Impaired processing of rapid stimulus sequences in dyslexia

Evidence for impaired visuoperceptual organisation in developmental dyslexics and its relation to temporal processes

An analysis of normal and dyslexic readers' reaction-time (RT) performance in a standard visualdetection task (Experiment A) and in temporally primed visual detection (Experiment B) reveals a tendency for significantly longer search and detection RTs for dyslexic relative to the performance of normal readers. Consistent with previous studies, the RTs of normal readers and fast dyslexic responders exhibited target-specific priming effects. In contrast, in addition to increased but statistically insignificant target priming, a set of slower dyslexic responders showed strong negative priming on target-absent trials. In spite of the longer detection latencies produced by these dyslexic participants, no evidence was found to suggest that negative priming occurred as a general function of increasing difficulty in task performance (Experiment C). The enhanced positive and the negative priming effects are both interpreted in the context of the possible deployment of attentional mechanisms to the priming stimulus. The extent to which this strategy is characteristic of dyslexic performance as a whole may relate to the degree to which the dyslexic responder concerned experiences some general temporal processing impairment: Attentional deployment in this instance serving to compensate a lack of the requisite temporal resolution required for coding the spatiotemporal structure of the prime.

The neurophysiological basis of the integration of written and heard syllables in dyslexic adults

OBJECTIVE

Letter-speech sound integration in fluent readers takes place automatically and is dependent on temporal synchrony between letters and sounds. In developmental dyslexia, however, letter-speech sound associations are hard to learn, compromising accurate and fluent reading. We studied the effect of printed text on processing speech sounds in dyslexic and fluent adult readers.

METHODS

Visual stimuli were presented with sequences of spoken syllables including vowel or consonant changes, or changes in syllable intensity, frequency, or vowel duration. As visual material, written syllables or their scrambled images were used. The auditory stimuli were presented either synchronously with the visual stimuli or time delayed. The mismatch negativity (MMN), an index of automatic neural change detection, was recorded.

RESULTS

MMN amplitudes were larger to syllable changes in combination with written syllables than with scrambled images in fluent readers. However, dyslexic readers showed no difference between syllables vs. scrambled image condition. Furthermore, MMNs to consonant and frequency changes peaked later in dyslexic than fluent readers.

CONCLUSIONS

Our results suggest deficient and sluggish audiovisual integration in dyslexic individuals, which is not dependent on the phonological relevance of the deviant type.

SIGNIFICANCE

Unlike previous studies, our study included several different types of syllable changes presented with concurrent print, enabling us to determine in more detail the nature of the audiovisual deficit in dyslexia.

Grey matter alterations co-localize with functional abnormalities in developmental dyslexia: an ALE meta-analysis

The neural correlates of developmental dyslexia have been investigated intensively over the last two decades and reliable evidence for a dysfunction of left-hemispheric reading systems in dyslexic readers has been found in functional neuroimaging studies. In addition, structural imaging studies using voxel-based morphometry (VBM) demonstrated grey matter reductions in dyslexics in several brain regions. To objectively assess the consistency of these findings, we performed activation likelihood estimation (ALE) meta-analysis on nine published VBM studies reporting 62 foci of grey matter reduction in dyslexic readers. We found six significant clusters of convergence in bilateral temporo-parietal and left occipito-temporal cortical regions and in the cerebellum bilaterally. To identify possible overlaps between structural and functional deviations in dyslexic readers, we conducted additional ALE meta-analyses of imaging studies reporting functional underactivations (125 foci from 24 studies) or overactivations (95 foci from 11 studies ) in dyslexics. Subsequent conjunction analyses revealed overlaps between the results of the VBM meta-analysis and the meta-analysis of functional underactivations in the fusiform and supramarginal gyri of the left hemisphere. An overlap between VBM results and the meta-analysis of functional overactivations was found in the left cerebellum. The results of our study provide evidence for consistent grey matter variations bilaterally in the dyslexic brain and substantial overlap of these structural variations with functional abnormalities in left hemispheric regions.

Dysfunction of the auditory thalamus in developmental dyslexia

Developmental dyslexia, a severe and persistent reading and spelling impairment, is characterized by difficulties in processing speech sounds (i.e., phonemes). Here, we test the hypothesis that these phonological difficulties are associated with a dysfunction of the auditory sensory thalamus, the medial geniculate body (MGB). By using functional MRI, we found that, in dyslexic adults, the MGB responded abnormally when the task required attending to phonemes compared with other speech features. No other structure in the auditory pathway showed distinct functional neural patterns between the two tasks for dyslexic and control participants. Furthermore, MGB activity correlated with dyslexia diagnostic scores, indicating that the task modulation of the MGB is critical for performance in dyslexics. These results suggest that deficits in dyslexia are associated with a failure of the neural mechanism that dynamically tunes MGB according to predictions from cortical areas to optimize speech processing. This view on task-related MGB dysfunction in dyslexics has the potential to reconcile influential theories of dyslexia within a predictive coding framework of brain function.

