Global processing speed in children with low reading ability and in children and adults with typical reading ability: exploratory factor analytic models

Dyslexia, the Amsterdam Way

The current aim is to illustrate our research on dyslexia conducted at the Developmental Psychology section of the Department of Psychology, University of Amsterdam, in collaboration with the nationwide IWAL institute for learning disabilities (now RID). The collaborative efforts are institutionalized in the Rudolf Berlin Center. The first series of studies aimed at furthering the understanding of dyslexia using a gamified tool based on an artificial script. Behavioral measures were augmented with diffusion modeling in one study, and indices derived from the electroencephalogram were used in others. Next, we illustrated a series of studies aiming to assess individuals who struggle with reading and spelling using similar research strategies. In one study, we used methodology derived from the machine learning literature. The third series of studies involved intervention targeting the phonics of language. These studies included a network analysis that is now rapidly gaining prominence in the psychopathology literature. Collectively, the studies demonstrate the importance of letter-speech sound mapping and word decoding in the acquisition of reading. It was demonstrated that focusing on these abilities may inform the prediction, classification, and intervention of reading difficulties and their neural underpinnings. A final section examined dyslexia, conceived as a neurobiological disorder. This analysis converged on the conclusion that recent developments in the psychopathology literature inspired by the focus on research domain criteria and network analysis might further the field by staying away from longstanding debates in the dyslexia literature (single vs. a multiple deficit, category vs. dimension, disorder vs. lack of skill).

20 years on: Confirmation of P. Anderson's (2002) paediatric model of executive functioning in a healthy adult sample

Executive Functioning (EF) is a construct that encompasses multiple interrelated higher order skills, however, conceptualising this nebulous construct remains challenging. This study aimed to confirm the validity of Anderson's (2002) paediatric model of EF in a healthy adult sample using congeneric modelling. Measures of EF were selected based on utility with adult populations giving rise to minor methodological differences from the original paper. Separate congeneric models were constructed using each of Anderson's constructs in order to isolate the sub-skills represented by each (Attentional Control-AC, Cognitive Flexibility-CF, Information Processing-IP, Goal Setting-GS), with a minimum of three tests per subskill. One hundred and thirty-three adults (42 males and 91 females) aged between 18 and 50 (M = 29.68, SD = 7.46) completed a cognitive test battery comprising 20 EF tests. AC revealed a good fitting model χ²(2) = 1.61, p = .447, RMSEA = 0.000, CFI = 1.000, after removing the non-significant indicator Map Search (p = .349), and BS-Bk as BS-Bk was required to covary with both BS-Fwd (M.I = 7.160, Par Change = .706), and TMT-A (M.I = 5.759, Par Change = -2.417). CF revealed a good fitting model χ²(8) = 2.90, p = .940, RMSEA = 0.000, CFI = 1.000 after covarying TSC-E and Stroop (M.I = 9.696, Par Change = .085). IP revealed a good fitting model χ²(4) = 1.15, p = .886, RMSEA = 0.000, CFI = 1.000 after covarying Animals total and FAS total (M.I. = 4.619, Par Change = 9.068). Lastly, GS indicated a good fitting model χ²(8) = 7.22, p = .513, RMSEA = 0.000, CFI = 1.000 after covarying TOH total time and PA (M.I = 4.25, Par Change = -77.868). Therefore, all four constructs were reliable and valid, and the utility of a parsimonious EF battery is suggested. Investigation of the inter-relationships between the constructs using regression techniques, de-emphasises the role of Attentional Control and argue instead for capacity bound skills.

A data-fusion approach to identifying developmental dyslexia from multi-omics datasets

This exploratory study tested and validated the use of data fusion and machine learning techniques to probe high-throughput omics and clinical data with a goal of exploring the etiology of developmental dyslexia. Developmental dyslexia is the leading learning disability in school aged children affecting roughly 5-10% of the US population. The complex biological and neurological phenotype of this life altering disability complicates its diagnosis. Phenome, exome, and metabolome data was collected allowing us to fully explore this system from a behavioral, cellular, and molecular point of view. This study provides a proof of concept showing that data fusion and ensemble learning techniques can outperform traditional machine learning techniques when provided small and complex multi-omics and clinical datasets. Heterogenous stacking classifiers consisting of single-omic experts/models achieved an accuracy of 86%, F1 score of 0.89, and AUC value of 0.83. Ensemble methods also provided a ranked list of important features that suggests exome single nucleotide polymorphisms found in the thalamus and cerebellum could be potential biomarkers for developmental dyslexia and heavily influenced the classification of DD within our machine learning models.

