Temporal auditory processing at 17 months of age is associated with preliterate language comprehension and later word reading fluency: an ERP study.

Dyslexia is heritable and associated with auditory processing deficits. We investigate whether temporal auditory processing is compromised in young children at-risk for dyslexia and whether it is associated with later language and reading skills. We recorded EEG from 17 months-old children with or without familial risk for dyslexia to investigate whether their auditory system was able to detect a temporal change in a tone pattern. The children were followed longitudinally and performed an intelligence- and language development test at ages 4 and 4.5 years. Literacy related skills were measured at the beginning of second grade, and word- and pseudo-word reading fluency were measured at the end of second grade. The EEG responses showed that control children could detect the temporal change as indicated by a mismatch response (MMR). The MMR was not observed in at-risk children. Furthermore, the fronto-central MMR amplitude correlated with preliterate language comprehension and with later word reading fluency, but not with phonological awareness. We conclude that temporal auditory processing differentiates young children at risk for dyslexia from controls and is a precursor of preliterate language comprehension and reading fluency.

Information processing differences and similarities in adults with dyslexia and adults with Attention Deficit Hyperactivity Disorder during a Continuous Performance Test: a study of cortical potentials.

Twenty male adults with ADHD, 16 dyslexic adults, 15 comorbid adults, and 16 normal controls were compared on performance and underlying brain responses, during a cued Continuous Performance Test (O-X CPT), with the aim of discovering features of information processing differentiating between the groups. The study evaluated both cue- and target-related processes by analysing performance measures (errors, reaction time, and variability of reaction time), and event-related potentials (ERPs). Cue-related ERP components included the Cue-N2, Cue-P3, contingent negative variation (CNV) consisting of the CNV1, related to cue orienting, and the CNV2, related to response preparation. For targets, a distinction was made between response-related (Go), and inhibitory (Nogo) processing. Target-related components included the Go-P3, Nogo-N2, and Nogo-P3. Performance deficits were found only for the ADHD group, who demonstrated a faster decline in response speed with time-on-task and greater overall within-subject variability. No group differences were found for cue-related ERP components. Yet, controlling for group differences in internalising problems, inhibitory control was reduced in all clinical groups compared to controls, as demonstrated by an absence of frontal amplification of P3 in the Nogo condition, relative to the Go condition. For the ADHD group, in contrast to the comorbid and the dyslexic group, this effect remained after controlling for externalising symptoms, indicating that only for the ADHD group deficiencies in inhibitory control were not explained by externalising behaviour.

Reduced interhemispheric coherence in dyslexic adults.

INTRODUCTION: Developmental dyslexia has been associated with reduced interhemispheric neural connectivity in children. The present study investigated functional interhemispheric connectivity in male dyslexic adults. METHODS: A group of 19 dyslexic men were compared to a group of 15 controls on interhemispheric coherence of the dominant frequency in the power spectrum during a visuo-spatial attention task. The coherence between a left hemisphere central-parietal electrode and the respective right hemisphere electrode and surrounding sites was analysed. RESULTS: Compared to controls, the dyslexic group demonstrated reduced, and more diffuse, interhemispheric coherence of alpha activity in the central-parietal cortex. No group differences in interhemispheric coherence were found on frontal, temporal or central sites. CONCLUSIONS: The deviant pattern of functional connectivity in dyslexics is suggestive of an altered development of neural circuitry that may lead to deficits in magnocellular processing.

Distinct information processing characteristics in dyslexia and ADHD during a covert orienting task: an event-related potential study.

OBJECTIVE: A visuo-spatial orienting task was used to investigate the individual and joint contribution of the presence of dyslexia and attention-deficit hyperactivity disorder (ADHD) to information processing. METHODS: Sixteen control, 17 dyslexic, 16 ADHD, and 15 comorbid adults performed the task, comprising a valid, invalid, and no-cue condition. Performance measures were errors and reaction time (RT). A negative potential in response to cues and targets (N2), and a positive potential in response to targets (P3) were derived from the EEG. A 2x2 design was used with the factors dyslexic/non-dyslexic, and ADHD/non-ADHD. RESULTS: Dyslexic participants demonstrated a smaller cue-related N2, yet a greater target-related N2 in the valid condition. ADHD participants were discriminated by the P3 difference between the invalid and valid conditions. Comorbids differed from ADHD mainly in invalid-valid RT, and were similar to dyslexics in target N2 processing. CONCLUSIONS: Dyslexics were impaired in early information processing, and participants with ADHD differed for later processing stages. SIGNIFICANCE: This is the first ERP study of attentional processes in dyslexia to incorporate an ADHD and a comorbid group. Its results may contribute to differentiation of these clinical groups.