Dissociation between the procedural learning of letter names and motor sequences in developmental dyslexia

Motor sequence learning has been studied extensively in Developmental dyslexia (DD). The purpose of the present research was to examine procedural learning of letter names and motor sequences in individuals with DD and control groups. Both groups completed the Serial Search Task which enabled the assessment of learning of letter names and motor sequences independently of each other. Control participants learned both the letter names as well as the motor sequence. In contrast, individuals with DD were impaired in learning of the letter names sequence and showed a reliable transfer of the motor sequence. Previous studies proved that motor sequence learning is impaired in DD. The present study demonstrated that this deficit is more pronounced when the task to be learned involves linguistic units. This result implies that the procedural learning system of language is more deficient than the motor procedural learning system in individuals with DD. The dissociation between motor and letter names sequence learning in those with DD also implies that the systems underlying these two tasks are separable.

Magno and parvo stimuli affect illusory directional hearing in normal and dyslexic readers

In an experimental paradigm adapted from Hari (1995), forty observers listened via headphones to 8 binaural clicks: 4 left-ear leading followed by 4 right-ear leading with either 38 or 140 ms interstimulus intervals (ISIs). Concurrently, they viewed either foveal or peripheral visual stimuli designed to activate either the parvocellular or magnocellular pathway. They then reported the perceived location of each click-pair. Our results replicated Hari's finding that observers mistake the perceived location of short ISI click-pairs more often than long. That is, when ISIs were short, the sounds seemed to play across the inside of the head in a phenomenon called illusory directional hearing. However, when click-pairs were accompanied by peripheral visual stimuli that activated the magnocellular pathway, observers were more accurate than when there were no visual stimuli. Conversely, parvocellular-activating foveal visual stimuli produced more illusory hearing than when there were no visual stimuli. These findings suggest that activating the slow sustained parvocellular system may result in a longer processing window. Thirty dyslexic observers who repeated the experimental paradigm had an even longer processing window than control observers indicating that dyslexics may have a magnocellular system deficit.

Impaired letter-string processing in developmental dyslexia: what visual-to-phonology code mapping disorder?

Poor parallel letter-string processing in developmental dyslexia was taken as evidence of poor visual attention (VA) span, that is, a limitation of visual attentional resources that affects multi-character processing. However, the use of letter stimuli in oral report tasks was challenged on its capacity to highlight a VA span disorder. In particular, report of poor letter/digit-string processing but preserved symbol-string processing was viewed as evidence of poor visual-to-phonology code mapping, in line with the phonological theory of developmental dyslexia. We assessed here the visual-to-phonological-code mapping disorder hypothesis. In Experiment 1, letter-string, digit-string and colour-string processing was assessed to disentangle a phonological versus visual familiarity account of the letter/digit versus symbol dissociation. Against a visual-to-phonological-code mapping disorder but in support of a familiarity account, results showed poor letter/digit-string processing but preserved colour-string processing in dyslexic children. In Experiment 2, two tasks of letter-string report were used, one of which was performed simultaneously to a high-taxing phonological task. Results show that dyslexic children are similarly impaired in letter-string report whether a concurrent phonological task is simultaneously performed or not. Taken together, these results provide strong evidence against a phonological account of poor letter-string processing in developmental dyslexia.

Are auditory and visual processing deficits related to developmental dyslexia?

The purpose of this study was to examine if children with dyslexia learning to read a consistent orthography (Greek) experience auditory and visual processing deficits and if these deficits are associated with phonological awareness, rapid naming speed and orthographic processing. We administered measures of general cognitive ability, phonological awareness, orthographic processing, short-term memory, rapid automatized naming, auditory and visual processing, and reading fluency to 21 Grade 6 children with dyslexia, 21 chronological age-matched controls and 20 Grade 3 reading age-matched controls. The results indicated that the children with dyslexia did not experience auditory processing deficits, but about half of them showed visual processing deficits. Both orthographic processing and rapid automatized naming deficits were associated with dyslexia in our sample, but it is less clear that they were associated with visual processing deficits.

