Developmental dyscalculia and basic numerical capacities: a study of 8-9-year-old students

Thirty-one 8- and 9-year-old children selected for dyscalculia, reading difficulties or both, were compared to controls on a range of basic number processing tasks. Children with dyscalculia only had impaired performance on the tasks despite high-average performance on tests of IQ, vocabulary and working memory tasks. Children with reading disability were mildly impaired only on tasks that involved articulation, while children with both disorders showed a pattern of numerical disability similar to that of the dyscalculic group, with no special features consequent on their reading or language deficits. We conclude that dyscalculia is the result of specific disabilities in basic numerical processing, rather than the consequence of deficits in other cognitive abilities.     

Visual discrimination deficits of reading-disabled children: Sex artifact?

Several theorists have suggested that deficits in visual discrimination play an etiological role in the development of reading deficits in children who are diagnosed as learning-disabled. Supporting this theory, a number of studies have shown that disabled readers make more errors on visual discrimination tasks than do good readers. The present study, however, suggests that those findings may have been due to a sex-difference artifact. Thirty-six 8- and 9-year-old good readers and reading-disabled children of both sexes responded to 40 matching items under untimed conditions. Males made more errors than females, but overall, reading-disabled children made no more errors than good readers. These findings, along with a reanalysis of previous studies, suggest that because reading disabilities are more common in males, evidence construed as supporting a visual discrimination hypothesis may have been an artifact of a sex difference in studies in which sex was not controlled.     

Connections between reading disability and behavior problems: Testing temporal and causal hypotheses

In this study of children's reading and behavior problem status from Grade 2 to Grade 4 of elementary school, we tested hypotheses concerned with the temporal and causal connections between these two closely associated disorders. Children with both, either, or neither kinds of problems were followed up over 2 years. While reading disability remained stable over time, there was greater variability in behavior problem status. Our data did not support the claim that reading problems lead to the development of behavior problems. Children who were comorbid had the worst outcome at follow-up, suggesting that behavior problems may exacerbate reading delay. Reading-disabled children were lower (albeit in the normal range) on intelligence, but when IQ was controlled, large group differences on reading and spelling were still evident. Attention deficit hyperactivity disorder (ADHD) type behavior problems significantly differentiated children with comorbid problems from children with behavior problems alone. Sex differences were noted in the association, with two-thirds of reading-disabled boys also having behavior problems and two-thirds of reading-disabled girls having no behavior problems, suggesting that pathways to reading disability may be gender specific.This research was supported by a grant from the Australian Research Council. Our thanks to the children, families and teachers for their support of our project.     

Multifactorial assessment of reading disability: identifying the best predictors

A multifactorial diagnostic assessment battery was evaluated using data obtained from 105 reading-disabled children and their matched controls (total N = 210). A stepwise discriminant function analysis selected five nonreading measures from among 16 as the best diagnostic predictors of reading disability. These measures included WISC-R Information and Digit Span, self-reported family histories of reading problems, and tests of symbol-processing speed and letter fluency.     

Sustained attention in normal and in reading-disabled youngsters with and without ADDH

Three groups of children — one normal, one reading-disabled, and one reading-disabled with an additional diagnosis of attention deficit disorder with hyperactivity (ADDH)-were administered the Continuous Performance Test and compared on correct detections and three types of commission errors. All three groups showed a decline in sustained attention over the course of the task but not differentially according to diagnostic group. When younger and older subgroups were compared, the reading-disabled children were found to make significantly more correct detections with increased age, but not when the reading disability was accompanied by ADDH. The latter group of children also were differentiated by a type of commission error, previously associated with impulsive responding, that remained prominent in the older subgroup of dually diagnosed children. Reading-disabled children were differentiated by a second type of commission error which possibly was associated with inattention or short-term memory deficit and which diminished with age.The author would like to thank the staff of St. Patricks School and in particular its principal Sister Patrick Mary for her able administrative support of the study. The author would also like to thank the administration and staff of the Unitas Clinic for their cooperation.     

Cerebellar tasks do not distinguish between children with developmental dyslexia and children with intellectual disability.

