G. Reid Lyon

Disruption of posterior brain systems for reading in children with developmental dyslexia.

BACKGROUND Converging evidence indicates a functional disruption in the neural systems for reading in adults with dyslexia. We examined brain activation patterns in dyslexic and nonimpaired children during pseudoword and real-word reading tasks that required phonologic analysis (i.e., tapped the problems experienced by dyslexic children in sounding out words). METHODS We used functional magnetic resonance imaging (fMRI) to study 144 right-handed children, 70 dyslexic readers, and 74 nonimpaired readers as they read pseudowords and real words. RESULTS Children with dyslexia demonstrated a disruption in neural systems for reading involving posterior brain regions, including parietotemporal sites and sites in the occipitotemporal area. Reading skill was positively correlated with the magnitude of activation in the left occipitotemporal region. Activation in the left and right inferior frontal gyri was greater in older compared with younger dyslexic children. CONCLUSIONS These findings provide neurobiological evidence of an underlying disruption in the neural systems for reading in children with dyslexia and indicate that it is evident at a young age. The locus of the disruption places childhood dyslexia within the same neurobiological framework as dyslexia, and acquired alexia, occurring in adults.

Development of left occipitotemporal systems for skilled reading in children after a phonologically- based intervention

BACKGROUND A range of neurobiological investigations shows a failure of left hemisphere posterior brain systems to function properly during reading in children and adults with reading disabilities. Such evidence of a disruption in the normal reading pathways provides a neurobiological target for reading interventions. In this study, we hypothesized that the provision of an evidence-based, phonologically mediated reading intervention would improve reading fluency and the development of the fast-paced occipitotemporal systems serving skilled reading. METHODS Functional magnetic resonance imaging was used to study the effects of a phonologically based reading intervention on brain organization and reading fluency in 77 children aged 6.1-9.4 years (49 with reading disability and 28 control subjects). Children comprised three experimental groups: experimental intervention (n = 37), community intervention (n = 12), and community control subjects (n = 28). RESULTS Immediately after the year-long intervention, children taught with the experimental intervention had made significant gains in reading fluency and demonstrated increased activation in left hemisphere regions, including the inferior frontal gyrus and the middle temporal gyrus; 1 year after the experimental intervention had ended these children were activating bilateral inferior frontal gyri and left superior temporal and occipitotemporal regions. CONCLUSIONS These data indicate that the nature of the remedial educational intervention is critical to successful outcomes in children with reading disabilities and that the use of an evidence-based phonologic reading intervention facilitates the development of those fast-paced neural systems that underlie skilled reading.

Toward a definition of dyslexia.

A precise and inclusionary definition of dyslexia is sorely needed for at least three reasons. First, accurate identification of dyslexia requires that the key symptoms and characteristics be specified. Second, treatment of dyslexia, including early intervention and general teaching methods, must be based on an informed understanding of what difficulties impede reading develop ment and reading mastery for children and adults with reading disabilities. Third, an operational definition is essential for research purposes. More specifically, to investigate the causes and consequences of dyslexia, to examine whether there are different types of reading problems, and to explore how dys lexia relates to other disorders, it is crucial to study individuals who meet well-specified selection criteria. A number of recent papers and books address, in detail, this need for an opera tional and inclusionary definition of dyslexia and are recom mended for those who wish to pursue more in-depth reviews of the definitional issues in dyslexia (Fletcher and Morris 1986; Lyon and Moats 1993; Lyon et al. 1993; Morris 1988, 1993; Morris, Lyon, Alexander et al. 1994; Shaywitz, Shaywitz, Liberman et al. 1991).

Subtypes of Reading Disability: Variability around a Phonological Core.

Eight measures of cognitive and language functions in 232 children were subjected to multiple methods of cluster analysis in an effort to identify subtypes of reading disability. Clustering yielded 9 reliable subtypes representing 90% of the sample, including 2 nondisabled subtypes, and 7 reading-disabled subtypes. Of the reading-disabled subtypes, 2 were globally deficient in language skills, whereas 4 of the 5 specific reading-disabled subtypes displayed a relative weakness in phonological awareness and variations in rapid serial naming and verbal short-term memory. The remaining disabled subtype was impaired on verbal and nonverbal measures associated with rate of processing, including rate and accuracy of oral reading. Studies showed evidence for discriminative validity among the 7 reading-disabled subtypes. Results support the view that children with reading disability usually display impairments on phonological awareness measures, with discriminative variability on other measures involving phonological processing, language, and cognitive skills.

Neural systems for compensation and persistence: Young adult outcome of childhood reading disability

BACKGROUND This study examined whether and how two groups of young adults who were poor readers as children (a relatively compensated group and a group with persistent reading difficulties) differed from nonimpaired readers and if there were any factors distinguishing the compensated from persistently poor readers that might account for their different outcomes. METHODS Using functional magnetic resonance imaging, we studied three groups of young adults, ages 18.5-22.5 years, as they read pseudowords and real words: 1) persistently poor readers (PPR; n = 24); 2) accuracy improved (compensated) readers (AIR; n = 19); and 3) nonimpaired readers (NI, n = 27). RESULTS Compensated readers, who are accurate but not fluent, demonstrate a relative underactivation in posterior neural systems for reading located in left parietotemporal and occipitotemporal regions. Persistently poor readers, who are both not fluent and less accurate, activate posterior reading systems but engage them differently from nonimpaired readers, appearing to rely more on memory-based rather than analytic word identification strategies. CONCLUSIONS These findings of divergent neural outcomes as young adults are both new and unexpected and suggest a neural basis for reading outcomes of compensation and persistence in adults with childhood dyslexia.