The influence of contrast on coherent motion processing in dyslexia

The aim of the experiments was to investigate how manipulating the contrast of the signal and noise dots in a random dot kinematogram (RDK), influenced on motion coherence thresholds in adults with dyslexia. In the first of two experiments, coherent motion thresholds were measured when the contrasts of the signal and noise dots in an RDK were manipulated. A significantly greater processing benefit was found for the group with dyslexia than a control group when the signal dots were of higher contrast than the noise dots. However, a significant processing disadvantage was found for the group with dyslexia relative to the control group when the signal dots were of lower contrast than the noise dots. These findings were interpreted as supporting evidence for the noise exclusion hypothesis of dyslexia. In Experiment 2, the effect on coherent motion thresholds of presenting a cue that alerted observers to which stimuli, high or low contrast contained the signals dots was investigated. When the cue directed attention to low contrast signal dots presented in high contrast noise, coherent motion thresholds were only enhanced for the group with dyslexia. This manipulation produced equivalent coherent motion thresholds in the reader groups. In other conditions, the group with dyslexia had significantly higher coherent motion thresholds than the control group. It was concluded that adults with dyslexia who show evidence of a coherent motion deficit (37% of the dyslexia group in each experiment), have a specific difficulty in noise exclusion. This appears to occur as consequence of a sensory processing deficit in the magnocellular or dorsal stream.

How does information processing speed relate to the attentional blink?

Background

When observers are asked to identify two targets in rapid sequence, they often suffer profound performance deficits for the second target, even when the spatial location of the targets is known. This attentional blink (AB) is usually attributed to the time required to process a previous target, implying that a link should exist between individual differences in information processing speed and the AB.

Methodology/Principal Findings

The present work investigated this question by examining the relationship between a rapid automatized naming task typically used to assess information-processing speed and the magnitude of the AB. The results indicated that faster processing actually resulted in a greater AB, but only when targets were presented amongst high similarity distractors. When target-distractor similarity was minimal, processing speed was unrelated to the AB.

Conclusions/Significance

Our findings indicate that information-processing speed is unrelated to target processing efficiency per se, but rather to individual differences in observers' ability to suppress distractors. This is consistent with evidence that individuals who are able to avoid distraction are more efficient at deploying temporal attention, but argues against a direct link between general processing speed and efficient information selection.

Rhythmogram-based analysis for continuous electrographic data of the human brain

Ecologically relevant stimuli are rarely used in scientific studies because they are difficult to control. Instead, researchers employ simple stimuli with sharp boundaries (in space and time). Here, we explore how the rhythmogram can be used to provide much needed rigorous control of natural continuous stimuli like music and speech. The analysis correlates important features in the time course of stimuli with corresponding features in brain activations elicited by the same stimuli. Correlating the identified regularities of the stimulus time course with the features extracted from the activations of each voxel of a tomographic analysis of brain activity provides a powerful view of how different brain regions are influenced by the stimulus at different times and over different (user-selected) timescales. The application of the analysis to tomographic solutions extracted from magnetoencephalographic data recorded while subjects listen to music reveals a surprising and aesthetically pleasing aspect of brain function: an area believed to be specialized for visual processing is recruited to analyze the music after the acoustic signal is transformed to a feature map. The methodology is ideal for exploring processing of complex stimuli, e.g., linguistic structure and meaning and how it fails, for example, in developmental dyslexia.

The role of selective attention on academic foundations: a cognitive neuroscience perspective

To the extent that selective attention skills are relevant for academic foundations and amenable to training, they represent an important focus for the field of education. Here, drawing on research on the neurobiology of attention, we review hypothesized links between selective attention and processing across three domains important to early academic skills. First, we provide a brief review of the neural bases of selective attention, emphasizing the effects of selective attention on neural processing, as well as the neural systems important to deploying selective attention and managing response conflict. Second, we examine the developmental time course of selective attention. It is argued that developmental differences in selective attention are related to the neural systems important for deploying selective attention and managing response conflict. In contrast, once effectively deployed, selective attention acts through very similar neural mechanisms across ages. In the third section, we relate the processes of selective attention to three domains important to academic foundations: language, literacy, and mathematics. Fourth, drawing on recent literatures on the effects of video-game play and mind-brain training on selective attention, we discuss the possibility of training selective attention. The final section examines the application of these principles to educationally-focused attention-training programs for children.

A taxometric investigation of developmental dyslexia subtypes

Long-standing issues with the conceptualization, identification and subtyping of developmental dyslexia persist. This study takes an alternative approach to examine the heterogeneity of developmental dyslexia using taxometric classification techniques. These methods were used with a large sample of 671 children ages 6-8 who were diagnosed with severe reading disorders. Latent characteristics of the sample are assessed in regard to posited subtypes with phonological deficits and naming speed deficits, thus extending prior work by addressing whether these deficits embody separate classes of individuals. Findings support separate taxa of dyslexia with and without phonological deficits. Different latent structure for naming speed deficits was found depending on the definitional criterion used to define dyslexia. Non-phonologically based forms of dyslexia showed particular difficulty with naming speed and reading fluency.

