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Alexander P. Leff - One of the best experts on this subject based on the ideXlab platform.
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Reading therapy strengthens top–down connectivity in patients with Pure Alexia
Brain, 2013Co-Authors: Zoe Woodhead, Hilary Crewes, William D. Penny, Gareth R. Barnes, Richard Wise, Cathy J. Price, Alexander P. LeffAbstract:This study tested the efficacy of audio-visual reading training in nine patients with Pure Alexia, an acquired reading disorder caused by damage to the left ventral occipitotemporal cortex. As well as testing the therapy’s impact on reading speed, we investigated the functional reorganization underlying therapy-induced behavioural changes using magnetoencephalography. Reading ability was tested twice before training (t1 and t2) and twice after completion of the 6-week training period (t3 and t4). At t3 there was a significant improvement in word reading speed and reduction of the word length effect for trained words only. Magnetoencephalography at t3 demonstrated significant differences in reading network connectivity for trained and untrained words. The training effects were supported by increased bidirectional connectivity between the left occipital and ventral occipitotemporal perilesional cortex, and increased feedback connectivity from the left inferior frontal gyrus. Conversely, connection strengths between right hemisphere regions became weaker after training.
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Word-superiority in Pure Alexia
Behavioural Neurology, 2013Co-Authors: Randi Starrfelt, Christian Gerlach, Thomas Habekost, Alexander P. LeffAbstract:Pure Alexia is an acquired reading disorder where patients lose the ability to read fast and fluently, but are commonly able to identify words letter-by-letter. This is evidenced by a pronounced word-length effect in reading, where reaction times (RTs) increase linearly with word length. The severity of the reading deficit in Pure Alexia has been reported to be systematically related to performanceon lexical and semantic decision tasks [1] and to visuoperceptual deficits [2]. Lesions to the suggested ‘visual word form area’ (VWFA) located in the left mid-fusiform gyrus seem to be of particular importance in causing Pure Alexia [3,4]. In the current study, we examine the word superiority effect (WSE) in four Pure alexic patients. The WSE refers to the phenomenon that normal readers are better at identifying letters embedded in words than in letter strings [5]. The effect is typically found in experiments where stimuli are presented briefly and then masked, followed by either a forced choice or free report task. There are a few case studies of the word-superiority effect in Pure Alexia (e.g. [6]) but findings so far have been contradictory. There have been no systematic attempts at linking performance in WSE experiments to visuoperceptual abilities or severity in Pure Alexia.
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Reading therapy strengthens top-down connectivity in patients with Pure Alexia.
Brain : a journal of neurology, 2013Co-Authors: Zoe Woodhead, Hilary Crewes, Gareth R. Barnes, Cathy J. Price, William Penny, Richard J S Wise, Alexander P. LeffAbstract:This study tested the efficacy of audio-visual reading training in nine patients with Pure Alexia, an acquired reading disorder caused by damage to the left ventral occipitotemporal cortex. As well as testing the therapy's impact on reading speed, we investigated the functional reorganization underlying therapy-induced behavioural changes using magnetoencephalography. Reading ability was tested twice before training (t1 and t2) and twice after completion of the 6-week training period (t3 and t4). At t3 there was a significant improvement in word reading speed and reduction of the word length effect for trained words only. Magnetoencephalography at t3 demonstrated significant differences in reading network connectivity for trained and untrained words. The training effects were supported by increased bidirectional connectivity between the left occipital and ventral occipitotemporal perilesional cortex, and increased feedback connectivity from the left inferior frontal gyrus. Conversely, connection strengths between right hemisphere regions became weaker after training.
