P. Been

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.

The Linear Logistic Test Model and heterogeneity of cognitive strategies

Some properties of the Linear Logistic Test Model (LLTM) are discussed. Two prerequisites should be met in order to test a cognitive model by means of the LLTM. First, the items used in testing the cognitive model should make up a Rasch homogeneous scale. Second, the population under consideration should be homogeneous with regard to the cognitive strategy employed in solving items representing the task at hand. For a task consisting of solving balance problems it is demonstrated that the second prerequisite is not fulfilled As a consequence the LLTM does not fit for the whole population. By dividing the population into four strategy homogeneous subpopulations a fitting LLTM could be found within one of these subpopulations. Consequently, it is recommended that in using the LLTM for testing cognitive models the population under consideration should be investigated with respect to different cognitive strategies.

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.

Development and application of a /bAk/–/dAk/ continuum for testing auditory perception within the Dutch longitudinal dyslexia study ☆

A national longitudinal research program on developmental dyslexia was started in The Netherlands, including auditory perception and processing as an important research component. New test materials had to be developed, to be used for measuring the auditory sensitivity of the subjects to speech-like stimuli from birth until the age of 10 years. This paper describes the subsequent steps and experiments in developing the auditory test material. Several experiments showed that dyslexic adults, as compared to a control group, were less accurate and slower in discriminating phoneme contrasts with subtle acoustic differences. The continuum developed so far, was tested in an experiment using a mismatch negativity paradigm applied in an adult control group. Results of this ERP study indicated that reliable mismatch negativity could be obtained which warrants the application of the paradigm and the stimuli to be appropriate for the currently running Dutch longitudinal dyslexia study.

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.

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.

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.

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 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.

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.