1,721,004 research outputs found
Disturbi dell'attenzione selettiva nella dislessia evolutiva: evidenze comportamentali, correlati neurobiologici, neurofisiologici e genetici
No full textReading acquisition requires not only adequate auditory-phonological skills, but also appropriate visuo-perceptual abilities. Some studies have shown that selective attention (SA) specifically affects these abilities. Although children and adults with developmental dyslexia (DD, neurodevelopmental reading deficit) show a phonological deficit, there are a number of theories supporting a non-linguistic sensory mechanisms (Dorsal-Magnocellular pathway, D-M). The non-linguistic deficit might in principal affect a general efficient processing of perceptual stimuli when spatial and temporal signal interference are induced by near noise. Some studies have shown that in individuals with DD, the deficit in reading is significantly affected by a sub-lexical damage. It is widely assumed that the sub-lexical route requires a primary graphemic parsing process (GP; i.e., the visual segmentation of a grapheme string into its constituent graphemes) provided by SA, in addition to phonological processing, memory and grapheme-phoneme correspondences.
Our studies attempted to investigate whether SA deficit, probably arised from a D-M dysfunction, could certainly have important consequences for normal reading developmental. SA deficit could selectively affect the rapid GP process necessary for an efficient phonological decoding. Precisely, a selective GP deficit might be due to a sluggish shifting of spatial (i.e., orienting and focusing processes) and temporal (i.e., engagement and disengagement processes) selective visual attention, which is a critical cognitive mechanism to support the perceptual signal processing and the noise exclusion induced by near letters.
The aim of this study is to investigate the potential neurobiologcal (i.e., D-M pathway), neurophysiological (i.e., early sensory modulation from posterior parietal cortex to occipital area) and molecular (i.e., cholinergic-nicotinic receptors) basis of the SA deficit in children with DD.
Our psychophysical and behavioral results coherently show that a specific spatial and temporal SA deficit, preventing an efficient GP (lead to all subsequent spelling-to-sound conversion processes), is specifically linked to a selective sub-lexical route damage (Experiments 1-6b). In dyslexics impaired in nonword reading (sub-lexical damage) the SA deficit might be linked to a neurodevelopmental deficit at D-M pathway (i.e., lower contrast sensitivity at frequency doubling illusion; Experiment 7a). In addition, an AS deficit seems to affect the signal discrimination ability and the perceptual lateral noise exclusion (Experiment 7b). Importantly, the study of lateral masking and text reading abilities confirms the potential predictive relation between spatial SA and the GP deficit in DD (Experiment 7c). Moreover, the results of visual event-related potential (ERP) study (Experiment 8) show a neurophysiological evidence of a sluggish shifting of visuo-spatial SA in dyslexics with a sub-lexical damage. Precisely, the facilitatory effect of visuo-spatial attention induced by a peripheral cue on the P1 (a early ERP of visual processing) is not present in dyslexics with a sub-lexical damage. Finally, the genetic study (Experiment 9) show that cholinergic-nicotinic receptors (i.e., polymorphism rs3827020 T/C, gene CHRNA4), affecting the intra-parietal lobe activity, might be linked to the visuo-spatial AS deficit and the specific reading deficit in DD.
In sum, our results provide psychophysics and behavioral evidences of spatial and temporal SA deficit in children with DD who are impaired in nonword reading. This deficit could be the result of a neurodevelopmental dysfunction of D-M pathway. Moreover, results from the lateral masking study suggest the possible causal relation between the spatial SA deficit and the specific phonological decoding damage, potentially affected by the GP process, which is requisite for the grapheme-phoneme mapping. Finally, we provide neurophysiological (P1 component) and molecular (cholinergic-nicotinic receptors) evidences that the sluggish of visuo-spatial SA might affect the efficiency of sub-lexical route, necessary to learn to read
Developmental dyslexia: Perceptual noise exclusion deficit or spatial attention dysfunction?