Differences in AERP responses and atypical hemispheric specialization in 17-month-old children at risk of dyslexia.

To determine the auditory event-related potential (AERP) correlates of phoneme perception in 17-month-old children at risk of dyslexia and controls, AERPs were elicited by standard (/bAk/) and deviant (/dAk/) word stimuli presented in an oddball paradigm. The at-risk children tended to show delayed P1 and P2 peaks for standard stimuli. Hemispheric group differences were observed for N2 amplitude and P1 latency, suggesting atypical processing of spoken words in at-risk children. Larger P2 and to a lesser extent P1 amplitudes following deviant words occurred in the control but not in the at-risk group, this may signal poorer phoneme discrimination in at-risk children. The present AERP results offer clues to where to look for a marker to identify children at high risk of reading and writing problems at an early age to facilitate early intervention.

Cortical categorization failure in 2-month-old infants at risk for dyslexia.

Cortical auditory categorization was assessed in 2-month-old infants at genetic risk for dyslexia and controls. Manipulated /bAk/ and /dAk/ speech stimuli were used as frequently presented standards. The neuroelectric brain responses of the control infants were highly sensitive to the phoneme boundary that separated these stimuli, but the infants at risk showed no signs of cortical categorical perception. Cortical sources of the responses were predominantly found in the left hemisphere for the control infants, but mainly in the right hemisphere for the infants at risk. The results demonstrate that impaired categorical perception in dyslexia is already present in infants at risk for the disorder.

Subject-verb agreement and phonological processing in developmental dyslexia and specific language impairment (SLI): a closer look.

BACKGROUND: Problems with subject-verb agreement and phonological (processing) skills have been reported to occur in children with specific language impairment (SLI) and in those with developmental dyslexia, but only a few studies have compared such problems in these two groups. Previous studies have claimed a causal relationship between phonological processing deficits and morphosyntactic problems. AIMS: The following questions were addressed in this study: (1) Are children with developmental dyslexia and SLI comparable in the level of sensitivity to subject-verb agreement, phonological awareness, and non-word repetition? (2) Are children with developmental dyslexia and SLI comparable in their performance profiles on tasks tapping subject-verb agreement, phonological awareness, and non-word repetition? (3) Are deficits in phonological processing skills related to morphosyntactic deficits? METHODS & PROCEDURES: Forty-five children (mean age = 8;6 years) with developmental dyslexia, SLI and typically developing children participated. The sensitivity to subject-verb agreement, phonological awareness, and non-word repetition was measured. OUTCOMES & RESULTS: Both the children with dyslexia and with SLI made more errors than the control children on the subject-verb agreement task, with the children with dyslexia scoring significantly better than the children with SLI. Similarly, the children with SLI and dyslexia both performed more poorly on the phoneme-deletion task than the control group. Both clinical groups performed more poorly on the non-word repetition task than the control children, with the children with dyslexia outperforming the children with SLI. In all three tasks differences in performance profiles were found between the children with developmental dyslexia and SLI. Across all three groups non-word repetition was correlated with morphosyntactic sensitivity. CONCLUSIONS: The results show similarities between the performances of children with SLI and dyslexia on tasks tapping subject-verb agreement, phonological awareness, and non-word repetition: they scored more poorly than typically developing children. Qualitative analyses revealed, however, differences in the error patterns on all three tasks. Associations between non-word repetition and sensitivity to subject-verb agreement were found, suggesting that problems with phonological processing impact on morphosyntactic skills.

Brain responses to subject-verb agreement violations in spoken language in developmental dyslexia: an ERP study.

This study investigates the presence and latency of the P600 component in response to subject-verb agreement violations in spoken language in people with and without developmental dyslexia. The two groups performed at-ceiling level on judging the sentences on their grammaticality, but the ERP data revealed subtle differences between them. The P600 tended to peak later in the left posterior region in the dyslexic group compared with the control group. In addition, the group of dyslexic subjects did not show a P600 in response to sentences with a plural NP subject. These results suggest that brain activation involved in syntactic repair is more affected by linguistic complexity in developmental dyslexia compared with non-dyslexic individuals.

Mismatch response is absent in 2-month-old infants at risk for dyslexia.

