2000. Il m’a cependant paru utile de vous le signaler.
Il s’agit d’une présentation faite dans la revue « Neurocase » par Marie Montant et Marlene Behrmann – Neurocase, 2000, 6, 265-294.
Vous trouverez aussi ci-dessous d’autres liens vers des articles complets sur ce sujet. Mais je ne prétends pas à l’exhaustivité et vous pouvez ajouter des commentaires avec d’autres liens.
Rapid Word Identification in Pure Alexia Is Lexical but Not Semantic
Rhonda B. Friedman and Susan Nitzberg Lott
Brain and Language 72, 219–237 (2000)
Following the notion that patients with pure alexia have access to two distinct reading strategies — letter-by-letter reading and semantic reading — a training program was devised to facilitate reading via semantics in a patient with pure alexia.
Training utilized brief stimulus presentations and required category judgments rather than explicit word identification. The training was successful for trained words, but generalized poorly to untrained words. Additional studies involving oral reading of nouns and of functors also resulted in improved reading of trained words.
Pseudowords could not be trained to criterion. The results suggest that improved reading can be achieved in pure alexia by pairing rapidly presented words with feedback. Focusing on semantic processing is not essential to this process. It is proposed that the training strengthens connections between the output of visual processing and preexisting orthographic representations.
Can Treatment for Pure Alexia Improve Letter-by-Letter Reading Speed without Sacrificing Accuracy?
Susan Nitzberg Lott and Rhonda B. Friedman
Brain and Language 67, 188–201 (1999)
An experimental treatment study designed to improve both the accuracy and the speed of reading was administered to a patient with pure alexia and impaired letter naming. The study focused on the use of letter-by-letter reading. A two-stage approach was employed. The first stage implemented a tactile–kinesthetic strategy to improve accuracy. The second stage concentrated on speed. At the end of the treatment, patient DL was reading both trained and untrained words more accurately and with considerably greater speed than prior to treatment. Accuracy and speed of reading at the sentence level improved as well.
VARIETIES OF PURE ALEXIA: THE CASE OF FAILURE TO ACCESS GRAPHEMIC REPRESENTATIONS
Michele Miozzo and Alfonso Caramazza
COGNITIVE NEUROPSYCHOLOGY, 1998, 15 (1/2), 203- 238
We document the case of a patient (GV) who, following a left posterior brain lesion, showed a selective and severe deficit in naming visual objects and in reading letters, words, and numerals. Three sets of findings are critical for the interpretation of the patient’s alexia. First, despite intact visual processing abilities and preserved ability to recognise the shape and orientation of letters, GV could not determine whether a pair of letters had the same name.
Second, she should not access the orthographic structure and meaning of visually presented words, although she could access meaning from orally spelled words and she could access orthographic structure from meaning in written words. Third , GV could access partial semantic information from pictures and Arabic numerals. Based on this pattern of results, we conclude that the form of alexia manifested by our patient results from failure to access the graphemic representations of letters and words from normally processed visual input. The findings further suggest that access to letter forms and grapheme representations are sequentially ordered stages of processing in word recognition. The results also suggest that graphemic processing may be a distinct property of the left hemisphere.
Calculating without reading: Unsuspected residual abilities in pure alexia
Laurent Cohen and Stanislas Dehaene
COGNITIVE NEUROPSYCHOLOGY,Volume 17, Number 6, 1 September 2000, pp. 563-583
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 two-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).
Voir aussi :
OCCAM’S RAZOR IS NOT A SWISS-ARMY KNIFE: A REPLY TO PILLON AND PESENTI
Laurent Cohen and Stanislas Dehaene
COGNITIVE NEUROPSYCHOLOGY, 2001, 18 (3), 285–288
Our paper reported a dissociation, in a pure alexic patient, between impaired reading and multiplication of Arabic digits on the one hand, and relatively preserved comparison, subtraction, addition, and simple division on the other hand (Cohen & Dehaene, 2000). We showed how the main features of this puzzling case can be explained by the triple-code model of number processing (Dehaene & Cohen, 1995; Dehaene, Dehaene-Lambertz, & Cohen, 1998). (As a matter of historical fact, the model was actually used to predict this dissociation and to actively look for it in our sample of patients.) This case also confirmed a previous description of two other pure alexic patients with preserved number comparison in the face of grossly impaired reading (Cohen & Dehaene, 1995), and closely related observations in a split-brain patient (Cohen & Dehaene, 1996). Similar findings have been reported by others (Gazzaniga & Smylie, 1984; McNeil & Warrington, 1994; Miozzo & Caramazza, 1998; Seymour, Reuter-Lore
nz, & Gazzaniga, 1994).