Human ROBO1 regulates interaural interaction in auditory pathways

In rodents, the Robo1 gene regulates midline crossing of major nerve tracts, a fundamental property of the mammalian CNS. However, the neurodevelopmental function of the human ROBO1 gene remains unknown, apart from a suggested role in dyslexia. We therefore studied axonal crossing with a functional approach, based on magnetoencephalography, in 10 dyslexic individuals who all share the same rare, weakly expressing haplotype of the ROBO1 gene. Auditory-cortex responses were recorded separately to left- and right-ear sounds that were amplitude modulated at different frequencies. We found impaired interaural interaction that depended on the ROBO1 in a dose-dependent manner. Our results indicate that normal crossing of the auditory pathways requires an adequate ROBO1 expression level.

What are the causes of the attention deficits observed in children with dyslexia?

Dyslexic children often show attention problems at school, but it is not clear the nature of their impairments. The aim of this study was to analyze whether verbal processing artefacts could mediate attention deficits. Forty-seven children (22 dyslexics and 25 controls), aged between 7 to 12, were assessed through an ADHD rating scale and a battery of tasks tapping different attentional processes (selective, sustained, executive, and orienting). Phonological measures were used as covariates. Children with dyslexia showed attentional impairments (using both rating scales and neuropsychological tasks); however their performance was significantly affected by phonological performance. In conclusion, dyslexics may be inattentive at school because they are slow processors, in particular when they are presented with verbal stimuli.

Sound can improve visual search in developmental dyslexia

We examined whether developmental dyslexic adults suffer from sluggish attentional shifting (SAS; Hari and Renvall in Trends Cogn Sci 5:525-532, 2001) by measuring their shifting of attention in a visual search task with dynamic cluttered displays (Van der Burg et al. in J Exp Psychol Human 34:1053-1065, 2008). Dyslexics were generally slower than normal readers in searching a horizontal or vertical target among oblique distracters. However, the addition of a click sound presented in synchrony with a color change of the target drastically improved their performance up to the level of the normal readers. These results are in line with the idea that developmental dyslexics have specific problems in disengaging attention from the current fixation, and that the phasic alerting by a sound can compensate for this deficit.

Electrophysiological evidence for attenuated auditory recovery cycles in children with specific language impairment

Previous research indicates that at least some children with specific language impairment (SLI) show a reduced neural response when non-linguistic tones were presented at rapid rates. However, this past research has examined older children, and it is unclear whether such deficits emerge earlier in development. It is also unclear whether atypical refractory effects differ for linguistic versus non-linguistic stimuli or can be explained by deficits in selective auditory attention reported among children with SLI. In the present study, auditory refractory periods were compared in a group of 24 young children with SLI (age 3-8 years) and 24 matched control children. Event-related brain potentials (ERPs) were recorded and compared to 100 ms linguistic and non-linguistic probe stimuli presented at inter-stimulus intervals (ISIs) of 200, 500, or 1000 ms. These probes were superimposed on story narratives when attended and ignored, permitting an experimental manipulation of selective attention within the same paradigm. Across participants, clear refractory effects were observed with this paradigm, evidenced as a reduced amplitude response from 100 to 200 ms at shorter ISIs. Children with SLI showed reduced amplitude ERPs relative to the typically-developing group at only the shortest, 200 ms, ISI and this difference was over the left-hemisphere for linguistic probes and over the right-hemisphere for non-linguistic probes. None of these effects was influenced by the direction of selective attention. Taken together, these findings suggest that deficits in the neural representation of rapidly presented auditory stimuli may be one risk factor for atypical language development.

Sound can improve visual search in developmental dyslexia

We examined whether developmental dyslexic adults suffer from sluggish attentional shifting (SAS; Hari and Renvall in Trends Cogn Sci 5:525-532, 2001) by measuring their shifting of attention in a visual search task with dynamic cluttered displays (Van der Burg et al. in J Exp Psychol Human 34:1053-1065, 2008). Dyslexics were generally slower than normal readers in searching a horizontal or vertical target among oblique distracters. However, the addition of a click sound presented in synchrony with a color change of the target drastically improved their performance up to the level of the normal readers. These results are in line with the idea that developmental dyslexics have specific problems in disengaging attention from the current fixation, and that the phasic alerting by a sound can compensate for this deficit.

Attentional disengagement in adults with Williams syndrome

Williams syndrome (WS) is a neurodevelopmental disorder characterized by a distinctive behavioral and cognitive profile, including widespread problems with attention. However, the specific nature of their attentional difficulties, such as inappropriate attentional allocation and/or poor attentional disengagement abilities, has yet to be elucidated. Furthermore, it is unknown if there is an underlying difficulty with the temporal dynamics of attention in WS or if their attentional difficulties are task-dependent, because previous studies have examined attention in established areas of deficit and atypicality (specifically, visuospatial and face processing). In this study, we examined attentional processing in 14 adults with WS (20-59 years) and 17 typically developing controls (19-39 years) using an attentional blink (AB) paradigm. The AB is the decreased ability to detect a second target when it is presented in close proximity to an initial target. Overall, adults with WS had an AB that was prolonged in duration, but no different in magnitude, compared with typically developing control participants. AB performance was not explained by IQ, working memory, or processing speed in either group. Thus, results suggest that the attention problems in WS are primarily due to general attentional disengagement difficulties rather than inappropriate attentional allocation.