This paper explored the claim that only children with developmental dyslexia, whose reading ability is discrepant from their average general reasoning ability show specific deficits in motor tasks assessing cerebellar functioning (Fawcett et al., 2001, Cerebellar tests differentiate between groups of poor readers with and without IQ discrepancy. J. Learning Disabilities, 34, 119) and rapid serial naming (RAN, Wolf & Bowers, 1999, The double deficit hypothesis for the developmental dyslexias. J. Educ. Psychol., 91, 1). All available children between the ages of 11 and 14 were recruited from two special schools for children with either (a) formally-diagnosed intellectual disabilities (N = 18); or (b) formal diagnoses of developmental dyslexia (N = 25). These two groups of children did not differ on gender, age, pseudoword decoding abilities, or on 7 of 8 literacy measures, but did differ significantly, as expected on verbal and non-verbal reasoning tasks. Importantly, there were no deficits in bead threading ability or postural stability in the children with developmental dyslexia compared to the children with intellectual disabilities. There were also no between-group differences in rapid naming measures. The present results therefore provide no support for the claim that cerebellar deficits or RAN distinguish between children with dyslexia and children with intellectual disabilities that include reading.     

Inhibition and shifting in children with learning deficits in arithmetic and reading

The executive functions of inhibition and shifting were studied in arithmetic-disabled children, reading-disabled children, reading plus arithmetic-disabled children, and controls (N = 74). Measures involved the rapid naming of objects, digits, letters, or quantities with or without additional task requirements that reflected inhibition or shifting. Also, the Making Trails task, reflecting shifting, was administered. For tasks without executive demands, arithmetic-disabled children were slower in the naming of digits and quantities, whereas reading-disabled children were slower in the naming of digits and letters. For the executive tasks, arithmetic-disabled children as well as reading plus arithmetic-disabled children were impaired on the Making Trails task and on an object naming task that required both inhibition and shifting. Reading-disabled children exhibited no problems in executive functioning. Furthermore, it was shown that reading plus arithmetic-disabled children experienced the combination of problems that characterize children with a single learning deficit.     

Numerical and arithmetical cognition: patterns of functions and deficits in children at risk for a mathematical disability.

Based on performance on standard achievement tests, first-grade children (mean age = 82 months) with IQ scores in the low-average to high-average range were classified as at risk for a learning disability (LD) in mathematics, reading, or both. These at-risk children (n = 55) and a control group of academically normal peers (n = 35) were administered experimental tasks that assessed number comprehension and production skills, counting knowledge, arithmetic skills, working memory, and ease of retrieving information from long-term memory. Different patterns of intact cognitive functions and deficits were found for children in the different at-risk groups. As a set, performance on the experimental tasks accounted for roughly 50% and 10% of the group differences in mathematics and reading achievement, respectively, above and beyond the influence of IQ. Performance on the experimental tasks thus provides insights into the cognitive deficits underlying different forms of LD, as well as into the sources of individual differences in academic achievement.     

发展性阅读障碍亚类型研究进展

发展性阅读障碍是一种特殊的学习障碍,伴有多种认知缺陷并且存在不同的亚类型。依据相关的阅读模型理论,阅读障碍可划分为语音型和表层型。从认知缺陷角度出发,语音加工缺陷是主要的缺陷表现,以此为特征形成一种主要的阅读障碍的亚类型,同时还有以正字法加工缺陷和快速命名缺陷为主的其他亚类型。而以基本感知觉缺陷为标准,主要有以视觉加工缺陷和以听觉加工缺陷为主的两种亚类型。在汉语条件下,依据同样的阅读模型理论,语音型阅读障碍亚类型比例明显低于拼音文字条件下的。汉语阅读障碍也具有分别以语音加工缺陷、快速命名缺陷和正字法加工缺陷为主要认知缺陷的亚类型。未来有必要从神经机制角度进一步明确不同亚类型的神经基础。     

Performance of disabled and normal readers on the continuous performance test

Twelve-year-old reading-disabled children of normal intelligence were compared on the Continuous Performance Test with two control groups of normal intelligence and reading ability either of the same age or of the same reading age as the reading-disabled group. Signal-detection analysis showed that the reading-disabled were more conservative than chronological-age controls in their willingness to identify the target letter sequence. Although this conservative performance was shared by the reading-age controls, the readingdisabled suffered an additional handicap of relatively frequent anticipatory errors. Groups also differed on a sensitivity measure, suggesting a deficit in working memory in the reading-disabled children.This research was supported by the New Zealand Neurological Foundation. We thank the children and school staff for their willing cooperation. We are indebted to the research students who found the subjects and helped collect the data.     

Reading-disabled hyperactive children: A distinct subgroup of Attention Deficit Disorder with Hyperactivity?

