Linda J. Lombardino

Anatomical Risk Factors that Distinguish Dyslexia from SLI Predict Reading Skill in Normal Children.

UNLABELLED These studies investigated whether anatomical measures could separate phonologically-based reading disability (PD) from nonphonologically-based learning disabilities such as specific language impairment (SLI). In a previous study. four brain measures (cerebral asymmetry. summed planum temporale and parietale asymmetry, anterior cerebellar asymmetry, and a duplicated left Heschls gyrus) distinguished a group of PD adults from reading disabled adults without specific phonological deficits (URD). Study 1 found that these measures did not distinguish 14 reading disabled children from 21 children with SLI. Instead, differences were found in cerebral volume, planum temporale asymmetry, and the size of a single left Heschls gyrus. Study 2 demonstrated that including all seven measures in a discriminant analysis separated the adults and children into two groups: one with 100% of the PD adults and 75% of the reading disabled children and the other with 72% of the SLI children and 75% of the URD adults. Study 3 demonstrated that an anatomical risk factor index (ARF7) generated from the discriminant function with seven brain measures predicted reading in normal children. Children with ARF7 near 0 (normal anatomy) had superior verbal ability and phonological decoding scores that improved with age. Normal children with negative ARF7 the relatively s mall symmetrical structures that characterize SLI)had deficits in verbal ability. Children with positive ARF7 (the asymmetrical structures that characterize PD) had phonological decoding scores that decreased with age. These results suggest that PD and SLI are qualitatively different disorders associated with anatomical deviations in opposite directions from the population mean. LEARNING OUTCOMES As a result of this activity, the participant will be able to: (1) distinguish the neuroanatomical features that characterize PD and SLI; (2) recognize that PD is associated with large asymmetrical brain structures while SLI is associated with smaller symmetrical brain structures; (3) understand that children with moderate sized brains and whose anatomy is intermediate between symmetry and extreme asymmetry have an enhanced probability of developing good verbal ability; (4) understand that reading disabilities depend on the interaction of neurodevelopment and the environment.

Planar Asymmetry Tips the Phonological Playground and Environment Raises the Bar.

Reading readiness varies as a function of family and environmental variables. This study of 11-year-old children (N = 39) was designed to determine if there was an additional or interactive contribution of brain structure. Evidence is presented that both environmental and biological variables predict phonological development. Temporal lobe (planar) asymmetry, hand preference, family history of reading disability, and SES explained over half of the variance in phonological and verbal performance. The results demonstrate a linear association between cerebral organization and phonological skill within socioeconomic groups. These data provide concrete evidence to support the commonly held assumption that both environmental and biological factors are independent determinants of a childs ability to process linguistic information.

Comorbid auditory processing disorder in developmental dyslexia

Objective The primary objective of this study was to investigate the extent of comorbid auditory processing disorder (APD) in a group of adults with developmental dyslexia. An additional objective was to compare performance on auditory tasks to results from standardized tests of reading in an attempt to generate a clinically useful profile of developmental dyslexics with comorbid APD. Design A group of eleven persons with developmental dyslexia and 14 age- and intelligence-matched controls participated in the study. Behavioral audiograms, 226-Hz tympanograms, and word recognition scores were obtained binaurally from all subjects. Both groups were administered the frequency-pattern test (FPT) and duration-pattern test (DPT) monaurally (30 items per ear) in both the left and right ear. Gap detection results were obtained in both groups (binaural presentation) using narrowband noise centered at 1 kHz in an adaptive two-alternative forced-choice (2-AFC) paradigm. The FPT, DPT, and gap detection results were analyzed for interaural (where applicable), intergroup, and intragroup differences. Correlations between performance on the auditory tasks and the standardized tests of reading were examined. Additive logistic regression models were fit to the data to determine which auditory tests proved to be the best predictors of group membership. Results The persons with developmental dyslexia as a group performed significantly poorer than controls on both the FPT and DPT. Furthermore, the group differences were significant in both monaural conditions. On the FPT and DPT, five of the eleven participants with dyslexia performed below the widely used clinical criterion for APD of 70% correct in either ear. All five of these participants performed below criterion on the FPT, whereas four of the five additionally performed below 70% on the DPT. The data also were analyzed by fitting a series of stepwise logistic regression models, which indicated that gap detection did not significantly predict group membership, whereas the FPT and DPT were significant predictors. The addition of the FPT score after the DPT did not result in a significant change in the residual deviance. Conclusions Approximately half of the participants with developmental dyslexia showed clinically significant diminished performance on the FPT and DPT indicative of APD. These results indicate that the percentage of persons with developmental dyslexia and comorbid APD may be substantial enough to warrant serious clinical considerations.

