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Peter W Halligan - One of the best experts on this subject based on the ideXlab platform.
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Prism adaptation first among equals in alleviating Left Neglect: a review.
Restorative neurology and neuroscience, 2006Co-Authors: J. Luaute, Peter W Halligan, G. Rode, S. Jacquin-courtois, D. BoissonAbstract:Purpose: The current paper was designed to provide a critical overview on the different methods proposed for the rehabilitation of Left spatial Neglect. Methods: On the basis of a previous systematic review of the literature, we analyzed all articles available aiming at reducing Left spatial Neglect which included a long term functional assessment. Results: The aim of most early rehabilitation approaches, such as visuo-scanning training, was to re-orient visual scanning toward the Neglected side. This review confirmed the utility of this method for rehabilitation purposes. More recent - theory driven - procedures, also based on a training approach, include limb activation, mental imagery training and video-feedback training. Although there is ground for optimism, the functional effectiveness of these methods still relies on few single-case studies. Newer methods have tried to stimulate automatic orientation of gaze or attention towards Neglected space in a bottom-up fashion. Sensory stimulations can remove most of the classical signs of Left Neglect but their effects are short-lived. Such stimulations are not functionally relevant for rehabilitation except for trunk rotation or repeated neck muscle vibrations if they are associated with an extensive training program. A more promising intervention is prism adaptation given the growing evidence of relatively long-term functional gains from comparatively short term usage. Conclusion: Overall, there is now evidence for several clinically relevant long-term benefits in the case of visual scanning training, mental imagery training, video feedback training, neck muscle vibration and trunk rotation if associated with visual scanning training and prism adaptation. However, the amount of evidence is still limited to a small number of relevant published articles and it is mandatory to continue the research in this field. In this review, the possible routes for new rehabilitation procedures are discussed on the basis of the actual knowledge regarding the neuro-cognitive mechanisms underlying the therapeutic effect of prism adaptation.
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Neglected attention in apparent spatial compression
Neuropsychologia, 2004Co-Authors: Paolo Bartolomeo, Sylvie Chokron, Eric Siéroff, Marika Urbanski, Hanna Chainay, Christine Moroni, Catherine Belin, Peter W HalliganAbstract:Halligan and Marshall [Cortex 27 (1991) 623] devised a new test to evaluate the hypothesis that in visual Neglect, Left space is systematically compressed rightwards. In the critical condition of the original study, rows of horizontally arranged numbers with a target arrow pointing to one of them from the opposite margin of the display were presented. When asked to verbally identify the number indicated by the arrow, a right brain-damaged patient with Left Neglect and hemianopia often indicated a number to the right of the target. The more the target was located on the Left, the greater the response shift rightward, as if rightward compression were linearly proportional to the co-ordinates of Euclidian space. However, a possible alternative account could be that the patient’s attention was attracted by the numbers located to the right of the target digit, thus biasing her responses toward numbers on the right. To explore this hypothesis, we asked normal participants and patients with right hemisphere lesions, with and without Neglect or hemianopia, to mark on the margin of a sheet the approximate location indicated by an arrow situated on the opposite margin. In three different conditions, the arrow indicated either one of several numbers or lines in a row, or a blank location on the sheet margin. Only patients with Left Neglect, and especially those with associated hemianopia, deviated rightward, and then crucially only on those conditions where visible targets were present, consistent with the attentional bias account.
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Visuospatial Neglect: The Ultimate Deconstruction?
Brain and cognition, 1998Co-Authors: Peter W Halligan, John C. MarshallAbstract:Unilateral visuospatial Neglect is now widely acknowledged to be a highly heterogeneous condition: The overt manifestations of visual Neglect can vary as a function of task, spatial domain, and mode of response (at least). Double dissociations (sometimes of the strong form) have already been reported between most of the components of what was originally thought to be a relatively stable construct within the visual modality. Nonetheless, throughout successive fractionations of Neglect, reported cases of bidirectional task-specific Neglect after unilateral brain damage are rare. We now report two such cases. After right hemisphere stroke, the first patient reliably showed severe Left Neglect on cancellation but right Neglect on line bisection. After Left hemisphere stroke, the second case showed right Neglect on cancellation but Left Neglect on line bisection. Extensive investigation of case 1 confirmed our previous conjecture that the crucial distinction between these tasks lies in the presence or the absence of an overt target. In contrast to cancellation, line bisection demands the internal computation of the location of the “target” (the midpoint), followed by executing a motor response toward the precise location of that “imaginary” midpoint. The relative attentional and premotor contributions of the intact and damaged hemispheres to these forms of bidirectional Neglect are also assessed.