Validity of IQ-Discrepancy Classifications of Reading Disabilities: A Meta-Analysis

According to federal regulations, children with reading difficulties are eligible for special education services under the learning disability category if they display reading skills that are significantly lower than their scores on intelligence (IQ) tests. Children who are poor readers but do not display this discrepancy are not eligible for special education. A meta-analysis involving 46 studies addressing the validity of this classification of poor readers revealed substantial overlap between the IQ-discrepant and IQ-consistent poor readers. Aggregated effect sizes were in the negligible range for the Behavior (–.05) and Achievement (–.12) domains but in the small range for the Cognitive Ability domain (.30). The latter effects were heterogeneous, with larger estimates showing higher performance by the IQ-discrepant poor readers. The size of the effects could be largely explained by the selection criteria used to form groups, indicating that variation in group definitions across studies accounted for variability in effect size estimates. These results provide little evidence supporting the validity of the IQ-discrepancy classification fundamental to public policy concerning students with learning disabilities and cast doubt on the need for IQ tests in identifying these students.

Psychometric Approaches to the Identification of LD IQ and Achievement Scores Are Not Sufficient

Simulated data were used to demonstrate that groups formed by imposing cut-points based on either discrepancy or low-achievement definitions of learning disabilities (LD) are unstable over time. Similar problems were demonstrated in longitudinal data from the Connecticut Longitudinal Study, where 39% of the children designated as having LD in Grade 3 changed group placement with repeated testing in Grade 5. These results show that the practice of subdividing a normal distribution with arbitrary cut-points leads to instability in group membership. Approaches to the identification of children as having LD based solely on individual test scores not linked to specific behavioral criteria lead to invalid decisions about individual children. Low-achievement definitions are not a viable alternative to IQ-discrepancy definitions in the absence of other criteria, such as the traditional exclusions and response to quality intervention. If we accept the premise of multiple classes of low achievers, then we must develop identification systems that are valid and abandon systems whose only merits are their historical precedence and convenience.

Evidence-based assessment of learning disabilities in children and adolescents.

The reliability and validity of 4 approaches to the assessment of children and adolescents with learning disabilities (LD) are reviewed, including models based on (a) aptitude-achievement discrepancies, (b) low achievement, (c) intra-individual differences, and (d) response to intervention (RTI). We identify serious psychometric problems that affect the reliability of models based on aptitude-achievement discrepancies and low achievement. There are also significant validity problems for models based on aptitude-achievement discrepancies and intra-individual differences. Models that incorporate RTI have considerable potential for addressing both the reliability and validity issues but cannot represent the sole criterion for LD identification. We suggest that models incorporating both low achievement and RTI concepts have the strongest evidence base and the most direct relation to treatment. The assessment of children for LD must reflect a stronger underlying classification that takes into account relations with other childhood disorders as well as the reliability and validity of the underlying classification and resultant assessment and identification system. The implications of this type of model for clinical assessments of children for whom LD is a concern are discussed.

The Role of Functional Magnetic Resonance Imaging in Understanding Reading and Dyslexia

Converging evidence from a number of lines of investigation indicates that dyslexia represents a disorder within the language system and more specifically within a particular subcomponent of that system, phonological processing. Recent advances in imaging technology, particularly the development of functional magnetic resonance imaging (fMRI), provide evidence of a neurobiological signature for dyslexia, specifically a disruption of 2 left hemisphere posterior brain systems, 1 parietal-temporal, the other occipital-temporal, with compensatory engagement of anterior systems around the inferior frontal gyrus and a posterior (right occipital-temporal) system. Furthermore, good evidence indicates a computational role for the left occipital-temporal system: the development of fluent (automatic) reading. In addition, fMRI studies of young adults with reading difficulties followed prospectively and longitudinally from age 5 through their mid 20s suggests that there may be 2 types of reading difficulties, 1 primarily reflecting a genetic basis, the other, and far more common, reflecting environmental influences. The brain systems for reading are malleable and their disruption in children with dyslexia may be remediated by provision of an evidence-based, effective reading intervention. These studies offer the promise for more precise identification and effective management of dyslexia in children, adolescents, and adults.

Teacher Knowledge, Instructional Expertise, and the Development of Reading Proficiency

Teacher knowledge and instructional expertise have been found in correlational and pre- and posttest studies to be related to student reading achievement. This article summarizes data presented in this special issue and additional research to address four questions: (a) What do expert reading teachers know? (b) Why do teachers need to acquire this knowledge? (c) Do teachers believe they have this knowledge? and (d) Are teachers being adequately prepared to teach reading? Well-designed studies relevant to this topic have been sparse with a noticeable lack of attention given to identifying specific causal links between teacher knowledge, teaching expertise, and student reading achievement. Until the appropriate research designs and methodologies are applied to address the question of causal effects, conclusions about the specific content that teachers must know and the instructional practices that are most beneficial in presenting this content are preliminary at best. Future studies of the effect of essential reading content knowledge must be extended beyond word-level skills to vocabulary, reading comprehension, and writing.