No full textDevelopmental dyslexia (DD) is characterized by a multi-sensory perceptual noise exclusion deficit. Indeed, dyslexics typically show a specific deficit in the ability to detect relevant stimuli (the signal) when spatiotemporal irrelevant stimuli (the noise) are closely presented. However, spatial attention seems to be the crucial process involved in perceptual noise exclusion and it has shown consistently impaired in dyslexics. The aim of the present study was to verify whether a defective automatic shifting of visual attention could explain the perceptual noise exclusion deficit in children with DD. Accuracy in identifying a target was measured in 31 dyslexics and 23 normally reading children by an experimental paradigm including two attentional (focused vs unfocused) and two noise conditions (signal vs signal plus lateral noise). Our results confirm, in children with DD, a specific target identification deficit when stimuli were displayed with lateral noise. More importantly, dyslexics were specifically impaired in the signal plus lateral noise only in focused attention, suggesting that the attentional shifting process could affect the general perceptual noise exclusion mechanism in DD
Visuospatial attention in pre-schoolers predicts reading acquisition
No full textDevelopmental dyslexia (DD) is a neurobiological disorder characterized by difficulty in reading acquisition despite adequate intelligence, conventional education and motivation. Impaired phonological processing is widely assumed to characterize dyslexic individuals. However, emerging evidence indicates that phonological problems and reading impairment both arise from poor visuo-orthographic coding. Reading acquisition, indeed, requires rapid selection of sublexical orthographic units through serial attentional orienting, and recent studies have shown that visuospatial attention is impaired not only in children with dyslexia but also in pre-readers at risk of dyslexia. The causal role of both phonological and visuospatial attention processing on reading acquisition was investigated in eighty-two pre-reader children. Here, we demonstrate for the first time that, although chronological age and nonverbal IQ as well as phonological processing were controlled for, pre-reading measures of visual parietal-attention functioning, as assessed by rapid peripheral object perception, spatial cueing facilitation and serial search skill, predict early literacy skills in Grade 1 and 2. Our findings provide evidence that—independently from the core phonological deficit—a visuo-attentional dysfunction may play a crucial role in reading failure, suggesting a new approach for a more efficient prevention of developmental dyslexia
Zoom-out attentional impairment in children with autism spectrum disorder
No full textAutism spectrum disorder (ASD) has long been associated with an inability to experience wholes without full attention to the constituent parts. A zoom-out attentional dysfunction might be partially responsible for this perceptual integration deficit in ASD. In the present study, the efficiency of attentional focusing mechanisms was investigated in children affected by ASD. We measured response latencies to a visual target onset displayed at three eccentricities from the fixation. Attentional resources were focused (zoom-in) or distributed (zoom-out) in the visual field presenting a small (containing only the nearest target eccentricity) or large (containing also the farthest target eccentricity) cue, 100 or 800 msec, before the target onset. Typically developing children, at the short cue-target interval, showed a gradient effect (i.e., latencies are slower at the farthest eccentricity) in the small focusing cue, but not in the large focusing cue condition. These results indicate an efficient zoom-in and zoom-out attentional mechanism. In contrast, children with ASD showed a gradient effect also in the large focusing cue condition, suggesting a specific zoom-out attentional impairment. In addition, the ASD group showed an atypical gradient effect at the long cue-target interval only in the small cue condition, suggesting a prolonged zoom-in and sluggish zoom-out attentional mechanism. This abnormal attentional focusing - probably linked to a dysfunctional top-down feedback from fronto-parietal network to the early visual areas - could contribute to the atypical visual perception associated to individuals with ASD which, in turn, could have consequences in their social-communicative development
Visual spatial attention and developmental reading disorder: A longitudinal study
No full textAlthough developmental dyslexia is often described as the result of a selective phonological deficit, visual magnocellular-dorsal (M-D) deficit hypothesis finds an increasing consent. Recent longitudinal studies pointed out that the M-D pathway plays a key role in the earliest and crucial reading acquisition phase. However, those studies do not address the exact neurocognitive mechanisms that lead from a low level impairment to a reading acquisition disorder. Grapheme–phoneme mapping requires, in addition to awareness of speech sounds, the attentional parsing of the letters strings into their graphemes. In particular, orienting of attention—mainly controlled by the M-D pathway—through letters strings, might represent the link between M-D pathway efficiency and reading acquisition outcome. To investigate this hypothesis, we measured in preschoolers the efficiency in orienting visual attention to a brief spatial exogenous cue. The prereaders were followed up and classified as poor or normal readers on the base of their reading abilities development during the first grade of primary school. Both linear and logistic regressions suggest that efficiency in orienting of visual attention is an effective predictor of reading acquisition outcome. These results support the hypothesis of a causal link between a spatial attention deficit and developmental dyslexia
Poor coherent motion discrimination is the consequence of magnocellular impairment in autism spectrum disorders?