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Neglect of Awareness
Consciousness and cognition, 1998Co-Authors: Peter W Halligan, John C. MarshallAbstract:We describe some of the signs and symptoms of Left visuo-spatial Neglect. This common, severe and often long-lasting impairment is the most striking consequence of right hemisphere brain damage. Patients seem to (over-)attend to the right with subsequent inability to respond to stimuli in contralesional space. We draw particular attention to how patients themselves experience Neglect. Furthermore, we show that the Neglect patient's loss of awareness of Left space is crucial to an understanding of the condition. Even after Left space has been brought into the patient's consciousness (either by local cueing on the Left or by an emphasis on global properties of the scene as a whole), this awareness of Left space rapidly declines. We suggest that much of the symptomology of Left Neglect can be interpreted as a disconnection between brain mechanisms that are relatively specialized for local (detail) visual processing and global (panoramic) processing. This failure of communication between functional (subpersonal) mechanisms then has consequences for how perceptual and representational content enters into awareness. Failure of the local contents of Left space to be consciously accessed is, in turn, an important aspect of why Left Neglect is so difficult to remediate. Patients can “know” that they have Neglect but are cut off from the perceptual awareness that would enable them to overcome their attentional bias to the right.
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Grounding figural attention in Left Neglect
Neurocase, 1995Co-Authors: Peter W Halligan, John C. MarshallAbstract:Abstract The magnitude of Left visuo-spatial Neglect is sensitive to figural shape. Thus patients who bisect horizontal lines with a substantial rightward error may be significantly more accurate when marking the centre of squares. We now report a patient with gross Left Neglect after multiple right-hemisphere strokes whose impairment is quantitatively dependent upon the shape of the ground on which lines are presented for bisection. The modulatory effect obtained suggests that background ‘panoramic’ attention is still operative even in cases of very severe Neglect.
John C. Marshall - One of the best experts on this subject based on the ideXlab platform.
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Neglect of Awareness
Consciousness and cognition, 1998Co-Authors: Peter W Halligan, John C. MarshallAbstract:We describe some of the signs and symptoms of Left visuo-spatial Neglect. This common, severe and often long-lasting impairment is the most striking consequence of right hemisphere brain damage. Patients seem to (over-)attend to the right with subsequent inability to respond to stimuli in contralesional space. We draw particular attention to how patients themselves experience Neglect. Furthermore, we show that the Neglect patient's loss of awareness of Left space is crucial to an understanding of the condition. Even after Left space has been brought into the patient's consciousness (either by local cueing on the Left or by an emphasis on global properties of the scene as a whole), this awareness of Left space rapidly declines. We suggest that much of the symptomology of Left Neglect can be interpreted as a disconnection between brain mechanisms that are relatively specialized for local (detail) visual processing and global (panoramic) processing. This failure of communication between functional (subpersonal) mechanisms then has consequences for how perceptual and representational content enters into awareness. Failure of the local contents of Left space to be consciously accessed is, in turn, an important aspect of why Left Neglect is so difficult to remediate. Patients can “know” that they have Neglect but are cut off from the perceptual awareness that would enable them to overcome their attentional bias to the right.
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Visuospatial Neglect: The Ultimate Deconstruction?
Brain and cognition, 1998Co-Authors: Peter W Halligan, John C. MarshallAbstract:Unilateral visuospatial Neglect is now widely acknowledged to be a highly heterogeneous condition: The overt manifestations of visual Neglect can vary as a function of task, spatial domain, and mode of response (at least). Double dissociations (sometimes of the strong form) have already been reported between most of the components of what was originally thought to be a relatively stable construct within the visual modality. Nonetheless, throughout successive fractionations of Neglect, reported cases of bidirectional task-specific Neglect after unilateral brain damage are rare. We now report two such cases. After right hemisphere stroke, the first patient reliably showed severe Left Neglect on cancellation but right Neglect on line bisection. After Left hemisphere stroke, the second case showed right Neglect on cancellation but Left Neglect on line bisection. Extensive investigation of case 1 confirmed our previous conjecture that the crucial distinction between these tasks lies in the presence or the absence of an overt target. In contrast to cancellation, line bisection demands the internal computation of the location of the “target” (the midpoint), followed by executing a motor response toward the precise location of that “imaginary” midpoint. The relative attentional and premotor contributions of the intact and damaged hemispheres to these forms of bidirectional Neglect are also assessed.