Mutation of the dyslexia-associated gene Dcdc2 impairs LTM and visuo-spatial performance in mice

Developmental reading disorder (RD) affects 5-10% of school aged children, with a heritability of approximately 60%. Genetic association studies have identified several candidate RD susceptibility genes, including DCDC2; however, a direct connection between the function of these genes and cognitive or learning impairments remains unclear. Variants in DCDC2, a member of the doublecortin family of genes, have been associated in humans with RD and ADHD and Dcdc2 may play a role in neuronal migration in rats. In this study, we examined the effect of Dcdc2 mutation on cognitive abilities in mice using a visual attention and visuo-spatial learning and memory task. We show that both heterozygous and homozygous mutations of Dcdc2 result in persistent visuo-spatial memory deficits, as well as visual discrimination and long-term memory deficits. These behavioral deficits occur in the absence of neuronal migration disruption in the mutant mice, and may be comorbid with an anxiety phenotype. These are the first results to suggest a direct relationship between induced mutation in Dcdc2 and changes in behavioral measures. Dcdc2 mutant mice should prove useful in future studies designed to further dissect the underlying neural mechanisms that are impaired following Dcdc2 mutation.

Do children with dyslexia and/or specific language impairment compensate for place assimilation? Insight into phonological grammar and representations

English speakers have to recognize, for example, that te[m] in te[m] pens is a form of ten, despite place assimilation of the nasal consonant. Children with dyslexia and specific language impairment (SLI) are commonly proposed to have a phonological deficit, and we investigate whether that deficit extends to place assimilation, as a way of probing phonological representations and phonological grammar. Children with SLI plus dyslexia, SLI only, and dyslexia only listened to sentences containing a target word in different assimilatory contexts-viable, unviable, and no change-and pressed a button to report hearing the target. The dyslexia-only group did not differ from age-matched controls, but the SLI groups showed more limited ability to accurately identify words within sentences. Once this factor was taken into account, the groups did not differ in their ability to compensate for assimilation. The results add to a growing body of evidence that phonological representations are not necessarily impaired in dyslexia. SLI children's results suggest that they too are sensitive to this aspect of phonological grammar, but are more liberal in their acceptance of alternative phonological forms of words. Furthermore, these children's ability to reject alternative phonological forms seems to be primarily limited by their vocabulary size and phonological awareness abilities.

Electrophysiological evidence for impaired attentional engagement with phonologically acceptable misspellings in developmental dyslexia

Event-related potential (ERP) studies of word recognition have provided fundamental insights into the time-course and stages of visual and auditory word form processing in reading. Here, we used ERPs to track the time-course of phonological processing in dyslexic adults and matched controls. Participants engaged in semantic judgments of visually presented high-cloze probability sentences ending either with (a) their best completion word, (b) a homophone of the best completion, (c) a pseudohomophone of the best completion, or (d) an unrelated word, to examine the interplay of phonological and orthographic processing in reading and the stage(s) of processing affected in developmental dyslexia. Early ERP peaks (N1, P2, N2) were modulated in amplitude similarly in the two groups of participants. However, dyslexic readers failed to show the P3a modulation seen in control participants for unexpected homophones and pseudohomophones (i.e., sentence completions that are acceptable phonologically but are misspelt). Furthermore, P3a amplitudes significantly correlated with reaction times in each experimental condition. Our results showed no sign of a deficit in accessing phonological representations during reading, since sentence primes yielded phonological priming effects that did not differ between participant groups in the early phases of processing. On the other hand, we report new evidence for a deficient attentional engagement with orthographically unexpected but phonologically expected words in dyslexia, irrespective of task focus on orthography or phonology. In our view, this result is consistent with deficiency in reading occurring from the point at which attention is oriented to phonological analysis, which may underlie broader difficulties in sublexical decoding.

Spatial layout of letters in nonwords affects visual short-term memory load: evidence from human electrophysiology

The sustained posterior contralateral negativity (SPCN) was used to investigate the effect of spatial layout on the maintenance of letters in VSTM. SPCN amplitude was measured for words, nonwords, and scrambled nonwords. We reexamined the effects of spatial layout of letters on SPCN amplitude in a design that equated the mean frequency of use of each position. Scrambled letters that did not form words elicited a larger SPCN than either words or nonwords, indicating lower VSTM load for nonwords presented in a typical horizontal array than the load observed for the same letters presented in spatially scrambled locations. In contrast, prior research has shown that the spatial extent of arrays of simple stimuli did not influence the amplitude of the SPCN. Thus, the present results indicate the existence of encoding and VSTM maintenance mechanisms specific to letter and word processing.

