What bilateral damage of the superior parietal lobes tells us about visual attention disorders in developmental dyslexia.

Neuroimaging studies have identified the superior parietal lobules bilaterally as the neural substrates of reduced visual attention (VA) span in developmental dyslexia. It remains however unclear whether the VA span deficit and the deficits in temporal and spatial attention shifting also reported in dyslexic children reflect a unitary spatio-temporal deficit of attention - probably linked to general posterior parietal dysfunction- or the dysfunction of distinct attentional systems that relate to different neural substrates. We explored this issue by testing an adult patient, IG, with a specific damage of the bilateral superior parietal lobules after stroke, on tasks assessing the VA span as well as temporal and spatial attention shifting. IG demonstrated a very severe VA span deficit, but preserved temporal attention shifting. Exogenous spatial orientation shifting was spared but her performance was impaired in endogenous attention. The overall findings show that distinct sub-systems of visual attention can be dissociated within the parietal lobe, suggesting that different attentional systems associated with specific neural networks can be selectively impaired in developmental dyslexia.

Enhancing reading performance through action video games: the role of visual attention span.

Recent studies reported that Action Video Game-AVG training improves not only certain attentional components, but also reading fluency in children with dyslexia. We aimed to investigate the shared attentional components of AVG playing and reading, by studying whether the Visual Attention (VA) span, a component of visual attention that has previously been linked to both reading development and dyslexia, is improved in frequent players of AVGs. Thirty-six French fluent adult readers, matched on chronological age and text reading proficiency, composed two groups: frequent AVG players and non-players. Participants performed behavioural tasks measuring the VA span, and a challenging reading task (reading of briefly presented pseudo-words). AVG players performed better on both tasks and performance on these tasks was correlated. These results further support the transfer of the attentional benefits of playing AVGs to reading, and indicate that the VA span could be a core component mediating this transfer. The correlation between VA span and pseudo-word reading also supports the involvement of VA span even in adult reading. Future studies could combine VA span training with defining features of AVGs, in order to build a new generation of remediation software.

Neural dissociation of phonological and visual attention span disorders in developmental dyslexia: FMRI evidence from two case reports.

A dissociation between phonological and visual attention (VA) span disorders has been reported in dyslexic children. This study investigates whether this cognitively-based dissociation has a neurobiological counterpart through the investigation of two cases of developmental dyslexia. LL showed a phonological disorder but preserved VA span whereas FG exhibited the reverse pattern. During a phonological rhyme judgement task, LL showed decreased activation of the left inferior frontal gyrus whereas this region was activated at the level of the controls in FG. Conversely, during a visual categorization task, FG demonstrated decreased activation of the parietal lobules whereas these regions were activated in LL as in the controls. These contrasted patterns of brain activation thus mirror the cognitive disorders' dissociation. These findings provide the first evidence for an association between distinct brain mechanisms and distinct cognitive deficits in developmental dyslexia, emphasizing the importance of taking into account the heterogeneity of the reading disorder.

Superior parietal lobule dysfunction in a homogeneous group of dyslexic children with a visual attention span disorder.

A visual attention (VA) span disorder has been reported in dyslexic children as potentially responsible for their poor reading outcome. The purpose of the current paper was to identify the cerebral correlates of this VA span disorder. For this purpose, 12 French dyslexic children with severe reading and VA span disorders and 12 age-matched control children were engaged in a categorisation task under fMRI. Two flanked and isolated conditions were designed which both involved multiple-element simultaneous visual processing but taxed visual attention differently. For skilled readers, flanked stimuli processing activated a large bilateral cortical network comprising the superior and inferior parietal cortex, the inferior temporal cortex, the striate and extrastriate visual cortex, the middle frontal cortex and the anterior cingulate cortex while the less attention-demanding task of isolated stimuli only activated the inferior occipito-temporal cortex bilaterally. With respect to controls, the dyslexic children showed significantly reduced activation within bilateral parietal and temporal areas during flanked processing, but no difference during the isolated condition. The neural correlates of the processes involved in attention-demanding multi-element processing tasks were more specifically addressed by contrasting the flanked and the isolated conditions. This contrast elicited activation of the left precuneus/superior parietal lobule in the controls, but not in the dyslexic children. These findings provide new insights on the role of parietal regions, in particular the left superior parietal lobule, in the visual attention span and in developmental dyslexia.