Although Pillon and Pesenti (2001, this issue; henceforth P&P) dismiss our evidence as not even constraining theories of numerical cognition, they struggle to find an alternative theory compatible with the facts. Starting with the postulate that there must be alternative accounts of our data, they bring forward a paraphernalia of theoretical constructs that are specifically tailored, one by one, to fit our empirical data (in their words, they are “[not] claiming that it could account for a larger range of observations than just this study”; this issue, p. 283). In the end, they reach what they claim is a viable alternative with “three functional components.”
Numbers being the issue, it is interesting to observe that their Figure 1 actually reveals a total of 6 main boxes, some comprising up to 6 sub-components, linked by no less than 13 arrows. To keep this reply short, we shall not dwell here on the avowed lack of “fine specification” of P&P’s model. Rather, we briefly show why the explanations that they sketch for the dissociations observed in patient VOL do not work.
Mechanisms of pure alexia: spatially-based impairment, letter identification deficit, or both?
Anne-Catherine Bachoud-Lévi, Paolo Bartolomeo
Neurocase, in press (2002)
We studied reading performance for words and for isolated letters in a pure alexic patient. She performed reasonably well when naming isolated letters but was slower in reading letters than a control subject when reaction times (RTs) were recorded. When the patient read isolated letters, RTs were slower for a subset of letters that cannot be recognized from their left part alone (e.g. “b”, an ambiguous letter, could be read « b » « h » « l » or « k » whereas « a » has no predictable confounders). We observed a significant positive correlation between the RTs for reading a word and the mean RTs for reading each of its composing letter before its uniqueness point (i.e. the point, when reading from the left to the right, where a word cannot be a word other than the one it is). This result suggests that, in our patient, the letter identification deficit can account for the slow, letter-by-letter reading behaviour, insofar as each letter represents a perceptual problem. Our findings can be accounted for by a deficit in the parallel processing of the left and right parts of each letter, compounded with a bias to process first the left part of the letter, and may thus reconcile the hypotheses of spatially-based deficit (Rapp and Caramazza, 1991) and of a perceptual deficit occurring at the letter identification level (Behrmann & Shallice, 1995; Perri, Bartolomeo and Silveri, 1996).
PHONOLOGICAL ACTIVATION IN PURE ALEXIA
Marie Montant and Marlene Behrmann
COGNITIVE NEUROPSYCHOLOGY, 2001, 18 (8), 697–727
Pure alexia is a reading impairment in which patients appear to read letter-by-letter. This disorder is typically accounted for in terms of a peripheral deficit that occurs early on in the reading system, prior to the activation of orthographic word representations. The peripheral interpretation of pure alexia has recently been challenged by the phonological deficit hypothesis, which claims that a postlexical disconnection between orthographic and phonological information contributes to or is responsible for the disorder.
Because this hypothesis was mainly supported by data from a single patient (IH), who also has surface dyslexia, the present study re-examined this hypothesiswith another pure alexic patient (EL). In contrast to patient IH, EL did not show any evidence of a phonological deficit. Her pattern of performance in naming was not qualitatively different fromthat of normal readers; she appeared to be reading via a mode of processing resulting in strong serial and lexical effects, a pattern often observed in normal individuals reading unfamiliar stimuli. The present results do not obviously support the phonological hypothesis and are more consistent with peripheral interpretations of pure alexia. The peripheral and the phonological accounts of pure alexia are discussed in light of two current models of visual word recognition.