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Grounding figural attention in Left Neglect
Neurocase, 1995Co-Authors: Peter W Halligan, John C. MarshallAbstract:Abstract The magnitude of Left visuo-spatial Neglect is sensitive to figural shape. Thus patients who bisect horizontal lines with a substantial rightward error may be significantly more accurate when marking the centre of squares. We now report a patient with gross Left Neglect after multiple right-hemisphere strokes whose impairment is quantitatively dependent upon the shape of the ground on which lines are presented for bisection. The modulatory effect obtained suggests that background ‘panoramic’ attention is still operative even in cases of very severe Neglect.
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Right-sided cueing can ameliorate Left Neglect
Neuropsychological Rehabilitation, 1994Co-Authors: Peter W Halligan, John C. MarshallAbstract:Abstract We report three cases of Left visuospatial Neglect after right hemisphere injury; the patients differ in severity and time post-insult. In the first experiment, all three patients showed a significant impairment on horizontal line bisection but were differentially sensitive to focal Left-sided cueing in this task. All three were considerably more accurate when requested to mark the centre of squares whose horizontal extent was identical to that of the previously employed lines. In the second experiment, two of the three patients also showed significant improvements on horizontal line bisection when a vertical line was positioned at the right end of the horizontal line; for one of these patients, no such improvement took place when an identical vertical line was placed at the Left end of the horizontal line. In the third experiment, we show that, for this latter patient, the extent of improvement is positively associated with the length of the vertical line in right space. The experiment also show...
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Toward a principled explanation of unilateral Neglect
Cognitive Neuropsychology, 1994Co-Authors: Peter W Halligan, John C. MarshallAbstract:Abstract In the unilateral Neglect syndrome, patients seem unable to detect or respond to stimuli in spatial locations contralateral to the damaged cerebral hemisphere. The condition has been reported in the visual, auditory, tactile, and olfactory modalities, although the most extensive investigations have concerned visuo-spatial Neglect. Left Neglect after right hemisphere lesion is more frequent, severe, and long-lasting than right Neglect after Left hemisphere lesion. Left Neglect is a major negative prognostic factor after brain damage and is reliably associated with poor performance on many functional recovery measures. Many current accounts stress that Neglect is an “attentional” disorder, although there are numerous (potentially competing) hypotheses that emphasise “perceptual,” “representational,” “intentional,” and “premotor” factors. In short, there is little theoretical consensus and it is possible that many distinct impairments have been conflated under the label of “unilateral Neglect.” The ...
Paolo Bartolomeo - One of the best experts on this subject based on the ideXlab platform.
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component deficits of visual Neglect magnetic attraction of attention vs impaired spatial working memory
Neuropsychologia, 2018Co-Authors: Monica N Toba, Christophe Duret, M Rabuffetti, Pascale Pradatdiehl, Guido Gainotti, Paolo BartolomeoAbstract:Visual Neglect is a disabling consequence of right hemisphere damage, whereby patients fail to detect Left-sided objects. Its precise mechanisms are debated, but there is some consensus that distinct component deficits may variously associate and interact in different patients. Here we used a touch-screen based procedure to study two putative component deficits of Neglect, rightward "magnetic" attraction of attention and impaired spatial working memory, in a group of 47 right brain-damaged patients, of whom 33 had signs of Left Neglect. Patients performed a visual search task on three distinct conditions, whereby touched targets could (1) be tagged, (2) disappear or (3) show no change. Magnetic attraction of attention was defined as more Left Neglect on the tag condition than on the disappear condition, where right-sided disappeared targets could not capture patients' attention. Impaired spatial working memory should instead produce more Neglect on the no change condition, where no external cue indicated that a target had already been explored, than on the tag condition. Using a specifically developed analysis algorithm, we identified significant differences of performance between the critical conditions. Neglect patients as a group performed better on the disappear condition than on the no change condition and also better in the tag condition comparing with the no change condition. No difference was found between the tag condition and the disappear condition. Some of our Neglect patients had dissociated patterns of performance, with predominant magnetic attraction or impaired spatial working memory. Anatomical results issued from both grey matter analysis and fiber tracking were consistent with the typical patterns of fronto-parietal and occipito-frontal disconnection in Neglect, but did not identify lesional patterns specifically associated with one or another deficit, thus suggesting the possible co-localization of attentional and working memory processes in fronto-parietal networks. These findings give support to the hypothesis of the co-occurrence of distinct cognitive deficits in visual Neglect and stress the necessity of multi-component models of visuospatial disorders.