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Too Little, Too Late: Reduced Visual Span and Speed Characterize Pure Alexia
Cerebral Cortex, 2009Co-Authors: Randi Starrfelt, Thomas Habekost, Alexander P. LeffAbstract:Whether normal word reading includes a stage of visual processing selectively dedicated to word or letter recognition is highly debated. Characterizing Pure Alexia, a seemingly selective disorder of reading, has been central to this debate. Two main theories claim either that 1) Pure Alexia is caused by damage to a reading specific brain region in the left fusiform gyrus or 2) Pure Alexia results from a general visual impairment that may particularly affect simultaneous processing of multiple items. We tested these competing theories in 4 patients with Pure Alexia using sensitive psychophysical measures and mathematical modeling. Recognition of single letters and digits in the central visual field was impaired in all patients. Visual apprehension span was also reduced for both letters and digits in all patients. The only cortical region lesioned across all 4 patients was the left fusiform gyrus, indicating that this region subserves a function broader than letter or word identification. We suggest that a seemingly Pure disorder of reading can arise due to a general reduction of visual speed and span, and explain why this has a disproportionate impact on word reading while recognition of other visual stimuli are less obviously affected.
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The functional anatomy of single-word reading in patients with hemianopic and Pure Alexia.
Brain, 2001Co-Authors: Alexander P. Leff, Hilary Crewes, Gordon T. Plant, Sophie K. Scott, C. Kennard, R.j.s. WiseAbstract:We investigated single-word reading in normal subjects and patients with Alexia following a left occipital infarct, using PET. The most posterior brain region to show a lateralized response was at the left occipitotemporal junction, in the inferior temporal gyrus. This region was activated when normal subjects, patients with hemianopic Alexia and patients with an incomplete right homonymous hemianopia, but no reading deficit, viewed single words presented at increasing rates. This same area was damaged in a patient with Pure Alexia ("Alexia without agraphia") and no hemianopia, who read words slowly using a letter-by-letter strategy. Although the exact level of the functional deficit is controversial, Pure Alexia is the result of an inability to map a percept of all the letters in a familiar letter string on to the mental representation of the whole word form. However, the commonest deficit associated with "Pure" Alexia is a right homonymous field defect; an impairment that may, by itself, interfere with single-word reading because of inability to see the letters towards the end of a word. The relative contributions of Pure and hemianopic Alexia in individual patients needs to be assessed, as the latter has been shown to respond well to specific rehabilitation programmes.
Randi Starrfelt - One of the best experts on this subject based on the ideXlab platform.
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Pure Alexia: A Combined First-Person Account and Neuropsychological Investigation.
Cognitive and Behavioral Neurology, 2019Co-Authors: Klaus Hansen, Randi StarrfeltAbstract:Pure Alexia is an acquired reading disorder where patients' ability to read words and text is severely impaired, while their writing is left unaffected. Patients with Pure Alexia typically recover some reading ability over time, although most never regain their premorbid reading skills. A few studies have reported some behavioral and imaging correlates of such remission; however, little is known about the patients' experience of their reading impairment. This paper contains a first-person account of Pure Alexia, describing the first author's (K.H.) experience of his remission from severe reading problems immediately following a posterior cerebral artery stroke to the mild Pure Alexia characterizing his reading ability today. To provide a context for this account, we also present neuropsychological and reading data obtained from K.H. at several time points during his recovery.
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Number reading in Pure Alexia — A review
2018Co-Authors: Randi Starrfelt, Marlene BehrmannAbstract:It is commonly assumed that number reading can be intact in patients with Pure Alexia, and that this dissociation between letter/word recognition and number reading strongly constrains theories of visual word processing. A truly selective deficit in letter/word processing would strongly support the hypothesis that there is a specialized system or area dedicated to the processing of written words. To date, however, there has not been a systematic review of studies investigating number reading in Pure Alexia and so the status of this assumed dissociation is unclear. We review the literature on Pure Alexia from 1892 to 2010, and find no well-documented classical dissociation between intact number reading and impaired letter identification in a patient with Pure Alexia. A few studies report strong dissociations, with number reading less impaired than letter reading, but when we apply rigorous statistical criteria to evaluate these dissociations, the difference in performance across domains is not statistically significant. There is a trend in many cases of Pure Alexia, however, for number reading to be less affected than letter identification and word reading. We shed new light on this asymmetry by showing that, under conditions of brief exposure, normal participants are also better at identifying digits than letters. We suggest that the difference observed in some Pure alexic patients may possibly reflect an amplification of this normal difference in the processing of letters and digits, and we relate this asymmetry to intrinsic differences between the two types of symbols.