This study examined auditory processing in 2-month-old infants at genetic risk for dyslexia and in controls. Manipulated natural speech stimuli (/bAk/ and /dAk/), at either side of the phoneme boundary, were presented to these infants and their automatic cortical deviance responses were recorded. Control infants showed two distinct mismatch responses, thus extending similar findings reported with kindergartners in terms of topographical distribution and cortical sources. The absence of such mismatch responses in the infants at risk supports the hypothesis of basic auditory (temporal) processing impairments in the disorder. The results suggest that these early signs of deficient auditory processing may point to problematic categorical perception at a later age.

Differences at 17 months: productive language patterns in infants at familial risk for dyslexia and typically developing infants.

Productive vocabulary composition is investigated in 17-month-old children who are participating in an ongoing longitudinal dyslexia research project in the Netherlands. The project is searching for early precursors for dyslexia and follows a group of children who are genetically at risk for dyslexia and a control group during the first 10 years of their lives. Among other measures, the Dutch version of the MacArthur Communicative Development Inventory: Words and Sentences (N-CDI) is used to investigate early vocabulary development. In this article, the first N-CDI results from the 2 groups of 17-month-old children are compared with each other, with other cross-sectional, cross-linguistic studies, and with a similar Finnish longitudinal dyslexia project. The Dutch children show the same general acquisition pattern as documented for other languages, but there are significant differences between the two groups of 17-month-old children in total number of words produced and in the linguistic composition of their productive vocabulary.

Dyslexics show a deviant lateralization of attentional control: a brain potential study.

The present study compared performance and event-related brain potentials between dyslexic subjects and control subjects while they performed a spatial selective attention-shifting task. The subjects received a prestimulus cue on each trial, which indicated whether the subjects should attend to a position to the left of fixation or to the position at the opposite right of fixation. Thereafter a stimulus was presented either at the cued position or at the other position. In this paper we report on the brain activity in the cue-stimulus interval, which is supposed to reflect processes involved in controlling spatial attention shifting. The dyslexics performed much poorer on this task than the control subjects. The ERP-effects of cue direction closely resembled earlier reports, and consisted of an early (onset at about 200 ms) posterior contralateral negativity, a later (onset at about 350 ms) posterior contralateral positivity, and a later (onset at about 350 ms) frontal positivity. Dyslexics and controls differed with respect to the frontal attention effect. Whereas the controls showed this effect almost exclusively over the right hemisphere, the dyslexics showed both left and right hemispheric effects. We propose that this might support the idea that in dyslexia the development of interhemispheric asymmetry is disregulated.

Developmental dyslexia and discrimination in speech perception: a dynamic model study.

At the behavioral level one of the primary disturbances involved in congenital dyslexia concerns phonological processing. At the neuroarchitectural level autopsies have revealed ectopies, e.g., a reduced number of neurons in the upper layers of the cortex and an increased number in the lower ones. In dynamic models of interacting neuronal populations the behavioral level can be related to the neurophysiological level. In this study an attempt is made to do so at the cortical level. The first focus of this model study are the results of a Finnish experiment assessing geminate stop perception in quasi speech stimuli by 6 month old infants using a head turning paradigm and evoked potentials. The second focus of this study are the results of a Dutch experiment assessing discrimination of transients in speech stimuli, by adult dyslexics and controls and 2 month old infants. There appears to be a difference in the phonemic perceptual boundaries of children at genetic risk for dyslexia and control children as revealed in the Finnish study. Assuming a lowered neuronal density in the 'dyslexic' model, reflecting ectopies, it may be postulated that less neuronal surface is available for synaptic connections resulting in a lowered synaptic density and thus a lowered amount of available neurotransmitter. A lowered synaptic density also implies a reduced amount of membrane surface available for neurotransmitter metabolism. By assuming both, a reduced upper bound of neurotransmitter and a reduced metabolic transmitter rate in the dynamic model, the Finnish experimental results can be approximated closely. This applies both to data from behavioral head turning and that of the evoked potential study. In the Dutch study adult dyslexics show poor performance in discriminating transients in the speech signal compared to the controls. The same stimuli were used in a a study comparing infants from dyslexic families and controls. Using the same transmitter parameters as in modeling the results of the Finnish study, also in this case the experimental results for adults and infants can be approximated closely. Simulation of behavioral and pharmaceutical interventions with the model provide predictions which can be put to the test in experiments.