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Effector-dependent Neglect and splenial disconnection: a spherical deconvolution tractography study
Experimental Brain Research, 2014Co-Authors: Marine Lunven, S. Jacquin-courtois, Paolo Bartolomeo, Michel Thiebaut Schotten, Bertrand Glize, Raffaella Migliaccio, François Cotton, G. RodeAbstract:We present the case of a patient with Left homonymous hemianopia and chronic Left Neglect consequent to a stroke in the occipito-temporal regions of the right hemisphere. When the patient performed cancellation tasks with her right (dominant) hand, she had severe and persistent Left Neglect at retest 7 and 8 years after onset. However, her performance on line bisection was invariably within normal limits. Strikingly, performance on cancellation tests reverted to normal when the patient used her Left hand. White matter tractography using spherical deconvolution demonstrated damage to the splenium of the corpus callosum, as well as a relative preservation of the right fronto-parietal network. Effector-dependent Neglect may occur because splenial disconnection deprives the right fronto-parietal network from visual information processed by the Left hemisphere. Consequently, spatial exploration reverts to normal when the patient uses her Left hand, thus involving more directly the fronto-parietal attentional networks in the right-hemisphere.
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Assessing the weights of visual Neglect: A new approach to dissociate defective symptoms from productive phenomena in length estimation
Neuropsychologia, 2010Co-Authors: Pom Charras, Juan Lupiáñez, Paolo BartolomeoAbstract:Right hemisphere damage often provokes signs of visual Neglect, characterized by a prominent Left-right imbalance in information processing. Neglect patients are biased towards right-sided objects and ignore Left-sided events. Left-right imbalance may not only result from Left Neglect but also from right attraction, which have been considered as, respectively, defective and productive phenomena in Neglect patients. However, the relative contributions of these two mechanisms to the final Left-right imbalance remain uncertain. Using a novel experimental paradigm, we were able to separately test the contribution of Left Neglect and right attraction to Neglect behavior. We used horizontal and vertical lines implemented in L shapes in a line extension task. The use of L shapes oriented either to the Left or to the right made it possible to measure the Left bias by comparing the length of a Left-sided horizontal line to that of a centered vertical line, and to measure the right bias by comparing a centered vertical to a rightwards horizontal line. Our results showed that, in this experimental set, the Left-right discrepancy is supported more by Left Neglect than by right attraction, with important implications about the role of Left-right competition on the deployment of Left Neglect and right attraction.
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Left visual Neglect: is the disengage deficit space- or object-based?
Experimental Brain Research, 2008Co-Authors: Federica Rastelli, Juan Lupiáñez, Maria-jesus Funes, Christophe Duret, Paolo BartolomeoAbstract:Attention can be directed to spatial locations or to objects in space. Patients with Left unilateral spatial Neglect are slow to respond to a Left-sided target when it is preceded by a right-sided “invalid” cue, particularly at short cue-target intervals, suggesting an impairment in disengaging attention from the right side in order to orient it Leftward. We wondered whether this deficit is purely spatial, or it is influenced by the presence of a right-sided visual object. To answer this question, we tested 10 right brain-damaged patients with chronic Left-Neglect and 41 control participants on a cued response time (RT) detection task in which targets could appear in either of two lateral boxes. In different conditions, non-informative peripheral cues either consisted in the brightening of the contour of one lateral box (onset cue condition), or in the complete disappearance of one lateral box (offset cue condition). The target followed the cue at different stimulus-onset asynchronies (SOAs). If the disengagement deficit (DD) is purely space-based, then it should not vary across the two cueing conditions. With onset cues, patients showed a typical DD at short SOAs. With offset cues, however, the DD disappeared. Thus, patients did not show any DD when there was no object from which attention must be disengaged. These findings indicate that the attentional bias in Left-Neglect does not concern spatial locations per se, but visual objects in space.