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What's in a name? The characterization of Pure Alexia
Cognitive Neuropsychology, 2014Co-Authors: Randi Starrfelt, Tim ShalliceAbstract:Pure Alexia is a selective impairment of reading in the absence of other language de ficits and occurs as a consequence of brain injury in previously literate individuals. The syndrome has intrigued researchers for well over a century and is the most studied of the acquired reading disorders. Pure Alexia has been extensively investigated over the last 40 years within the framework of cognitive neuropsychology, but the syndrome, as a clinical entity, much predates the inferential methodology ofcognitiveneuropsychology.Itisbasedonempirical generalizations by clinicians of a counterintuitive and relatively infrequent but, nonetheless, consistently observed set of behaviours in patients. However, different sets of critical features have been proposed to de fine the disorder. This is indicated by the range of names with similar but not identical referents with which the syndrome has been labelled over the last 120 years, e.g., Alexia without agraphia, agnosic Alexia, word form dyslexia, verbal Alexia, global Alexia, word blindness, letter-byletter (LBL) reading, letter-by-letter dyslexia, and spelling dyslexia . Some labels indicate degree of severity (global alexic patients are totally unable to read even single letters) while others focus on the compensa
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From word superiority to word inferiority: Visual processing of letters and words in Pure Alexia
Cognitive Neuropsychology, 2014Co-Authors: Thomas Habekost, Marlene Behrmann, Anders Petersen, Randi StarrfeltAbstract:Visual processing and naming of individual letters and short words were investigated in four patients with Pure Alexia. To test processing at different levels, the same stimuli were studied across a naming task and a visual perception task. The normal word superiority effect was eliminated in both tasks for all patients, and this pattern was more pronounced in the more severely affected patients. The relationship between performance with single letters and words was, however, not straightforward: One patient performed within the normal range on the letter perception task, while being severely impaired in letter naming and word processing, and performance with letters and words was dissociated in all four patients, with word reading being more severely impaired than letter recognition. This suggests that the word reading deficit in Pure Alexia may not be reduced to an impairment in single letter perception.
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Rehabilitation of Pure Alexia: A review
Neuropsychological Rehabilitation, 2013Co-Authors: Randi Starrfelt, Rannveig Rós Ólafsdóttir, Ida-marie ArendtAbstract:Acquired reading problems caused by brain injury (Alexia) are common, either as a part of an aphasic syndrome, or as an isolated symptom. In Pure Alexia, reading is impaired while other language functions, including writing, are spared. Being in many ways a simple syndrome, one would think that Pure Alexia was an easy target for rehabilitation efforts. We review the literature on rehabilitation of Pure Alexia from 1990 to the present, and find that patients differ widely on several dimensions, such as Alexia severity and associated deficits. Many patients reported to have Pure Alexia in the reviewed studies, have associated deficits such as agraphia or aphasia and thus do not strictly conform to the diagnosis. Few studies report clear and generalisable effects of training, none report control data, and in many cases the reported findings are not supported by statistics. We can, however, tentatively conclude that Multiple Oral Re-reading techniques may have some effect in mild Pure Alexia where diminished reading speed is the main problem, while Tacile-Kinesthetic training may improve letter identification in more severe cases of Alexia. There is, however, still a great need for well-designed and controlled studies of rehabilitation of Pure Alexia.
Marlene Behrmann - One of the best experts on this subject based on the ideXlab platform.
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Pure Alexia
2018Co-Authors: Marie Montant, Marlene BehrmannAbstract:Pure Alexia is a reading disorder that occurs in literate individuals secondary to a lesion in the left occipito-temporal region.