Neuropsychological intervention of dyslexia has a positive effect on aspects of psychological well-being in young adults - a randomized controlled study

Effectiveness of individual- and group-based neuropsychological intervention on aspects of psychological well-being of dyslexic adults was evaluated. Dyslexic young adults (n = 120) were randomly assigned into individual intervention, group intervention or wait-list control group. Both interventions focussed on cognitive strategy learning, supporting self-esteem, and using psychoeducation. In group format peer support was also utilized. Cognitive and behavioural strategies, mood states, quality of life and self-esteem were assessed via self-report questionnaires at baseline, after the intervention/wait-list control time at 5 months and 10 months. Results indicated that the neuropsychological interventions had a positive effect on self-evaluated cognitive and behavioural strategies, especially in increasing success expectations and to a lesser degree in diminishing task-avoidance and in group intervention in diminishing social pessimism. The interventions also improved cognition-related quality of life and, to a lesser degree, self-esteem. These results indicate that structured neuropsychological interventions can positively affect self-evaluated psychological well-being, especially on cognitive and behavioural strategies. Considering the secondary consequences of dyslexia, support among young adults is often needed beyond the cognitive and reading-based challenges dyslexia poses.

Sequential and spatial letter reversals in adults with dyslexia during a word comparison task: demystifying the "was saw" and "db" myths

Whether sequential and spatial letter reversals characterize dyslexia in children has been unclear, largely due to developmental variability of these errors in children with and without dyslexia. Here we demonstrate both types of reversals for the first time in adults with dyslexia (n = 22) but not in control adults (n = 20). Participants evaluated 576 word pairs that consisted of two identical words or two words that differed subtly, by categorizing them as same or different. Two subsets of word pairs differed in sequential (e.g. "two tow") and spatial (e.g. "cob cod") letter reversals. The adults with dyslexia were less accurate than the controls regarding both types of word pairs. Their accuracy during left/right letter reversals was lower, compared to both up/down letter reversals (e.g. "cub cup") and nonsymmetric letter similarities (e.g. "half halt"). Accuracy during left/right reversals was correlated with accuracy during sequential rearrangement in the word pair task as well as with a composite measure of sequential processing based on nonword repetition, nonword reading, and multisyllabic word repetition. It was also correlated with a composite measure of literacy skills. A subset of the dyslexia group who produced left/right errors during a rapid single letter naming task obtained lower accuracy than the dyslexia subgroup without such errors during both types of letter reversals, and their overall literacy skills were lower. We conclude that sequential and left/right letter reversals characterize a severe dyslexia subtype. These two types of reversal are associated, are part of a general deficit in sequential processing likely due to cerebellar deficits, and persist into adulthood.

Both Individual and Group-Based Neuropsychological Interventions of Dyslexia Improve Processing Speed in Young Adults: A Randomized Controlled Study

Effectiveness of individual and group-based neuropsychological interventions on cognitive aspects of dyslexia in young adults was evaluated. Dyslexic adults were randomly assigned into individual intervention (n = 40), group intervention (n = 40), or wait-list control group (n = 40). The interventions focused on cognitive strategy learning, supporting self-esteem, and using psychoeducation. Cognitive performance and symptoms were assessed via psychometric testing and self-report questionnaires at baseline, after the intervention/wait-list control time at 5 months and at 10 months. And, 15 months post intervention long-term status was checked via mailed inquiry. Wait-list control group also received an intervention after the 5-month control period. No significant effects were found in primary self-report outcome measures. Both interventions had a positive effect on a measure of processing speed and attention and the effect remained after the 5-month follow-up period. In self-reported cognitive symptoms, a positive trend was evident in self-reported reading habits. Furthermore, minor self-evaluated benefits reaching up to 15 months post intervention were found. There were no significant differences between the results of individual and group intervention as both interventions improved cognitive performance. The results indicate that a structured neuropsychological intervention could be effective in ameliorating dyslexia-related cognitive symptoms in young adults.

Dyslexia-related impairments in sequence learning predict linguistic abilities

Dyslexia is often characterized by disordered word recognition and spelling, though dysfunction on various non-linguistic tasks suggests a more pervasive deficit may underlie reading and spelling abilities. The serial-order learning impairment in dyslexia (SOLID) hypothesis proposes that sequence learning impairments fundamentally disrupt cognitive abilities, including linguistic processes, among individuals with dyslexia; yet only some studies report sequence learning deficits in people with dyslexia relative to controls. Evidence may be mixed because traditional sequence learning tasks often require strong motor demands, working memory processes and/or executive functions, wherein people with dyslexia can show impairments. Thus, observed sequence learning deficits in dyslexia may only appear to the extent that comorbid motor-based processes, memory capacity, or executive processes are involved. The present study measured sequence learning in college-aged students with and without dyslexia using a single task that evaluates sequencing and non-sequencing components but without strong motor, executive, or memory demands. During sequencing, each additional link in a sequence of stimuli leading to a reward is trained step-by-step, until a complete sequence is acquired. People with dyslexia made significantly more sequencing errors than controls, despite equivalent performance on non-sequencing components. Mediation analyses further revealed that sequence learning accounted for a large portion of the variance between dyslexia status and linguistic abilities, particularly pseudo-word reading. These findings extend the SOLID hypothesis by showing difficulties in the ability to acquire sequences that may play an underlying role in literacy acquisition.