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Line bisection in Left Neglect: the importance of starting right.
Cortex; a journal devoted to the study of the nervous system and behavior, 2007Co-Authors: Marika Urbanski, Paolo BartolomeoAbstract:When marking the subjective midpoint of a horizontal line, patients with Left unilateral Neglect typically deviate rightward. Different accounts of this pattern of performance refer either to a biased competition between the two hemi-segments of the line, with the right part being subjectively perceived as longer than the Left part, or to a distortion of a cognitive representation of space, with spatial coordinates progressively relaxing from the right to the Left. These accounts make different predictions about the role of the right part of the line, which is crucial in the biased competition account, but less important in the distortion account. To test these predictions, we asked participants to set the endpoints and the centre of perceived and imaginary lines. Contrary to previous studies, we controlled for the direction of performance of the endpoint task, with Left-to-right trials and right-to-Left trials being performed in separate blocks. Five patients with right-hemisphere lesions and Left Neglect demonstrated the typical asymmetries when a right-sided stimulus (segment or endpoint) was present, but showed either normal performance or a reversed (Leftward) bias while setting the endpoints and the centre of an imaginary line starting from the Left side, when no right-sided visual stimulus was present until completion of each trial. We concluded that the right-sided portion of the line has a crucial importance in determining patients' rightward deviations in line bisection, consistent with the biased competition hypothesis and with neurocognitive models of attentional orienting.
Giuseppe Vallar - One of the best experts on this subject based on the ideXlab platform.
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Left Neglect dyslexia: Perseveration and reading error types.
Neuropsychologia, 2016Co-Authors: Roberta Ronchi, Lorella Algeri, Laura Chiapella, Marcello Gallucci, Maria Simonetta Spada, Giuseppe VallarAbstract:Right-brain-damaged patients may show a reading disorder termed Neglect dyslexia. Patients with Left Neglect dyslexia omit letters on the Left-hand-side (the beginning, when reading Left-to-right) part of the letter string, substitute them with other letters, and add letters to the Left of the string. The aim of this study was to investigate the pattern of association, if any, between error types in patients with Left Neglect dyslexia and recurrent perseveration (a productive visuo-motor deficit characterized by addition of marks) in target cancellation. Specifically, we aimed at assessing whether different productive symptoms (relative to the reading and the visuo-motor domains) could be associated in patients with Left spatial Neglect. Fifty-four right-brain-damaged patients took part in the study: 50 out of the 54 patients showed Left spatial Neglect, with 27 of them also exhibiting Left Neglect dyslexia. Neglect dyslexic patients who showed perseveration produced mainly substitution Neglect errors in reading. Conversely, omissions were the prevailing reading error pattern in Neglect dyslexic patients without perseveration. Addition reading errors were much infrequent. Different functional pathological mechanisms may underlie omission and substitution reading errors committed by right-brain-damaged patients with Left Neglect dyslexia. One such mechanism, involving the defective stopping of inappropriate responses, may contribute to both recurrent perseveration in target cancellation, and substitution errors in reading. Productive pathological phenomena, together with deficits of spatial attention to events taking place on the Left-hand-side of space, shape the manifestations of Neglect dyslexia, and, more generally, of spatial Neglect.
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Radial bisection of words and lines in right-brain-damaged patients with spatial Neglect.
Journal of neuropsychology, 2015Co-Authors: Laura Veronelli, Lisa S. Arduino, Luisa Girelli, Giuseppe VallarAbstract:The bisection of lines positioned radially (with the two ends of the line close and far, with respect to the participant's body) has been less investigated than that of lines placed horizontally (with their two ends Left and right, with respect to the body's midsagittal plane). In horizontal bisection, patients with Left Neglect typically show a rightward bias for both lines and words, greater with longer stimuli. As for radial bisection, available data indicate that neurologically unimpaired participants make a distal error, while results from right-brain-damaged patients with Left spatial Neglect are contradictory. We investigated the bisection of radially oriented words, with the prediction that, during bisection, linguistic material would be recoded to its canonical Left-to-right format in reading, with the performance of Neglect patients being similar to that for horizontal words. Thirteen right-brain-damaged patients (seven with Left spatial Neglect) and fourteen healthy controls were asked to manually bisect 40 radial and 40 horizontal words (5-10 letters), and 80 lines, 40 radial and 40 horizontal, of comparable length. Right-brain-damaged patients with spatial Neglect exhibited a proximal bias in the bisection of short radial words, with the proximal part corresponding to the final right part of horizontally oriented words. This proximal error was not found in patients without Neglect and healthy controls. For bisection, short radial words may be recoded to the canonical orthographic horizontal format, unveiling the impact of Left Neglect on radially oriented stimuli.