No full textAutism spectrum disorder (ASD) has been associated to poor performance in a coherent dots motion detection task (CDM), a task that measures dorsal-stream sensitivity as well as fronto-parietal attentional processing. To clarify the role of spatial attention in the CDM task, we measured the perception of moving dots displayed in the central or in the peripheral visual field in ASD and typical development children. A dorsal-stream deficit in ASD children should predict generally worse performance in both conditions. However, we show that in ASD children the CDM perception was selectively impaired in the central condition. Moreover, in children with ASD, the central CDM efficiency was predicted by the ability to zoom out the attentional focus, measured combining an eccentricity effect with a cue-size paradigm. These findings suggest that a pure dorsal impairment could not completely explain poor CDM perception in ASD, but that the role of visual spatial attention in integrating the spatiotemporal information should also be taken into account
Sluggish engagement and disengagement of non-spatial attention in dyslexic children
No full textAlthough the dominant view posits that developmental dyslexia arises from a deficit in phonological
processing andmemory, efficient phonological decoding requires precise visual selection
of graphemes. Therefore, visual engagement and disengagement of non-spatial
attention were studied in 13 dyslexic children and 13 chronological age and intelligence quotient
(IQ) matched normally reading children by measuring ‘‘attentional masking’’ (AM) and
‘‘attentional blink’’ (AB) effects.AMrefers to an impaired identification of the first (T1) of two
rapidly sequential targets (i.e., attentional engagement). In contrast, AB refers to an impaired
identification of the second target in the sequence (T2; i.e., attentional disengagement). The
results revealed a specific temporal deficit ofAMas well as of AB in dyslexic children. Our results
showed that the abnormality in AM and AB is rather widespread, since 77% and 54% of
dyslexic children deviated at least 1 standard deviation (SD) from the mean of the controls,
respectively, for the two deficits. We further showed that individual differences in non-spatial
attention were specifically related to nonword reading ability. These results suggest that
non-spatial attention deficits (possibly related to a parietal cortex dysfunction) may selectively
impair the reading development via sub-lexical mechanisms
On the relationship between spatial and non-spatial attention
No full textSpatial attention orienting is known to enhance the signal in attended location as well as to exclude flanked noise. Moreover, spatial attention orienting is able to modulate the temporal processing, as suggested by the line motion illusion. Non-spatial attention is defined as the processing resources engagement onto the currently relevant object (measured by attentional masking) and processing resources disengagement from the previously relevant object (measured by attentional blink). In the present study we investigated the modulation of the spatial attention orienting on attentional masking. Spatial attention was manipulated by an exogenous (i.e., peripheral and non-informative) cue, while attentional masking was measured as the impaired identification of the first of two rapidly sequential objects. Results showed that, in the attended location, the non-spatial attention engagement on an object seems to occur faster (i.e., reduced attentional masking) than in the unattended location. We suggest that the spatial attention orienting is able to enhance the ability to rapidly engage non-spatial attention over time
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