Linguistic Deficits in Children With Reading Disabilities

Although recent research into the nature of linguistic abilities and disabilities in children with developmental reading disorders points to phonological processing difficulties as the core deficit...

Sentence comprehension in young adults with developmental dyslexia

This study investigated the effects of syntactic complexity on written sentence comprehension in compensated adults with dyslexia. Because working memory (WM) plays a key role in processing complex sentences, and individuals with dyslexia often demonstrate persistent deficits in WM, we hypothesized that individuals with dyslexia would perform more poorly on tasks designed to assess the comprehension of syntactic structures that are especially taxing on WM (e.g., passives, sentences with relative clauses). Compared to their nondyslexic peers, individuals with dyslexia were significantly less accurate and marginally slower on passive sentences. For sentences containing relative clauses, the dyslexic group was also less accurate but did not differ in response times. Covarying WM and word reading in both analyses eliminated group differences showing that syntactic deficits in adults with dyslexia are constrained by both WM and word-reading ability. These findings support previous research showing that syntactic processing deficits are characteristic of dyslexia, even among high-achieving students.

Subtyping of children with developmental dyslexia via bootstrap aggregated clustering and the gap statistic: comparison with the double-deficit hypothesis

BACKGROUND The marked degree of heterogeneity in persons with developmental dyslexia has motivated the investigation of possible subtypes. Attempts have proceeded both from theoretical models of reading and the application of unsupervised learning (clustering) methods. Previous cluster analyses of data obtained from persons with reading disabilities have suffered from the inherent limitations of unsupervised learning methods. Specifically, the reliability and stability of cluster solutions have proven difficult to determine. Recent developments in the clustering literature have addressed these concerns by permitting checks on the internal validity of the solution. Resampling methods produce consistent groupings of the data independent of initialization effects, while the gap statistic provides a confidence measure for the determination of the optimal number of clusters present in the data. Combining these methods produces a robust data-driven classification that can be compared with theoretically based subtypes to produce better-informed models of developmental dyslexia. AIMS The present study is a novel application of resampling (bootstrap aggregating or bagging) methods and the gap statistic to the subtyping of children with developmental dyslexia. The specific aims of this study are: (1) to illustrate the use of bagging methods and the gap statistic in multivariate data obtained from children with developmental dyslexia; and (2) to compare the bagged clustering thresholded by the gap statistic against the predictions of the double-deficit hypothesis. The double-deficit hypothesis is a prominent theoretical model of developmental dyslexia, which predicts three subtypes: phonological, rate, and phonological-rate impaired readers. METHODS & PROCEDURES Three simulated data sets with known cluster structure were created to check the validity and illustrate the utility of the bagged clustering with the gap statistic in data with known structure. Subsequently, a clinical database of standardized test data (eight tests) from 93 children with developmental dyslexia was clustered using these methods. This procedure was repeated on a database of 93 children without reading disability matched for gender and age as a control. Finally, the clustering was repeated on the entire database of 186 participants. Cluster solutions were obtained for an increasing number of clusters (1-10) and were tested against the null hypothesis that no subtypes were present, i.e. the data represented a single cluster. OUTCOMES & RESULTS Four clusters were identified in the children with developmental dyslexia. There was no evidence of significant cluster structure in the children without dyslexia. Two clusters were identified when children with and without reading impairments were considered together. Among the participants with developmental dyslexia, there was evidence of a phonological-deficit cluster, a rapid-naming cluster, and a cluster showing both depressed phonological processing and rapid naming. These accounted for 73 of the 93 participants (78%). All three are predicted by the double-deficit hypothesis. The fourth cluster consisted of children with normal phonological and rapid naming ability incommensurate with their high verbal ability. An analysis of variance with post-hoc multiple comparisons demonstrated that the phonological, rapid-naming, and double deficit clusters did not differ significantly in age, but the fourth cluster was comprised of significantly older children. The mixed data set revealed two clusters. One cluster consisted almost entirely of the double-deficit and phonological subtypes. The other consisted of the participants without dyslexia and the children with dyslexia demonstrating either a single rapid naming deficit or standardized test scores in the normal range. A silhouette analysis indicated that the four-cluster solution for the children with developmental dyslexia was superior to the two-cluster solution obtained for the entire data set. CONCLUSIONS The study provides support for the presence of distinct subtypes in children with developmental dyslexia and for the double-deficit hypothesis. Specifically, this study finds three subtypes predicted by the double-deficit hypothesis without the assumption of an a priori theoretical model of reading. Taken together, these subtypes account for 79% of the participants with dyslexia. Further, the percentages of children in each subtype are in good agreement with previous studies. The participants in the subtype not predicted by the double-deficit hypothesis were significantly older than the other three groups. Recent advances in unsupervised learning can be expected to aid the improvement and refinement of the definition of developmental dyslexia. If reliable and consistent subtypes can be identified among persons with developmental dyslexia, it is reasonable to assume that diagnostic and intervention efforts will be greatly improved.