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Improving Left spatial Neglect through music scale playing
Journal of neuropsychology, 2015Co-Authors: Nicolò F. Bernardi, Roberta Ronchi, Maria Cristina Cioffi, Angelo Maravita, Emanuela Bricolo, Luca Zigiotto, Laura Perucca, Giuseppe VallarAbstract:The study assessed whether the auditory reference provided by a music scale could improve spatial exploration of a standard musical instrument keyboard in right-brain-damaged patients with Left spatial Neglect. As performing music scales involves the production of predictable successive pitches, the expectation of the subsequent note may facilitate patients to explore a larger extension of space in the Left affected side, during the production of music scales from right to Left. Eleven right-brain-damaged stroke patients with Left spatial Neglect, 12 patients without Neglect, and 12 age-matched healthy participants played descending scales on a music keyboard. In a counterbalanced design, the participants' exploratory performance was assessed while producing scales in three feedback conditions: With congruent sound, no-sound, or random sound feedback provided by the keyboard. The number of keys played and the timing of key press were recorded. Spatial exploration by patients with Left Neglect was superior with congruent sound feedback, compared to both Silence and Random sound conditions. Both the congruent and incongruent sound conditions were associated with a greater deceleration in all groups. The frame provided by the music scale improves exploration of the Left side of space, contralateral to the right hemisphere, damaged in patients with Left Neglect. Performing a scale with congruent sounds may trigger at some extent preserved auditory and spatial multisensory representations of successive sounds, thus influencing the time course of space scanning, and ultimately resulting in a more extensive spatial exploration. These findings offer new perspectives also for the rehabilitation of the disorder.
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Left Neglect dyslexia and the effect of stimulus duration
Neuropsychologia, 2005Co-Authors: Lisa S. Arduino, Giuseppe Vallar, Cristina BuraniAbstract:The present study investigated the effects of the duration of the stimulus on the reading performance of right-brain-damaged patients with Left Neglect dyslexia. Three Italian patients read aloud words and nonwords, under conditions of unlimited time of stimulus exposure and of timed presentation. In the untimed condition, the majority of the patients' errors involved the Left side of the letter string (i.e., Neglect dyslexia errors). Conversely, in the timed condition, although the overall level of performance decreased, errors were more evenly distributed across the whole letter string (i.e., visual - nonlateralized - errors). This reduction of Neglect errors with a reduced time of presentation of the stimulus may reflect the read out of elements of the letter string from a preserved visual storage component, such as iconic memory. Conversely, a time-unlimited presentation of the stimulus may bring about the rightward bias that characterizes the performance of Neglect patients, possibly by a capture of the patients' attention by the final (rightward) letters of the string.
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Reading aloud and lexical decision in Neglect dyslexia patients: a dissociation
Neuropsychologia, 2003Co-Authors: Lisa S. Arduino, Cristina Burani, Giuseppe VallarAbstract:Abstract This study investigated the dissociation between reading aloud and lexical decision in six Italian right-brain-damaged patients with Left Neglect dyslexia. Patients were requested to perform two tasks: (a) reading aloud and lexical decision on monomorphemic words of different frequencies and non-words with different degrees of similarity to real words (Experiment 1); (b) reading aloud and lexical decision on morphologically complex (suffixed) derived words and morphologically complex (suffixed) non-words (Experiment 2). The patients’ performance on lexical decision was compared to that of a group of matched control subjects. Patients showed Left Neglect dyslexia in the reading aloud task, but had a normal level of performance in the lexical decision task. Furthermore, patients were affected by the same morpho-lexical variables that influence lexical decision in normal subjects, suggesting a largely preserved morpho-lexical processing of written letter strings, as assessed by the task of lexical decision. The mechanisms underlying the preservation of lexical decision in patients with Left Neglect dyslexia are discussed in the light of dual route models of reading.
Sylvie Chokron - One of the best experts on this subject based on the ideXlab platform.