Neuropsychologie et imagerie de la lecture
Nous proposons un modèle anatomique et fonctionnel simple des étapes visuelles de la lecture, modèle qui permet de rendre compte d’un large éventail de données comportementales, neuropsychologiques et d’imagerie fonctionnelle cérébrale. Ce thème permettra d’illustrer la conjonction de méthodes comportementales et de techniques d’imagerie anatomique et fonctionnelle, pour l’étude de patients souffrant de lésions cérébrales.
Les mécanismes cérébraux de la lecture : un modèle en neurologie cognitive
Michel Habib et Fabrice Robichon
médecine/sciences 1996 ; 12 : 707-14 m/s n° 6-7, vol. 12, juin-juillet 96
L’étude anatomo-clinique des alexies, pertes de la lecture consécutives à des lésions focales du cerveau, a donné naissance aux conceptions classiques de déconnexion inter- ou intrahémisphérique des syndromes neuropsychologiques. La révolution cognitiviste, au cours des vingt dernières années, également fondée sur les dissociations observées lors de perturbations acquises de la lecture, a permis de distinguer les dyslexies profondes (phonologiques) des dyslexies de surface (lexico-sémantiques). Actuellement, les méthodes d’imagerie fonctionnelle du cerveau appliquées à la lecture laissent entrevoir un rapprochement des conceptions anatomo-clinique et cognitiviste. Enfin, l’étude du développement s’impose de plus en plus pour préciser les fonctions cognitives. C’est dans le domaine de la lecture, avec les dyslexies liées au développement, que se réalisent actuellement les premiers travaux permettant de mettre en relation des déficits de processus cognitifs précis avec la mise en place défectueuse de certains circuits cérébraux.
Structural anatomy of pure and hemianopic alexia
A P Leff, G Spitsyna, G T Plant and R J S Wise
J. Neurol. Neurosurg. Psychiatry published online 26 Jun 2006
The two commonest types of acquired reading disorder resulting from damage to the territory of the dominant posterior cerebral artery are hemianopic and pure alexia. Patients with pronounced hemianopic alexia have a right homonymous hemianopia that encroaches into central/parafoveal vision; they read individual words well, but generate inefficient reading saccades when reading along a line of text. Patients with pure alexia also often have a hemianopia but are more disabled, making frequent errors on individual words; they have sustained damage to a brain region that supports efficient word identification.
Objectives: To investigate the differences in lesion site between these two groups, as rehabilitative techniques differ between the two conditions.
Methods: High-resolution MRI scans were obtained from seven patients w
ith hemianopic alexia and six patients with pure alexia caused by a left occipital stroke. The boundary of each lesion was defined and lesion volumes were then transformed into a standard stereotactic space so that regional comparisons could be made.
Results: The two patient groups did not differ in terms of damage to the medial left occipital lobe, but those with pure alexia had additional lateral damage to the posterior fusiform gyrus and adjacent tissue.
Conclusions: Clinicians will be able to predict the type of reading disorder patients with left occipital lesions have from simple tests of reading speed and the distribution of damage to the left occipital lobe on brain imaging. This information will aid management decisions including recommendations for reading rehabilitation.
The visual word form area: expertise for reading in the fusiform gyrus
Bruce D. McCandliss, Laurent Cohen and Stanislas Dehaene
TRENDS in Cognitive Sciences Vol.7 No.7 July 2003
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.
Disruption of residual reading capacity in a pure alexic patient after a mirror-image right-hemispheric lesion.
Paolo Bartolomeo, Anne-Catherine Bachoud-Lévi, Jean-Denis Degos, and François Boller
A 74-year-old woman became a letter-by-letter reader after the occurrence of a left occipito-temporal hematoma. Seven months later, she suffered a second, mirror-image hematoma in the right hemisphere. After this second lesion, her residual reading capacity deteriorated dramatically in terms of both accuracy and reading latencies for words and isolated letters. Our findings support the hypothesis that the right hemisphere contributes to the residual reading capacities of pure alexic patients.
Impaired reading in patients with right hemianopia.