Cognitive predictors of sequential motor impairments in children with dyslexia and/or attention deficit/hyperactivity disorder

This study examined cognitive predictors of sequential motor skills in 215 children with dyslexia and/or attention deficit/hyperactivity disorder (ADHD). Visual working memory and math fluency abilities contributed significantly to performance of sequential motor abilities in children with dyslexia (N = 67), ADHD (N = 66) and those with a comorbid diagnosis (N = 82), generally without differentiation between groups. In addition, primary diagnostic features of each disorder, such as reading and inattention, did not contribute to the variance in motor skill performance of these children. The results support a unifying framework of motor impairment in children with neurodevelopmental disorders such as dyslexia and ADHD.

Comprehension in Proficient Readers: The Nature of Individual Variation

Individual-difference research on reading comprehension is challenging because reader characteristics are as correlated with each other as they are with comprehension. This study was conducted to determine which abilities are central to explaining comprehension and which are secondary to other abilities. A battery of psycholinguistic and cognitive tests was administered to community college and university students. Seven constructs were identified: word decoding, working-memory capacity (WMC), general reasoning, verbal fluency, perceptual speed, inhibition, and language experience. Only general reasoning and language experience had direct effects; these two variables accounted for as much variance in comprehension as did the complete set. Direct effects of WMC and decoding were found only when general reasoning and language experience were deleted from the models. The authors question the need to include WMC in our theories of variability in adult reading comprehension and highlight the need to understand precisely how vocabulary facilitates comprehension.

An exploratory factor analysis of the cognitive functioning of first-year bachelor students with dyslexia

An increasing number of students with dyslexia register in higher education. As a consequence, information on their pattern of strengths and weaknesses is essential to construct adequate assessment and diagnostic protocols. In a sample of 100 first-year bachelor students with dyslexia and 100 control students, a large pool of cognitive skills were tested using a variety of tests. When we applied an exploratory factor analysis to scores, a model with ten factors fitted the data best. Effect sizes were used to express the processing costs of students with dyslexia. The factors related to reading, spelling, flashed orthography, phonology, naming, math, and reading fluency resulted in large effect sizes. A factor combining all measures for crystallized IQ had a medium effect size. The subtests for fluid intelligence were divided in two separate constructs. Relationships between all subtest scores are visualized and interpreted in a general theoretical and practical framework.

Associations among measures of sequential processing in motor and linguistics tasks in adults with and without a family history of childhood apraxia of speech: a replication study

The purpose of this study was to address the hypothesis that childhood apraxia of speech (CAS) is influenced by an underlying deficit in sequential processing that is also expressed in other modalities. In a sample of 21 adults from five multigenerational families, 11 with histories of various familial speech sound disorders, 3 biologically related adults from a family with familial CAS showed motor sequencing deficits in an alternating motor speech task. Compared with the other adults, these three participants showed deficits in tasks requiring high loads of sequential processing, including nonword imitation, nonword reading and spelling. Qualitative error analyses in real word and nonword imitations revealed group differences in phoneme sequencing errors. Motor sequencing ability was correlated with phoneme sequencing errors during real word and nonword imitation, reading and spelling. Correlations were characterized by extremely high scores in one family and extremely low scores in another. Results are consistent with a central deficit in sequential processing in CAS of familial origin.

The genetics of reading disabilities: from phenotypes to candidate genes

This article provides an overview of (a) issues in definition and diagnosis of specific reading disabilities at the behavioral level that may occur in different constellations of developmental and phenotypic profiles (patterns); (b) rapidly expanding research on genetic heterogeneity and gene candidates for dyslexia and other reading disabilities; (c) emerging research on gene-brain relationships; and (d) current understanding of epigenetic mechanisms whereby environmental events may alter behavioral expression of genetic variations. A glossary of genetic terms (denoted by bold font) is provided for readers not familiar with the technical terms.

A multigenerational family study of oral and hand motor sequencing ability provides evidence for a familial speech sound disorder subtype

PURPOSE: To evaluate phenotypic expressions of speech sound disorder (SSD) in multigenerational families with evidence of familial forms of SSD. METHOD: Members of five multigenerational families (N = 36) produced rapid sequences of monosyllables and disyllables and tapped computer keys with repetitive and alternating movements. RESULTS: Measures of repetitive and alternating motor speed were correlated within and between the two motor systems. Repetitive and alternating motor speeds increased in children and decreased in adults as a function of age. In two families with children who had severe speech deficits consistent with disrupted praxis, slowed alternating, but not repetitive, oral movements characterized most of the affected children and adults with a history of SSD, and slowed alternating hand movements were seen in some of the biologically related participants as well. CONCLUSION: Results are consistent with a familial motor-based SSD subtype with incomplete penetrance, motivating new clinical questions about motor-based intervention not only in the oral but also the limb system.