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ipsilesional deficit of selective attention in Left homonymous hemianopia and Left unilateral spatial Neglect
Neuropsychologia, 2019Co-Authors: Sylvie Chokron, Carole Peyrin, Celine PerezAbstract:Abstract Aims Patients with homonymous hemianopia may present a subtle ipsilesional deficit, recently referred to as ‘sightblindness’ in addition to the contralesional visual field defect. We recently demonstrated that this deficit could be worse in right brain-damaged patients with Left hemianopia than in Left brain-damaged patients with right hemianopia, confirming right hemisphere dominance for visuo-spatial and attentional capacities. In the present study we investigate whether this ipsilesional deficit could be attentional in nature and to what extent it is comparable in right brain-damaged (RBD) patients with Left hemianopia and in RBD patients with Left Neglect. The study was also conducted in RBD patients with neither Left hemianopia nor Left Neglect signs in order to test if a right hemisphere lesion per se could be responsible for subtle ipsilesional attentional deficit. To reach this aim, we tested selective attentional capacities in both visual fields of 10 right brain-damaged patients with Left Neglect (LN), 8 right brain-damaged patients with Left homonymous hemianopia (LHH), 8 right brain-damaged patients with no signs of Left Neglect or Left hemianopia (RBD controls), and 17 healthy age-matched participants (Normal controls). Method A lateralized letter-detection task was used to test if right-brain damaged patients with LN or LH may present a deficit of selective attention in their right, ipsilesional visual field, in comparison to Normal and RBD controls. Participants were asked to detect a target letter in either a single large stimulus (low attentional load) or a small stimulus surrounded by flankers (high attentional load). Stimuli were displayed either in the Left or in the right visual field. Accuracy and reaction times were recorded. Results Results on accuracy showed that both LN and LH patients exhibited lower correct responses than Normal controls in their ipsilesional right visual field, suggesting an attentional deficit in their ipsilesional, supposed healthy visual field. More specifically, LH patients exhibited a specific deficit for processing single large stimuli, but not for processing flanked stimuli, relative to normal controls. LN patients exhibited lower correct responses for processing all types of stimulus than normal controls, but also than right brain damaged controls, in both visual fields suggesting a non-lateralized deficit not only due to the right hemisphere lesion. Furthermore, this deficit is more pronounced for flanked small stimuli, requiring higher attentional load. Conclusions The present results bring further evidence that patients with Left homonymous hemianopia or Left unilateral Neglect both present a weaker but significant ipsilesional deficit in addition to their well-known massive contralesional deficit. The presence of a specific attentional deficit in the right ipsilesional visual field of Left hemianopic and Left Neglect patients is discussed regarding the hypothesis of hemispheric specialization for selective spatial attention and may have clinical implications for both conditions.
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Neglected attention in apparent spatial compression
Neuropsychologia, 2004Co-Authors: Paolo Bartolomeo, Sylvie Chokron, Eric Siéroff, Marika Urbanski, Hanna Chainay, Christine Moroni, Catherine Belin, Peter W HalliganAbstract:Halligan and Marshall [Cortex 27 (1991) 623] devised a new test to evaluate the hypothesis that in visual Neglect, Left space is systematically compressed rightwards. In the critical condition of the original study, rows of horizontally arranged numbers with a target arrow pointing to one of them from the opposite margin of the display were presented. When asked to verbally identify the number indicated by the arrow, a right brain-damaged patient with Left Neglect and hemianopia often indicated a number to the right of the target. The more the target was located on the Left, the greater the response shift rightward, as if rightward compression were linearly proportional to the co-ordinates of Euclidian space. However, a possible alternative account could be that the patient’s attention was attracted by the numbers located to the right of the target digit, thus biasing her responses toward numbers on the right. To explore this hypothesis, we asked normal participants and patients with right hemisphere lesions, with and without Neglect or hemianopia, to mark on the margin of a sheet the approximate location indicated by an arrow situated on the opposite margin. In three different conditions, the arrow indicated either one of several numbers or lines in a row, or a blank location on the sheet margin. Only patients with Left Neglect, and especially those with associated hemianopia, deviated rightward, and then crucially only on those conditions where visible targets were present, consistent with the attentional bias account.
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Visual, proprioceptive and tactile performance in Left Neglect patients.