Leff AP, Scott SK, Crewes H, Hodgson TL, Cowey A, Howard D, Wise RJS.
Ann Neurol 2000;47:171–178
A left occipital stroke may result in alexia for two reasons, which may coexist depending on the distribution of the lesion. A lesion of the left lateroventral prestriate cortex or its afferents impairs word recognition (“pure” alexia). If the left primary visual cortex or its afferents are destroyed, resulting in a complete right homonymous hemianopia, rightward saccades during text reading are disrupted (“hemianopic” alexia). By using functional imaging, we showed two separate but interdependent systems involved in reading. The first, subserving word recognition, involved the representation of foveal vision in the left and right primary visual cortex and the ventral prestriate cortex.
The second system, responsible for the planning and execution of reading saccades, consisted of the representation of right parafoveal vision in the left visual cortex, the bilateral posterior parietal cortex (left > right), and the frontal eye fields (right > left). Disruption of this distributed neural system was demonstrated in patients with severe right homonymous hemianopia, commensurate with their inability to perform normal reading eye movements. Text reading, before processes involved in comprehension, requires the integration of perceptual and motor processes. We have demonstrated these distributed neural systems in normal readers and have shown how a right homonymous hemianopia disrupts the motor preparation of reading saccades during text reading.
Brain activations during letter-by-letter reading: A follow-up study
Carole Henry, Raphaël Gaillard, Emmanuelle Volle, Jacques Chiras, Sophie Ferrieux, Stanislas Dehaene, Laurent Cohen
Neuropsychologia xxx (2005) xxx–xxx
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., Leh´ericy, S., Martinaud, O., Lemer, C., & 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.
The eye movements of pure alexic patients during reading and nonreading tasks
M. Behrmann, S.S. Shomstein, S.E. Black, J.J.S. Barton
Neuropsychologia 39 (2001) 983–1002
We compared the eye-movements of two patients who read letter-by-letter (LBL) following a left occipital lobe lesion with those of normal control subjects and of hemianopic patients in two tasks: a nonreading visual search task and a text reading task. Whereas the LBL readers exhibited similar eye-movement patterns to those of the other two groups on the nonreading task, their eye movements differed significantly during reading, as reflected in the disproportionate increase in th
e number and duration of fixations per word and in the regressive saccades per word. Importantly, relative to the two control groups, letter-by-letter readers also made more fixations per word as word length increased, especially as word frequency and word imageability decreased. Two critical results emerged from these experiments: First, the alteration in the oculomotor behavior of the LBL readers during reading is similar to that seen in normal readers under difficult reading conditions, as well as in beginning readers and in those with developmental dyslexia, and appears to reflect difficulties in processing the visual stimulus. Second, the interaction of length with frequency and with imageability in determining the eye movement pattern is consistent with an interactive activation model of normal word recognition in which weakened activation of orthographic input can nevertheless engage high-level lexical factors.
PERCEPTUAL AND LEXICAL FACTORS IN A CASE OF LETTER-BY-LETTER READING
Doriana Chialant and Alfonso Caramazza
COGNITIVE NEUROPSYCHOLOGY, 1998, 15 (1/2), 167- 201
We report the case of a letter-by-letter reader (MJ) who showed normal processing of single letters and who could normally access the orthographic input lexicon when presented with letter names for aural recognition, or when allowed enough time to process a visually presented letter string . However, MJ showed severe difficulties in simultaneously processing multiple letters and other simple visual stimuli. Furthermore, she does not have normal access to lexical orthographic representations and their meanings when stimuli are presented for too brief a time to allow for serial processing of the letter string . We found no evidence of (partial) lexical or semantic access without corresponding recognition of the letters in a word: No signs of implicit reading were observed when the input stimuli were controlled for the relevant visual features; “implicit reading” was only obtained under conditions that allowed sophisticated guessing . This pattern of results is interpreted as indicating that LBL reading (at least in MJ) results from damage to prelexical processing mechanisms.
In MJ’s case, the deficit reflects the degraded transfer of information from a normal visual processing system in the right hemisphere to a normal language processing system in the left hemisphere.