Mixed hyperactive/reading-disabled children, selected from a large sample of hyperactive children, were compared to pure hyperactive children on demographic, behavioral, and neuropsychological measures. Children in the Mixed group were reading-disabled relative to age and IQ; those in the Pure group had achievement scores that were average relative to age and IQ. The Mixed group was significantly older than the Pure group; there were no differences in gender, race, or socioeconomic status. Behaviorally, the groups did not differ significantly on teacher ratings or on psychiatric ratings of aggression. The Mixed group had a significantly higher Performance IQ, whereas the Pure group had a significantly higher Verbal IQ and performed better on measures of cognitive impulsivity. Several other measures failed to distinguish the groups. The data give minimal support to the notion that pure hyperactive and mixed hyperative/reading-disabled children constitute distinct subgroups of Attention Deficit Disorder with Hyperactivity.This research was supported in part by Mental Health Clinical Research Grant MH-30906 and by U. S. Public Health Service Grant MH-18579.     

The impact of developmental speech and language impairments on the acquisition of literacy skills

Children with developmental speech/language impairments are at higher risk for reading disability than typical peers with no history of speech/language impairment. This article reviews the literacy outcomes of children with speech/language impairments, clarifying the differential risk for three groups of children: speech production impairments alone, oral language impairments alone, and speech production and oral language impairments. Children at greatest risk for reading and writing disabilities are children with language impairments alone and children with comorbid speech impairments and language impairments. For children with speech impairments alone, there is limited risk for literacy difficulties. However, even when reading skills are within the average range, children with speech impairments may have difficulties in spelling. Children with language impairments are likely to display reading deficits in word decoding and reading comprehension. It is not clear what role early literacy interventions play in the amelioration of reading difficulties in these populations.     

A comparison of componential and traditional approaches to training reading skills

Primary school children with average intelligence and no oral language comprehension deficits—but who were 18 or more months behind their peers in reading comprehension—served as subjects in an evaluation of two approaches to reading remediation. Half the children received teacher-based tutoring using the DISTAR programme (Science Research Associates, 1983). The remaining students received practice on four computer games. These games were designed to improve performance on a set of information-processing components shown in previous research to have an important impact on reading comprehension. Training in both conditions focused mainly on word decoding and phonics. Although almost all students improved their reading comprehension test scores after training, the poorest readers made significantly greater gains in the componential training condition than in the DISTAR condition. These results demonstrate the effectiveness of the componential approach with a sample of specifically reading-disabled children. They also show that componential training can be a practical adjunct to a traditional tutoring programme.     

Functional cerebral lateralization in subtypes of disabled readers

This study investigated the functional cortical organization of reading-disabled boys and age-matched normal readers. Subjects were initially classified according to E. Boder's (1971a. In B. Bateman (Ed.), Learning disorders. Seattle: Special Child Publications. Vol. 4.) distinction between dysphonetic children (who make nonphonetic, bizarre spelling errors), dyseidetic children (who make phonetically acceptable errors, but do not respond to some words as “wholes”), and children who display normal error patterns (who make phonetically acceptable errors and respond to words as “wholes”). It was hypothesized that different types of reading disability would be associated with different patterns of lateralized brain function. This proposal was examined by testing subjects on three experimental neuropsychological measures—hemispheric time-sharing, conjugate lateral eye movements, and tactile directional perception. Conjugate lateral eye movements were disregarded as the control subjects failed to show predicted asymmetries on this measure. The two other measures were considered valid and demonstrated atypical lateralization in the reading-disabled groups. Lateralization of verbal and/or spatial functiosn differed among the reading-disabled groups and an attempt was made to relate these atypical patterns to the type of reading difficulties presented.     

Individual prediction of dyslexia by single versus multiple deficit models

The overall goals of this study were to test single versus multiple cognitive deficit models of dyslexia (reading disability) at the level of individual cases and to determine the clinical utility of these models for prediction and diagnosis of dyslexia. To accomplish these goals, we tested five cognitive models of dyslexia--two single-deficit models, two multiple-deficit models, and one hybrid model--in two large population-based samples, one cross-sectional (Colorado Learning Disability Research Center) and one longitudinal (International longitudinal Twin Study). The cognitive deficits included in these cognitive models were in phonological awareness, language skill, and processing speed and/or naming speed. To determine whether an individual case fit one of these models, we used two methods: 1) the presence or absence of the predicted cognitive deficits, and 2) whether the individual's level of reading skill best fit the regression equation with the relevant cognitive predictors (i.e., whether their reading skill was proportional to those cognitive predictors.) We found that roughly equal proportions of cases met both tests of model fit for the multiple deficit models (30-36%) and single deficit models (24-28%); hence, the hybrid model provided the best overall fit to the data. The remaining roughly 40% of cases in each sample lacked the deficit or deficits that corresponded with their best-fitting regression model. We discuss the clinical implications of these results for both diagnosis of school-age children and preschool prediction of children at risk for dyslexia.     