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Number reading in Pure Alexia — A review
2018Co-Authors: Randi Starrfelt, Marlene BehrmannAbstract:It is commonly assumed that number reading can be intact in patients with Pure Alexia, and that this dissociation between letter/word recognition and number reading strongly constrains theories of visual word processing. A truly selective deficit in letter/word processing would strongly support the hypothesis that there is a specialized system or area dedicated to the processing of written words. To date, however, there has not been a systematic review of studies investigating number reading in Pure Alexia and so the status of this assumed dissociation is unclear. We review the literature on Pure Alexia from 1892 to 2010, and find no well-documented classical dissociation between intact number reading and impaired letter identification in a patient with Pure Alexia. A few studies report strong dissociations, with number reading less impaired than letter reading, but when we apply rigorous statistical criteria to evaluate these dissociations, the difference in performance across domains is not statistically significant. There is a trend in many cases of Pure Alexia, however, for number reading to be less affected than letter identification and word reading. We shed new light on this asymmetry by showing that, under conditions of brief exposure, normal participants are also better at identifying digits than letters. We suggest that the difference observed in some Pure alexic patients may possibly reflect an amplification of this normal difference in the processing of letters and digits, and we relate this asymmetry to intrinsic differences between the two types of symbols.
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Perceptual Cues in Pure Alexia
2018Co-Authors: Erica B. Sekuler, Marlene BehrmannAbstract:This study provides evidence that Pure Alexia, or letter-by-letter reading, may be attributed to a general perceptual deficit that extends beyond an orthographic disorder. The perceptual problem may be unmasked when appropriate perceptual cues are not available to aid in the derivation of an integrated structural description. Four Pure alexic patients and eight nonbrain-damaged controls participated in this study. In the first two experiments, subjects’ reading abilities were assessed on a naming latency and a lexical decision task. Experiment 3 replicated Farah and Wallace’s (1991) results that the Pure Alexia deficit was not specific to orthography. Experiments 4 and 5 further explored the nature of the perceptual disorder using nonorthographic stimuli. In Experiment 4, patient performance on a target detection task was unaOEected by the number of parts comprising the object but was impaired when the perceptual cue of good continuation was absent. Patient performance also declined when the perceptual cue of symmetry was not available to aid in the integration of occluded object parts in Experiment 5. Overall, the results imply that Pure Alexia is most likely to arise from a more general, nonorthographic deficit, and that the nature of the disorder is revealed when the perceptual context lacks strong perceptual cues
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From word superiority to word inferiority: Visual processing of letters and words in Pure Alexia
Cognitive Neuropsychology, 2014Co-Authors: Thomas Habekost, Marlene Behrmann, Anders Petersen, Randi StarrfeltAbstract:Visual processing and naming of individual letters and short words were investigated in four patients with Pure Alexia. To test processing at different levels, the same stimuli were studied across a naming task and a visual perception task. The normal word superiority effect was eliminated in both tasks for all patients, and this pattern was more pronounced in the more severely affected patients. The relationship between performance with single letters and words was, however, not straightforward: One patient performed within the normal range on the letter perception task, while being severely impaired in letter naming and word processing, and performance with letters and words was dissociated in all four patients, with word reading being more severely impaired than letter recognition. This suggests that the word reading deficit in Pure Alexia may not be reduced to an impairment in single letter perception.
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Number reading in Pure Alexia--a review.
Neuropsychologia, 2011Co-Authors: Randi Starrfelt, Marlene BehrmannAbstract:a b s t r a c t It is commonly assumed that number reading can be intact in patients with Pure Alexia, and that this dissociation between letter/word recognition and number reading strongly constrains theories of visual word processing. A truly selective deficit in letter/word processing would strongly support the hypothesis that there is a specialized system or area dedicated to the processing of written words. To date, however, there has not been a systematic review of studies investigating number reading in Pure Alexia and so the status of this assumed dissociation is unclear. We review the literature on Pure Alexia from 1892 to 2010, and find no well-documented classical dissociation between intact number reading and impaired letter identification in a patient with Pure Alexia. A few studies report strong dissociations, with number reading less impaired than letter reading, but when we apply rigorous statistical criteria to evaluate these dissociations, the difference in performance across domains is not statistically significant. There is a trend in many cases of Pure Alexia, however, for number reading to be less affected than letter identification and word reading. We shed new light on this asymmetry by showing that, under conditions of brief exposure, normal participants are also better at identifying digits than letters. We suggest that the difference observed in some Pure alexic patients may possibly reflect an amplification of this normal difference in the processing of letters and digits, and we relate this asymmetry to intrinsic differences between the two types of symbols.