[The reader brain: natural and cultural story]. / Le cerveau lecteur : histoire naturelle et culturelle.

The report of cases of pure alexia suggests that some regions of the neural system are dedicated to reading-specific visual processing abilities. Pure alexia results from the disruption or the disconnection of the visual word form area, a region reproducibly located within the left occipito-temporal sulcus and encoding the abstract identity of strings of visual letters. The functional specialization of this area suggests that it is initially plastic and becomes attuned to the orthographic regularities that constrain letter combination during the acquisition of literacy. The visual word form area further belongs to the network of areas that are consistently implicated in studies of people with developmental dyslexia. Developmental dyslexia is typically interpreted as resulting from a core phonological disorder and most neuroimaging studies showed reduced activity in the left perisylvian regions which have a role in phonological processes. Although low level visual and/or visual attentional disorders have been consistently reported suggesting a visual basis of developmental dyslexia, these disorders typically co-occurred with phonological problems so that the phonological deficit was viewed as the most plausible cause of the poor reading outcome of dyslexic children. In the last years however, dissociations have been reported in developmental dyslexia between phonological processing deficits and a particular kind of visual disorder, a visual attention span deficit characterised by a reduction in the number of distinct orthographic units which can be processed simultaneously in a single fixation. Large sample studies revealed that a non trivial number of dyslexic children exhibit a visual attention span disorder and that this disorder typically dissociates from phonological impairments in the dyslexic population. Neuroimaging studies suggest involvement of the parietal lobes - in particular the superior parietal lobules - in visual attention span and these brain regions are less active in people with developmental dyslexia. A visual attention span disorder thus appears as a second core disorder related to a parietal dysfunction in developmental dyslexia. Further studies are required to determine whether the phonological disorder or the visual attention span disorder independently contribute to the development of the visual word form area during literacy acquisition. These neurobiological dysfunctions are further modulated by environmental factors such as language characteristics, remedial interventions or socio-economic status. Future studies would help better understanding the interactions between neurobiological and environmental factors and the potential influence of the later on the development of the visual word form area.

Lateral masking, levels of processing and stimulus category: a comparative study between normal and dyslexic readers.

The lateral masking effect results in lower performance on letter recognition when items are flanked by other stimuli. Using a new paradigm based on discrimination (feature analysis) and categorization (memory access) tasks, we investigated the influence of level of processing (as addressed, respectively, by these two tasks) and stimulus type (Latin letters, Korean letters and geometrical figures) on lateral masking. In addition, performance of dyslexic and non-dyslexic adult readers was compared. The non-dyslexic participants demonstrated a classical lateral masking effect with lower performance for flanked items than isolated ones. In addition, lateral masking was stronger in the categorization than in the discrimination task and was restricted to familiar items, i.e., Latin letters and geometrical figures. Dyslexic participants showed poorer performance than non-dyslexics on processing isolated items, and the pattern of decrease in performance for lateral masking was similar to non-dyslexics. However, they also showed a stronger decrease in performance in categorization and a stronger decrease related to the lateral masking for this categorization task. Our results in normal readers suggest that lateral masking relies on the interference between the target and the flankers during feature integration that may result in marked impairment of memory access (categorization task). Poorer performance in dyslexic readers may reflect impaired parafoveal/peripheral low-level processing during feature integration that may have worsened during the flanked condition due to a target selection/spatial-attentional disorder. Moreover, dyslexic subjects presented an additional categorization deficit that may relate to a specific left-hemispheric disorder.

Polysyllabic pseudo-word processing in reading and lexical decision: converging evidence from behavioral data, connectionist simulations and functional MRI.