Short-term serial recall in ADDH,normal, and reading-disabled boys

Short-term retention of verbal items of span and subspan length was examined in hyperactive (ADDH), normal and non-ADDH reading-disabled boys. Performance of ADDH and normal boys did not differ on three measures of verbal serial recall. Thus, it appears that the cognitive deficits of ADDH children cannot be attributed to deficient retention of stimuli. In contrast, reading-disabled (RD) boys performed significantly more poorly than both normal and ADDH boys when required to recall verbal items following filled delay intervals in which the children were required to perform a competing verbal activity. The results suggest that verbal encoding of RD children is particularly vulnerable to interference from other verbal stimuli. ADDH and RD children may represent subsamples of children demonstrating academic difficulties, with each group showing a characteristic pattern of cognitive deficits.This article is based on a doctoral dissertation submitted to the Faculty of Graduate Studies and Research of McGill University. Special thanks are due to Rhonda Amsel for her help and advice.     

Processing Speed Deficits in Attention Deficit/Hyperactivity Disorder and Reading Disability

The goal of the current study was to test whether deficits in processing speed (PS) may be a shared cognitive risk factor in reading disability (RD) and Attention Deficit/Hyperactivity Disorder (ADHD), which are known to be comorbid. Literature on ADHD and RD suggests that deficits on tasks with a speeded component are seen in both of these disorders individually. The current study examined a wide range of speeded tasks in RD, ADHD, comorbid RD+ADHD, and a control group to test whether RD and ADHD have similar profiles of PS deficits, and whether these deficits are shared by the two disorders. The results suggest that a general PS deficit exists in both clinical groups compared to controls, although children with RD demonstrate greater PS deficits than children with ADHD. Two tests (underadditivity and partial correlations) were conducted to test whether these PS deficits are shared. Since we found that PS deficits were underadditive in the comorbid group and that partialling PS reduced the correlation between RD and ADHD, it appears that PS is a shared cognitive risk factor that may help explain the comorbidity of these two disorders.     

Reading disability: A problem in rule learning and word decoding

Traditional explanations of reading disability (e.g., perceptual, memory, and phonetic receding deficits) have encountered logical difficulties and substantial empirical disconfirmation. An alternative conceptualization of the nature of reading disability is proposed. Disabled readers are hypothesized to suffer a fundamental problem in acquiring word knowledge and word processing skills. Poor decoding skills prevent them from developing sophisticated reading comprehension skills. From this perspective, the cognitive deficits of disabled readers result from failure to acquire and generalize complex processing skills originally mastered through reading experience. Recent research of the author and of others relating to these issues is discussed.     

Neuropsychological profile of adult dyslexics

One hundred and fifteen adults with well-documented childhood reading status underwent a series of neuropsychological tests including tests of memory, attention, phonological processing, and visual perceptual skills in an attempt to define the neuropsychological profile of dyslexia in adulthood. Compared to a normal nonreading disabled sample, subjects with a history of reading disability performed consistently poorer on most neuropsychological tests. However, after covarying for intelligence and socioeconomic status, only tests of rapid naming, phonological awareness, and nonword reading were significant discriminating measures. The hypothesis that deficits in phonological processing comprise the core cognitive deficits in adults with a history of reading disability was supported. Independent of current adult reading ability, measures of nonword reading, phonological awareness, and rapid naming serve as indicators of a childhood history of reading disability.     

Multivariate Familial Analysis of Cognitive Measures in the Colorado Family Reading Study

Multivariate path analysis is employed to examine the etiologies of variation and covariation of three composite cognitive measures in the Colorado Family Reading Study: reading ability, symbol-processing speed, and spatial/reasoning. Measures of phenotypic assortative and cross-assortative mating are incorporated in a multivariate analysis of familial resemblance within nuclear families. Phenotypic variances and covariances are partitioned into components due to familial (genetic and/or family environmental) influences and to specific, nontransmissible environmental influences in families with a reading-disabled child as well as families with children of normal reading ability. Comparable moderate familial influences are found across family type for all three composites and the phenotypic correlations between traits are largely due to familial influences.