Stanislas Dehaene - One of the best experts on this subject based on the ideXlab platform.
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Brain mechanisms of recovery from Pure Alexia : a single case study with multiple longitudinal scans
Neuropsychologia, 2016Co-Authors: Laurent D. Cohen, Stanislas Dehaene, Samantha F. Mccormick, Szonya Durant, Johannes M. ZankerAbstract:Pure Alexia is an acquired reading disorder, typically due to a left occipito-temporal lesion affecting the Visual Word Form Area (VWFA). It is unclear whether the VWFA acts as a unique bottleneck for reading, or whether alternative routes are available for recovery. Here, we address this issue through the single-case longitudinal study of a neuroscientist who experienced Pure Alexia and participated in 17 behavioral, 9 anatomical, and 9 fMRI assessment sessions over a period of two years. The origin of the impairment was assigned to a small left fusiform lesion, accompanied by a loss of VWFA responsivity and by the degeneracy of the associated white matter pathways. fMRI experiments allowed us to image longitudinally the visual perception of words, as compared to other classes of stimuli, as well as the mechanisms of letter-by-letter reading. The progressive improvement of reading was not associated with the re-emergence of a new area selective to words, but with increasing responses in spared occipital cortex posterior to the lesion and in contralateral right occipital cortex. Those regions showed a non-specific increase of activations over time and an increase in functional correlation with distant language areas. Those results confirm the existence of an alternative occipital route for reading, bypassing the VWFA, but they also point to its key limitation: the patient remained a slow letter-by-letter reader, thus supporting the critical importance of the VWFA for the efficient parallel recognition of written words.
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Pure Alexia as a disconnection syndrome new diffusion imaging evidence for an old concept
Cortex, 2008Co-Authors: Stephane Epelbaum, Philippe Pinel, Raphael Gaillard, Christine Delmaire, Muriel Perrin, Sophie Dupont, Stanislas DehaeneAbstract: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.
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Calculating without reading: unsuspected residual abilities in Pure Alexia.
Cognitive Neuropsychology, 2000Co-Authors: Laurent Cohen, Stanislas DehaeneAbstract:In Pure alexic patients, clear-cut dissociations between impaired naming and preserved comprehension abilities can be found in the domain of number processing (Cohen & 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...
Thomas Habekost - One of the best experts on this subject based on the ideXlab platform.
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Advance Access publication April 14, 2009 Too Little, Too Late: Reduced Visual Span and Speed Characterize Pure Alexia
2015Co-Authors: I Starrfelt, Thomas Habekost, Er P. LeffAbstract:Whether normal word reading includes a stage of visual processing selectively dedicated to word or letter recognition is highly debated. Characterizing Pure Alexia, a seemingly selective disorder of reading, has been central to this debate. Two main theories claim either that 1) Pure Alexia is caused by damage to a reading specific brain region in the left fusiform gyrus or 2) Pure Alexia results from a general visual impairment that may particularly affect simultaneous process-ing of multiple items. We tested these competing theories in 4 patients with Pure Alexia using sensitive psychophysical measures and mathematical modeling. Recognition of single letters and digits in the central visual field was impaired in all patients. Visual apprehension span was also reduced for both letters and digits in all patients. The only cortical region lesioned across all 4 patients was the left fusiform gyrus, indicating that this region subserves a function broader than letter or word identification. We suggest that a seemingly Pure disorder of reading can arise due to a general reduction of visual speed and span, and explain why this has a disproportionate impact on word reading while recognition of other visual stimuli are less obviously affected
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From word superiority to word inferiority: Visual processing of letters and words in Pure Alexia
Cognitive Neuropsychology, 2014Co-Authors: Thomas Habekost, Marlene Behrmann, Anders Petersen, Randi StarrfeltAbstract:Visual processing and naming of individual letters and short words were investigated in four patients with Pure Alexia. To test processing at different levels, the same stimuli were studied across a naming task and a visual perception task. The normal word superiority effect was eliminated in both tasks for all patients, and this pattern was more pronounced in the more severely affected patients. The relationship between performance with single letters and words was, however, not straightforward: One patient performed within the normal range on the letter perception task, while being severely impaired in letter naming and word processing, and performance with letters and words was dissociated in all four patients, with word reading being more severely impaired than letter recognition. This suggests that the word reading deficit in Pure Alexia may not be reduced to an impairment in single letter perception.