Dyslexic children show deficits in implicit sequence learning, but not in explicit sequence learning or contextual cueing

Dyslexia is a specific learning disability characterized by difficulties with accurate and/or fluent word recognition and by poor spelling abilities. The absence of other high level cognitive deficits in the dyslexic population has led some authors to propose that non-strategical processes like implicit learning could be impaired in this population. Most studies have addressed this issue by using sequence learning tasks, but so far the results have not been conclusive. We test this hypothesis by comparing the performance of dyslexic children and good readers in both implicit and explicit versions of the sequence learning task, as well as in another implicit learning task not involving sequential information. The results showed that dyslexic children failed to learn the sequence when they were not informed about its presence (implicit condition). In contrast, they learned without significant differences in relation to the good readers group when they were encouraged to discover the sequence and to use it in order to improve their performance (explicit condition). Moreover, we observed that this implicit learning deficit was not extended to other forms of non-sequential, implicit learning such as contextual cueing. In this case, both groups showed similar implicit learning about the information provided by the visual context. These results help to clarify previous contradictory data, and they are discussed in relation to how the implicit sequence learning deficit could contribute to the understanding of dyslexia.

Effects of sequential and discrete rapid naming on reading in Japanese children with reading difficulty

To clarify whether rapid naming ability itself is a main underpinning factor of rapid automatized naming tests (RAN) and how deep an influence the discrete decoding process has on reading, we performed discrete naming tasks and discrete hiragana reading tasks as well as sequential naming tasks and sequential hiragana reading tasks with 38 Japanese schoolchildren with reading difficulty. There were high correlations between both discrete and sequential hiragana reading and sentence reading, suggesting that some mechanism which automatizes hiragana reading makes sentence reading fluent. In object and color tasks, there were moderate correlations between sentence reading and sequential naming, and between sequential naming and discrete naming. But no correlation was found between reading tasks and discrete naming tasks. The influence of rapid naming ability of objects and colors upon reading seemed relatively small, and multi-item processing may work in relation to these. In contrast, in the digit naming task there was moderate correlation between sentence reading and discrete naming, while no correlation was seen between sequential naming and discrete naming. There was moderate correlation between reading tasks and sequential digit naming tasks. Digit rapid naming ability has more direct effect on reading while its effect on RAN is relatively limited. The ratio of how rapid naming ability influences RAN and reading seems to vary according to kind of the stimuli used. An assumption about components in RAN which influence reading is discussed in the context of both sequential processing and discrete naming speed.

Does a sensory processing deficit explain counting accuracy on rapid visual sequencing tasks in adults with and without dyslexia?

The experiments conducted aimed to investigate whether reduced accuracy when counting stimuli presented in rapid temporal sequence in adults with dyslexia could be explained by a sensory processing deficit, a general slowing in processing speed or difficulties shifting attention between stimuli. To achieve these aims, the influence of the inter-stimulus interval (ISI), stimulus duration, and sequence length were evaluated in two experiments. In the first that used skilled readers only, significantly more errors were found with presentation of long sequences when the ISI or stimulus durations were short. Experiment 2 used a wider range of ISIs and stimulus durations. Compared to skilled readers, a group with dyslexia had reduced accuracy on two-stimulus sequences when the ISI was short, but not when the ISI was long. Although reduced accuracy was found on all short and long sequences by the group with dyslexia, when performance on two-stimulus sequences was used as an index of sensory processing efficiency and controlled, group differences were found with presentation of stimuli of short duration only. We concluded that continuous, repetitive stimulation to the same visual area can produce a capacity limitation on rapid counting tasks in all readers when the ISIs or stimulus durations are short. While reduced accuracy on rapid sequential counting tasks can be explained by a sensory processing deficit when the stimulus duration is long, slower processing speed in the group with dyslexia explains the greater inaccuracy found as sequence length is increased when the stimulus duration is short.

Is developmental dyslexia modality specific? A visual-auditory comparison of Italian dyslexics

Although developmental dyslexia is often referred to as a cross-modal disturbance, tests of different modalities using the same stimuli are lacking. We compared the performance of 23 children with dyslexia and 42 chronologically matched control readers on reading versus repetition tasks and visual versus auditory lexical decision using the same stimuli. With respect to control readers, children with dyslexia were impaired only on stimuli in the visual modality; they had no deficit on the repetition and auditory lexical decision tasks. By applying the rate-amount model (Faust et al., 1999), we showed that performance of children with dyslexia on visual (but not auditory) tasks was associated with that of control readers by a linear relationship (with a 1.78 slope), suggesting that a global factor accounts for visual (but not auditory) task performance. We conclude that the processing of linguistic stimuli in the visual and auditory modalities is carried out by independent processes and that dyslexic children have a selective deficit in the visual modality.