Neuropsychologia, 2002Co-Authors: Sylvie Chokron, Pascale Colliot, Paolo Bartolomeo, François Rhein, Estelle Eusop, Philippe Vassel, Théophile OhlmannAbstract:Abstract Patients with unilateral spatial Neglect due to right-hemisphere lesions typically fail to attend to and explore Left-sided stimulus objects [32] . It has been postulated that in right-brain damaged (RBD) patients an ipsilesional displacement of the egocentric frame of reference (ER), whether visual or tactile, may be responsible for a contralesional supramodal spatial bias causing their Left Neglect behavior [39] . However, this hypothesis had been proposed without testing, in the same patients, the position of the ER or their performance in the visual and tactile modalities. Thus, the aim of the present study was to test the hypothesis that an ipsilateral shift of the ER is responsible for a supramodal spatial bias in Neglect. For this purpose, a within-subject design is required. Consequently, 12 Left Neglect patients and 12 control subjects were asked to perform a proprioceptive straight-ahead pointing task while blindfolded, as well as visual and tactile bisection tasks. In the Left Neglect patients, we found: (i) no systematic deviation of the ER on the ipsilesional right side; (ii) a significant rightward bias in visual bisection, and normal performance in tactile bisection; (iii) no correlation among the three tasks; (iv) that only visual bisection correlated with the severity of Neglect. These results are discussed with regard to the egocentric and attentional hypothesis of Neglect.
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Variability of response times as a marker of diverted attention.
Neuropsychologia, 2001Co-Authors: Paolo Bartolomeo, Sylvie Chokron, Eric Siéroff, Caroline DecaixAbstract:Abstract Anderson et al. (Variability not ability: another basis for performance decrements in Neglect. Neuropsychologia 2000;38:785–796) have recently reported that variability of response times (RTs) progressively increases from the right to the Left side in Left Neglect patients. Anderson et al. propose that this lack of consistency is an important determinant of patients’ behaviour, and may result from a deficit independent of other mechanisms causing Neglect. Here we suggest that an increase of variability, and not only of RTs, is to be expected when attention is exogenously biased away from the probed location. Consequently, space-based variability can be interpreted in the framework of existing models of unilateral Neglect. According to one such model, a basic impairment in Left Neglect is a bias toward rightward exogenous orienting of attention. As a result, Left targets often fail to rapidly capture patients’ attention, thus yielding slow RTs. However, since the probability for a Left target attracting attention is low but not null, relatively fast RTs can occur on those rare occasions in which a Left target does capture patients’ attention. The coexistence of these relatively fast with slow RTs could be at the basis of space-based variability in Neglect. Empirical support for our hypothesis comes from the results of a re-analysis for variability of cued RTs obtained in 18 normal individuals and six Left Neglect patients. Cues were peripheral and non-informative, thus eliciting an exogenous attentional shift. For normal individuals, invalid trials yielded less consistent response times than valid trials at short (150 ms) cue-target interval; for Neglect patients, a similar phenomenon occurred for Left invalidly-cued targets, thus paralleling the disproportionate cost in RTs typically evoked by this condition in unilateral Neglect. We conclude by discussing some possible determinants of gradient-shaped effects and by outlining the implications of space-based variability for current models of unilateral Neglect.
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Left unilateral Neglect or right hyperattention
Neurology, 1999Co-Authors: Paolo Bartolomeo, Sylvie ChokronAbstract:Background: Contradictory interpretations of Left unilateral Neglect suggest that it reflects either decreased attention toward the Left or increased attention toward the right. According to the right-hyperattention postulate, increasing severity of Neglect should result from an increasingly stronger bias toward the right. Thus, response times to right-sided targets should become progressively faster as Neglect increases in severity across patients. The Left-hypoattention postulate predicts that as Neglect increases, progressively less-attentional resources are deployed in both hemispaces. Thus, response times to right targets should progressively increase with increasing Neglect. Methods: We analyzed the distribution of manual response times to Left- and right-sided targets in 24 patients with right hemisphere lesions and varying degrees of Left Neglect. Results: Not only the responses to Left targets but also those to right targets became progressively slower as Neglect increased, consistent with the hypoattention account. However, the two regression lines were not parallel. With increasing Neglect, responses to Left targets increased more steeply than those to right targets did. Conclusions: A rightward attentional bias is present in patients with Left Neglect, together with Left hypoattention. However, this rightward bias is one of defective, and not enhanced, attention.