The cognitive mechanisms involved in polysyllabic pseudo-word processing -- and their neurobiological correlates -- were studied through the analysis of length effects on French words and pseudo-words in reading and lexical decision. Connectionist simulations conducted on the ACV98 network paralleled the behavioral data in showing a strong length effect on naming latencies for pseudo-words only and the absence of length effect for both words and pseudo-words in lexical decision. Length effects in reading were characterized at the neurobiological level by a significant and specific activity increase for pseudo-words as compared to words in the right lingual gyrus (BA 19), the left superior parietal lobule and precuneus (BA7), the left middle temporal gyrus (BA21) and the left cerebellum. The behavioral results suggest that polysyllabic pseudo-word reading mainly relies on an analytic procedure. At the biological level, additional activations in visual and visual attentional brain areas during long pseudo-word reading emphasize the role of visual and visual attentional processes in pseudo-word reading. The present findings place important constraints on theories of reading in suggesting the involvement of a serial mechanism based on visual attentional processing in pseudo-word reading.

[Plurality of patterns of cognitive impairment in normal aging and in dementia]. / Pluralité des patrons d'atteinte cognitive accompagnant le vieillissement normal et la démence.

Normal aging, as well as most of the degenerative diseases of the central nervous system characterizing old age, have an impact on cognitive abilities which are obvious as well as increasingly understood. Cognitive changes in normal ageing realize a plurality of possible patterns of cognitive disabilities. Dementias are also well known to be characterized by a plurality of cognitive impairments patterns. The different cognitive patterns are likely to be due to distinct levels of impairments of different domains of cognition, or of different components within one given domain of cognition. These differences are such that in some cases they can even realize double dissociations. The plurality of cognitive impairments patterns in normal aging and in dementia will be discussed as well as the different factors that could contribute to such a plurality. Some of these factors relate to pre-morbid characteristics of the individuals known to influence the functional organization of the brain for cognition. Others--of major importance--are related to the nature and the distribution of the pathophysiological processes underlying normal ageing or a given degenerative disease. It is also reminded that some or many of these factors can interact with more general cognitive factors, such as speed of execution. It is however suggested that, despite of their presence, these general factors partly contribute to the cognitive impairments in neurodegenerative dementia. In this case, the impact of different disease-related factors over a general cognitive factor is probably much greater than in the case of normal aging.

A connectionist multiple-trace memory model for polysyllabic word reading.

A connectionist feedforward network implementing a mapping from orthography to phonology is described. The model develops a view of the reading system that accounts for both irregular word and pseudoword reading without relying on any system of explicit or implicit conversion rules. The model assumes, however, that reading is supported by 2 procedures that work successively: a global procedure using knowledge about entire words and an analytic procedure based on the activation of word syllabic segments. The model provides an account of the basic effects that characterize human skilled reading performance including a frequency by consistency interaction and a position-of-irregularity effect. Furthermore, early in training, the network shows a performance similar to that of less skilled readers. It also offers a plausible account of the patterns of acquired phonological and surface dyslexia when lesioned in different ways.

Heterogeneity in the cognitive profile of normal elderly.

An increasing number of studies point to the fact that distinct cognitive subgroups may be identified among subjects with dementia of the Alzheimer type (DAT). Although such heterogeneity could be the expression of neuropsychological, genetic, or epidemiological factors, the identification of neuropsychological subtypes in DAT could also reflect the existence of cognitive subgroups in a normal aged population. In the present study, the existence of neuropsychological subgroups was sought from among 81 volunteers aged between 55 and 84 years. Subjects were given a neuropsychological battery addressing various aspects of cognitive functioning. Results show that six subgroups could be identified among this population. Subgroups differ primarily in their overall degree of performance. Qualitative differences in cognitive performance are also present, mostly when subgroups which exhibit poor overall performance are considered. Consequently, the presence of such heterogeneity in normal elderly should be taken into account in any attempt to identify neuropsychologically based subgroups in early dementia of the Alzheimer type.