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How low can you go: spatial frequency sensitivity in a patient with Pure Alexia.
Brain and Language, 2013Co-Authors: Randi Starrfelt, Thomas Habekost, Simon D. Nielsen, Tobias S. AndersenAbstract:Abstract Pure Alexia is a selective deficit in reading, following lesions to the posterior left hemisphere. Writing and other language functions remain intact in these patients. Whether Pure Alexia is caused by a primary problem in visual perception is highly debated. A recent hypothesis suggests that a low level deficit – reduced sensitivity to particular spatial frequencies – is the underlying cause. We tested this hypothesis in a Pure alexic patient (LK), using a sensitive psychophysical paradigm to examine her performance with simple patterns of different spatial frequency. We find that both in a detection and a classification task, LK’s contrast sensitivity is comparable to normal controls for all spatial frequencies. Thus, reduced spatial frequency sensitivity does not constitute a general explanation for Pure Alexia, suggesting that the core deficit in this disorder is at a higher level in the visual processing stream.
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Word-superiority in Pure Alexia
Behavioural Neurology, 2013Co-Authors: Randi Starrfelt, Christian Gerlach, Thomas Habekost, Alexander P. LeffAbstract:Pure Alexia is an acquired reading disorder where patients lose the ability to read fast and fluently, but are commonly able to identify words letter-by-letter. This is evidenced by a pronounced word-length effect in reading, where reaction times (RTs) increase linearly with word length. The severity of the reading deficit in Pure Alexia has been reported to be systematically related to performanceon lexical and semantic decision tasks [1] and to visuoperceptual deficits [2]. Lesions to the suggested ‘visual word form area’ (VWFA) located in the left mid-fusiform gyrus seem to be of particular importance in causing Pure Alexia [3,4]. In the current study, we examine the word superiority effect (WSE) in four Pure alexic patients. The WSE refers to the phenomenon that normal readers are better at identifying letters embedded in words than in letter strings [5]. The effect is typically found in experiments where stimuli are presented briefly and then masked, followed by either a forced choice or free report task. There are a few case studies of the word-superiority effect in Pure Alexia (e.g. [6]) but findings so far have been contradictory. There have been no systematic attempts at linking performance in WSE experiments to visuoperceptual abilities or severity in Pure Alexia.
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Visual processing in Pure Alexia: a case study.
Cortex, 2009Co-Authors: Randi Starrfelt, Thomas Habekost, Christian GerlachAbstract:Whether Pure Alexia is a selective disorder that affects reading only, or if it reflects a more general visual disturbance, is highly debated. We have investigated the selectivity of visual deficits in a Pure alexic patient (NN) using a combination of psychophysical measures, mathematical modelling and more standard experimental paradigms. NN's naming and categorization of line drawings were normal with regards to both errors and reaction times (RTs). Psychophysical experiments revealed that NN's recognition of single letters at fixation was clearly impaired, and recognition of single digits was also affected. His visual apprehension span was markedly reduced for letters and digits. His reduced visual processing capacity was also evident when reporting letters from words. In an object decision task with fragmented pictures, NN's performance was abnormal. Thus, even in a Pure alexic patient with intact recognition of line drawings, we find evidence of a general visual deficit not selective to letters or words. This finding is important because it raises the possibility that other Pure alexics might have similar non-selective impairments when tested thoroughly. We argue that the general visual deficit in NN can be accounted for in terms of inefficient build-up of sensory representations, and that this low level deficit can explain the pattern of spared and impaired abilities in this patient.