Neuropsychological treatment of dyslexia: does type of treatment matter?

In this study, 123 children with a diagnosis of developmental dyslexia were assigned to different treatment groups, either variations of Bakker's intervention program based on the balance model or a control, a specific reading training group. Thorough cognitive and neuropsychological assessment allowed determination of the subtype of dyslexia according to the balance model and the neuropsychological profile with respect to reading and spelling abilities, verbal memory, and phonemic awareness. Characteristics of hemisphere-specific stimulation were systematically manipulated in an effort to shed light on the bases and mechanisms of reading improvement. It was shown that the effects of treatment vary according to type of dyslexia and that the different intervention programs have differential effects on reading-related neuropsychological functions. Since opposite effects can be produced by the same type of treatment in different dyslexia subtypes, the results of the study suggest that accurate classification of subtype on the base of reading and reading-related variables is advantageous for an optimal planning of the therapy.

Neurokognitive Korrelate der Dyslexie

Die Überblicksarbeit widmet sich kognitiven und neuronalen Grundlagen der Dyslexie. Ausgehend von einer Darstellung der wichtigsten kognitiven und neurobiologischen Theorien der Entstehung von Dyslexie werden Ergebnisse zu spezifischen Störungen des neuronalen Lesenetzwerks bei Menschen mit Dyslexie aus Postmortem-Untersuchungen und strukturellen sowie funktionellen Bildgebungsstudien berichtet. Die Befunde legen nahe, dass Dyslexie ein multidimensionales Problem darstellt, das mit verschiedenen kognitiven, sensorischen und motorischen Defiziten und spezifischen Störungen auf neuronaler Ebene einhergeht. Zukünftige Forschung sollte sich daher verstärkt individuellen Profilen der Störung auf kognitiver wie neuronaler Ebene widmen.

Binding of sights and sounds: age-related changes in multisensory temporal processing

We live in a multisensory world and one of the challenges the brain is faced with is deciding what information belongs together. Our ability to make assumptions about the relatedness of multisensory stimuli is partly based on their temporal and spatial relationships. Stimuli that are proximal in time and space are likely to be bound together by the brain and ascribed to a common external event. Using this framework we can describe multisensory processes in the context of spatial and temporal filters or windows that compute the probability of the relatedness of stimuli. Whereas numerous studies have examined the characteristics of these multisensory filters in adults and discrepancies in window size have been reported between infants and adults, virtually nothing is known about multisensory temporal processing in childhood. To examine this, we compared the ability of 10 and 11 year olds and adults to detect audiovisual temporal asynchrony. Findings revealed striking and asymmetric age-related differences. Whereas children were able to identify asynchrony as readily as adults when visual stimuli preceded auditory cues, significant group differences were identified at moderately long stimulus onset asynchronies (150-350 ms) where the auditory stimulus was first. Results suggest that changes in audiovisual temporal perception extend beyond the first decade of life. In addition to furthering our understanding of basic multisensory developmental processes, these findings have implications on disorders (e.g., autism, dyslexia) in which emerging evidence suggests alterations in multisensory temporal function.

Dyslexia in regular orthographies: manifestation and causation

This article summarizes our research on the manifestation of dyslexia in German and on cognitive deficits, which may account for the severe reading speed deficit and the poor orthographic spelling performance that characterize dyslexia in regular orthographies. An only limited causal role of phonological deficits (phonological awareness, phonological STM, and rapid naming) for the emergence of reading fluency and spelling deficits is inferred from two large longitudinal studies with assessments of phonology before learning to read. A review of our cross-sectional studies provides no support for several cognitive deficits (visual-attention deficit, magnocellular dysfunction, skill automatization deficit, and visual-sequential memory deficit), which were proposed as alternatives to the phonological deficit account. Finally, a revised version of the phonological deficit account in terms of a dysfunction in orthographic-phonological connectivity is proposed.

Coherence motion perception in developmental dyslexia: a meta-analysis of behavioral studies

The magnitude of the association between developmental dyslexia (DD) and motion sensitivity is evaluated in 35 studies, which investigated coherence motion perception in DD. A first analysis is conducted on the differences between DD groups and age-matched control (C) groups. In a second analysis, the relationship between motion coherence threshold and reading ability is considered. Globally, the mean effect size (ES) is moderate (d = 0.675, 2334 subjects) with a large value (d = 0.747) for the between-groups differences in motion perception and a smaller mean ES (d = 0.178) for the correlational studies. The influence on ES of the stimuli parameters and subjects age is analyzed. The number of dots, the age of the subjects, and the type of analysis (i.e. between-group or correlational) are significantly related to the ES. Looking at the ES values, a smaller number of dots constituting the stimuli are associated with larger ES and, interestingly, the children studies are associated with lower ES in comparison with the researches evaluating adults. The large ES value supports the importance of studying motion perception deficits in DD groups, consistently with the claim that dorsal impairment/noise-exclusion deficit could be one of the risk factor of reading difficulties.