Manual and automated measures of superior temporal gyrus asymmetry: concordant structural predictors of verbal ability in children.

The planum temporale is a region on the posterior surface of the temporal lobe that exhibits robust leftward structural asymmetry, which has been linked to verbal ability in children and adults. Traditionally, structural asymmetry has been quantified with manual assessment of high resolution MRI scans. Such measures require subjective and frequently unreliable determination of highly variable anatomical boundaries. Methodological developments in automated image processing (voxel-based morphometry - VBM) offer the opportunity to obtain objective and reliable measures of structural variation. This study examined the extent to which a VBM measure of gray matter asymmetry in the posterior superior temporal gyrus (pSTG) characterized the same individual variation as a manual measure of planum temporale asymmetry in 99 healthy adults and 39 typically developing children. Planum temporale asymmetry was significantly correlated with pSTG gray matter asymmetry in the samples of adults and children. As a measure of validity we examined the extent to which the VBM measure of pSTG gray matter asymmetry predicted measures of verbal ability that were associated with the manual measure of planum temporale asymmetry in the same children. The two asymmetry measures predicted the same variance in verbal ability. The automated measure of pSTG gray matter asymmetry predicted additional significant variance in verbal ability, however. In addition, a posterior STS region was also identified that significantly predicted verbal ability. These results demonstrate significant advantages of an automated voxel-based measure over a manual measure of planum temporale asymmetry.

Effects of phonemic awareness instruction on the encoding skills of children with severe speech impairment

Purpose: To examine the effects of phoneme-grapheme correspondence and phonemic awareness instruction on the encoding abilities of three pre-reading children with severe speech impairment (SSI). Method: Using a single subject multiple baseline design across behaviours and participants, children received phoneme-grapheme awareness instruction followed by instruction in segmenting, manipulating, and encoding consonant-vowel-consonant (CVC) pseudowords. Results: Generalization occurred to encoding of novel CVC pseudo- and real words for two of the three participants. Conclusions: Results suggest that phoneme-grapheme correspondence and phonemic awareness instruction is effective in developing encoding skills in children with SSI. Findings are consistent with those for other at-risk children.

Phonology Matters: A Comprehensive Investigation of Reading and Spelling Skills of School-Age Children With Mild to Moderate Sensorineural Hearing Loss

The investigators measured 7 literacy skills in a group of 21 school-age children with mild to moderate sensorineural hearing loss (MSNH group), and compared the scores to those of 2 age-matched groups: children with dyslexia (DYS group) and, as a control, typically developing hearing children (CA group). The MSNH group performed consistently below the CA group but better than the DYS group, an indication that differences in the groups’ phonological processing profiles might be an important discriminating feature. Interestingly, the MSNH group showed a selective impairment in word reading accuracy only, whereas their reading rate was relatively unaffected. Children with MSNH who show weak phonological awareness skills seem to compensate by relying on orthographic recognition associated with rapid naming ability. To determine which children with MSNH are at high risk for depressed reading achievement, testing across a wide range of literacy skills should be considered.

Reading disabilities, comorbid psychopathology, and the specificity of neurolinguistic deficits

Research on children with learning disabilities, and reading disabilities in particular, indicates a high comorbidity with both internalizing and externalizing disorders. In the first study, a group of children with reading disability (RD, N = 17) was compared with a group of children with RD and co‐occurring psychopathology (RD+, N = 17) on a number of neuropsychological measures. Group comparisons did not reveal any significant differences. The second study investigated the performance of subjects with significant reading disability (RD/RD+, N= 16) as compared to subjects with attention deficit hyperactivity disorder (N = 18) on a number of neurolinguistic and phonological measures. Group comparisons revealed the RD group to have relative deficits in phonological coding, expressive language, elision, and vocabulary. The results of these studies revealed that regardless of the presence of co‐occurring psychopathology, children with RD suffer deficits in neurolinguistic abilities, particularly those relat...