Atypical EEG beta asymmetry in adults with ADHD

BACKGROUND

Abnormal brain laterality (ABL) is well established in ADHD. However, its clinical specificity and association to cognitive and clinical symptoms is not yet understood. Previous studies indicate increased right hemisphere (RH) contribution in both ADHD and reading impaired samples. The current study investigates whether this ABL characteristic occurs in adults with ADHD absent comorbid language impairment.

METHODS

EEG beta asymmetry was compared in 35 adult ADHD subjects and 104 controls during rest and active cognition. Group differences in beta asymmetry were then further evaluated for association to linguistic and attentional abilities, as well as association to beta asymmetry measures across different brain regions.

RESULTS

Adults with ADHD showed pronounced rightward beta asymmetry (p=.00001) in inferior parietal regions (P8-P7) during a continuous performance task (CPT) that could not be attributed to linguistic ability. Among ADHD subjects only, greater rightward beta asymmetry at this measure was correlated with better CPT performance. Furthermore, this measure showed a lack of normal association (i.e., observed in controls) to left-biased processing in temporal-parietal (TP8-TP7) brain regions important for higher order language functions.

CONCLUSION

Adult ADHD involves abnormally increased right-biased contribution to CPT processing that could not be attributed to poor language ability. This appears to also involve abnormal recruitment of LH linguistic processing regions and represents an alternative, albeit less effective, CPT processing strategy. These findings suggest different pathophysiologic mechanisms likely underlie RH biased processing in ADHD and reading impaired samples.

Interaction of phonological awareness and 'magnocellular' processing during normal and dyslexic reading: behavioural and fMRI investigations

We investigated whether phonological deficits are a consequence of magnocellular processing deficits in dyslexic and control children. In Experiment 1, children were tested for reading ability, phonological awareness, visuo-magnocellular motion perception, and attention shifting (sometimes considered as magnocellular function). A two-step cluster analysis of the behavioural scores revealed four clusters of children. Phonological awareness was correlated with attention (cluster musical sharp1) or motion detection (cluster musical sharp2), whereas attention and motion detection were correlated in cluster musical sharp3. In cluster musical sharp4, all variables were uncorrelated. In Experiment 2, the same variables plus auditory discrimination were tested with fMRI in a sub-sample of Experiment 1. Although dyslexics had reduced activation in visual or auditory cortex during motion detection or auditory discrimination, respectively, they had increased right frontal activation in areas 44 and 45 in all 'magnocellular' (including auditory) tasks. In contrasts, during phonological decisions, there was higher activation for good readers than dyslexics in left areas 44 and 45. Together, the two experiments give insight into the interplay of phonological and magnocellular processing during reading. Distinct left versus right frontal effects reveal partly different underlying neural mechanisms. These data contradict the view that phonological processing deficits in dyslexia necessarily result from impaired magnocellular functioning.

Visual spatial attention and speech segmentation are both impaired in preschoolers at familial risk for developmental dyslexia

Phonological skills are foundational of reading acquisition and impaired phonological processing is widely assumed to characterize dyslexic individuals. However, reading by phonological decoding also requires rapid selection of sublexical orthographic units through serial attentional orienting, and recent studies have shown that visual spatial attention is impaired in dyslexic children. Our study investigated these different neurocognitive dysfunctions, before reading acquisition, in a sample of preschoolers including children with (N=20) and without (N=67) familial risk for developmental dyslexia. Children were tested on phonological skills, rapid automatized naming, and visual spatial attention. At-risk children presented deficits in both visual spatial attention and syllabic segmentation at the group level. Moreover, the combination of visual spatial attention and syllabic segmentation scores was more reliable than either single measure for the identification of at-risk children. These findings suggest that both visuo-attentional and perisylvian-auditory dysfunctions might adversely affect reading acquisition, and may offer a new approach for early identification and remediation of developmental dyslexia.

Visual attentional blink in dyslexic children: Parameterizing the deficit

The parameters generated by a curve fitting method on the visual attentional blink (AB) of 14 dyslexic and 14 control children were compared. The two groups differed on AB minimum parameters, whereas both AB duration and AB amplitude parameters were the same. The results suggest that low AB minimum is associated with poor reading. Moreover, phonological awareness was found to correlate with visual AB parameters in the dyslexic group. Overall, the present study provides new methodological insights regarding the assessment of the AB and visual sequential processing in relation to reading disorders.